Exploring the wonders of geology in response to young-Earth claims...

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Monday, June 30, 2014

What Georgia Purdom could learn from TED Talks

In her recent blog post, Dr. Georgia Purdom of Answers in Genesis criticized an article by Dr. Scott Kaufman from The Raw Story, who highlighted two projects at a White House science fair to demonstrate some inconsistency on the part of Ken Ham. The Raw Story piece followed up on a claim by Ham that none of the celebrated science fair projects depended on 'molecules-to-man' evolution. Ken Ham apparently sees this as support for his claims that creationism doesn't stifle real scientific development, contrary to the evidence I raised in my last post. Since two of the science fair projects addressed major developments in cancer research, however, Dr. Kaufman was quick to point out the hypocrisy in Ken Ham's claim. He writes:
"The link [Ken Ham] included to the projects presented at the White House Science Fair... lists two studies of the behavior of cancer cells, both of which depend on theories of cellular development that are themselves predicated on evolutionary theory."
According to Dr. Purdom, modern cancer research need not appeal to the principles of evolutionary theory to function. But to make this claim, she must limit evolutionary theory to a piecemeal, nuanced derivative of the original—a rhetorical tactic not well understood by her audience. A more honest approach would be to admit openly: "Well yes, cancer research does draw on principles of evolutionary theory, but I am still critical of and reject several components of evolutionary theory."

I will rely on those of you with stronger backgrounds in biology to clarify, augment, or correct my own position, but to my knowledge, human cancer research interacts with and depends on evolutionary theory in at least two important ways:
1. The genetic elements of cancerous cells are subject to (and often derive from) mutation, and so a major challenge of cancer research is understanding the evolution of individual diseases and the response by individual species (e.g. Davies et al., 2002Domazet-Lošo et al., 2014).
2. The behavior and treatment of human cancers can be assessed through other mammals, like mice (e.g. O'Brien et al., 2007), on the grounds that humans share a common ancestry with these animals.
Like many Americans (perhaps including some of you), Georgia Purdom rejects that humans share a common ancestry with other animals, and she is free to try and defend that position. Chances are, she and likeminded creationists could contribute to ongoing cancer research. But it is fairly misleading to characterize this research as employing only the "tools of good observational science"—presumably in contrast with broken tools of bad, historical science?—or to pretend that evolutionary theory "has nothing to do with it". In the words of Dr. Paul Davies (quoted here), "we will fully understand cancer only in the context of biological history."

Dr. Purdom's mischaracterization of science, which propagates the false dichotomy between 'observational' and 'historical' science, along with her downplaying the role of certain fields in biology, all contribute to the growing negative attitude among evangelicals toward careers in science. The satire piece by Scott Kaufman (who, Dr. Purdom kindly reminds us, only has a Ph.D. in Literature) is thus in line with the thesis of my previous post and elucidates the rhetorical effort by Answers in Genesis to disassociate mainstream geology and evolutionary theory from the rest of science (you know, the part that's 'successful'). So I would like to thank Dr. Kaufman, who—despite his 'meager' credentials—seems to understand the nature of science better than Dr. Purdom and is willing to share that knowledge with others.

"Why we should trust scientists"

The link above is to a recent TED talk given by Naomi Oreskes, a historian of science. Therein, she addresses the paradox of science communication: all of us must appeal to authority—an informal logical fallacy—to accept conclusions reached by scientists outside of our own specialty, but we should still trust scientists and the conclusions they reach in consensus.

Most relevant to this discussion, Dr. Oreskes takes a closer look at the scientific method, which is commonly oversimplified by textbooks. She demonstrates how aspects of observation, hypothesis, laws of nature, and historical evidence have worked in conjunction through a not-so-well defined method. Scientists have to be creative to solve the diversity of research problems they face, and most endeavors will involve both 'historical' and 'observational' methodologies. According to Dr. Oreskes, however, the robustness of the scientific method is not the basis for our trust in scientific consensus. The way she arrives at this conclusion is fairly intriguing, so I won't spoil it here.

In the introduction, this talk appeals to a slight mischaracterization of Pascal's wager and what initially appears to be an unfair contrast of faith and science (keep watching, it's not). In the end, though, I would highly recommend the video to inform your own thoughts on the nature of science and/or facilitate discussion (I suppose that is the goal of TED talks, right?).

Wednesday, June 25, 2014

The U.S. needs more scientists, and Ken Ham isn't helping

In February of this year, millions of Americans tuned in to see how popular scientist Bill Nye would fare in public exchange with Ken Ham, president of the largest organization promoting young-Earth creationism. I've already given my thoughts on the debate, but a few weeks after the fact, a good friend of mine challenged a key accusation from Bill Nye, which got me thinking. During his closing remarks, Nye exhorted the audience to extinguish YEC from the public sphere for the sake of our society:

"I say to the grownups, if you want to deny evolution and live in your world, in your world that's completely inconsistent with everything we observe in the universe, that's fine, but don't make your kids do it because we need them. We need scientifically literate voters and taxpayers for the future. We need people that can — we need engineers that can build stuff, solve problems."

I don't doubt the sincerity of Nye's invitation, with which I (and many of you) can empathize fully. The underlying implication, however, is that one cannot succeed in the natural sciences if one is caught up in the young-Earth paradigm touted by Ken Ham. Being the sharp public speaker that he is, Mr. Ham anticipated this sort of accusation in his opening presentation, during which he broadcasted short interviews with U.S. scientists that accept the young-Earth position. I would conjecture that Nye's exhortation thus fell on deaf ears among the audience, who had just witnessed firsthand that YEC's can be effective scientists and engineers.

Evolution and technological development

In particular, Ken Ham highlighted the work of creationist Raymond Damadian, who invented the MRI. Through this case in point, Ken Ham established well that believing in a young Earth and rejecting evolution does not necessarily cripple you from solving scientific problems and developing the technology needed in our modern world.

Ham proceeded to challenge Nye to cite one piece of technology that could not have been developed apart from accepting an 'old Earth' and 'molecules-to-man' evolution. We should give Mr. Ham credit for making his point clearly, but in the spirit of honest discourse, we must recognize that his challenge is extremely misguided.

In limiting this challenge to 'pieces of technology', Ken Ham subtly tried to link the theory of evolution to all other disciplines, as though this foundational principle of biology were some sort of epistemological framework on which all secular knowledge is built. This overstated connection—completely foreign to actual scientists and most Christians—is illustrated well in a couple graphics used by AiG and creationists around the web. The first appeared in Ken Ham's presentation, as I recall:

According to this cartoon, believing in evolution and/or 'millions of years' constitutes a philosophical framework that sprouts all the world's problems, as well as an attack on the integrity of sacred scripture. Alternatively, this set of beliefs is a tree of 'bad fruit' that is rooted in sin:

What is missing from this implied philosophical connection is a sound argument to support it. The theory of evolution is not morally prescriptive (i.e. it cannot tell you what you ought to do in life); rather, it is an explanatory framework through which relevant data in biology, geology, anthropology, etc. are scientifically coherent. If we share a common ancestry with other primates, it does not logically follow that you can freely rape women (as YEC Darek Isaacs put it). Following the logic of Ken Ham, the observed fact that genocidal dictators with military support often do get their way would imply that they ought to get their way. As for the rest of us, we can distinguish between an objectively descriptive theory in science and a morally prescriptive philosophy.

Ham's false dichotomy between a system where "man decides truth" and "God's word is truth" serves well to keep his audience skeptical of both evolution and mainstream geology. Ultimately, however, we must deal with the fact that to read and understand God's word, we utilize the same cognitive abilities that allow us to reconstruct the common ancestry of life on Earth over millions of years.

Coming back to Ken Ham's challenge, we might be hard pressed to find a piece of technology that demands a belief in evolution or an old Earth. Of course, this is as meaningful as finding a successful businessman who rejects string theory. On the other hand, thousands of scientific instruments (including mass spectrometers, seismic detectors, and equipment to read the human genome) were developed to test hypotheses that confirmed 'molecules-to-man' evolution and an old Earth. Genuine scientific inquiry inspires and facilitates technological development like a catalyst, so as far as I'm concerned, Ham's challenge has been answered countless times.

Why are Evangelicals underrepresented in the sciences?

So it's possible to be a creationist that designs medical equipment, invents better cell phones, or builds spacecraft. But how does the prevalence of young-Earth creationism affect public attitudes toward science? I would hypothesize that by selectively undermining entire subdisciplines (like geochronology, climatology, or evolutionary ecology), Ken Ham and his organization have all but extinguished the genuine curiosity that would otherwise drive members of his audience toward those fields. Why spend 6 years in poverty (i.e. graduate school) to specialize in a subject rooted in lies and bad science? Why contribute to scientific research that begins with a rejection of God's word? Intentionally or not, Ken Ham has scared young scientists from taking the necessary steps to realize their dreams and make an impact on the scientific community. If you believe that the Bible is God's word, and God's word is truth, then this is a step backward for Christianity.

And even if you don't, but still believe that science is foundational to modern society, you can agree this is a step backward for humanity.

Only two weeks after the Ham/Nye debate, Christianity Today reported on a study that confirmed my suspicions. Despite the overall positive tone, given that a large percentage of 'rank and file' scientists identify as Christian, I noticed immediately that Christians are underrepresented in the scientific community compared to the general population. This feature is quantified in Table 5 of the original study by Ecklund (2014) from Rice University:

According to these polling data (n = 10,241), Evangelical Protestants are the single most underrepresented religious group among U.S. scientists. Mainline Protestants and Catholics, who are more likely to accept mainstream biology/geology, are slightly better represented, consistent with my purported connection to the 'science skepticism' of creationist claims. Ecklund (2014, p. 13–14) writes:
"Evangelical Protestants... are more than twice as likely as the overall sample to say they would turn to a religious text, a religious leader, or people at their congregation if they had a question about science."
It is important to note that being religious does not necessarily deter one from becoming a scientist in the U.S. While atheists/agnostics are better represented among scientists, unsurprisingly, it is not nearly to the same extent as Jewish Americans or the catch-all category of Middle and Far Eastern faiths. So I would encourage you to read the original study, which I don't intend to review exhaustively here.


Among religious groups where YEC ministries have the greatest impact, relatively fewer congregants pursue careers in the natural sciences. Ken Ham may believe that one can be an effective scientist as a creationist, and he may be right. But Bill Nye's exhortation to extinguish YEC from the public sphere for the sake of modern society is equally valid. It appears the prevalence of YEC in the U.S. can impact our reputation as a leader of research, technology, and design.

Tuesday, June 24, 2014

"Best evidences for a young Earth": Snelling and our salty seas, Part 3

(continued from Part 2)

In case you are now exhausted by the topic of salt in the oceans, I want to reassure you: this is the light at the end of the tunnel.

Thus far, I have tried to examine closely and honestly the methodology of Austin and Humphreys (1990), which I described as unscientific and oversimplified. By no means is this a personal attack, as I have documented precisely how Austin and Humphreys have ignored or miscited key data and thus employed unjustifiably simple models to convince readers that the oceans must be younger than 62 million years. They tout confidence not shared by the very authors they cite. Furthermore, they have been resilient in the face of criticism, refusing to update their model despite that more research is available every year, which could drastically improve it.

In the last post, I focused on the various mechanisms by which sodium is added to the world's oceans. By reading through all sources cited by Austin and Humphreys, as well as newer studies from the past 24 years, I found numerous flaws in the 'sodium inputs' reported by Austin and Humphreys and utilized in their model. Most of their figures far overestimated the amount of sodium carried to the oceans, and some of the proposed mechanisms add no sodium whatsoever on geological timescales. These authors are thus guilty of some basic errors in accounting, as well as some basic misunderstandings of geochemistry, for which they ought to be held responsible. But that is the nature of science: we open our research to criticism, by which it might be refined. If we refuse to accept that criticism, science cannot advance.

In this final post, I will briefly address the 'sodium outputs' reported by Austin and Humphreys (1990), followed by a 'balanced checkbook' of the global sodium cycle that shows why the oceans are not missing salt.

Table 2 from Austin and Humphreys (1990), summarizing
model outputs of Na from the ocean. Units are in 1010 kg/yr.
Sodium Outputs

1. Sea spray

One of the most active and constant processes by which salt is removed from the oceans is felt by anyone that spends much time at (or lives near) the beach. Rust and corrosion are constant worries for any machinery exposed to the sea breeze, which is full of salty droplets of water. Austin and Humphreys (1990, p. 5) describe sea spray rather well:
"Waves of the sea, especially breaking waves along the shore, produce air bubbles in the water. Collapse of these bubbles shoots into the air droplets of seawater which evaporate to form microscopic crystals of halite. Crystals of halite are carried with other aerosols by the winds from the ocean to the continents."
While sea spray does remove massive quantities of salt from the oceans (Austin and Humpreys estimate 60 million tons/year of sodium, Table 2), the vast majority of this salt returns swiftly to the oceans via rivers and groundwater. You may recall from last post, I likened the process to withdrawing $20 and immediately re-depositing the money into your account. Since I determined the long-term sodium input from sea spray to be 0 tons/year, we must also remove sea spray as a sodium output.

By comparing Table 2 to Table 1 from Austin and Humphreys, we find that sodium lost via sea spray is greater than sodium gained by ~5 million tons/year. I cannot say whether this imbalance was intentional, but it may reflect a real, albeit minor, long-term loss of sodium to the continents. For example, some sea spray particles will end up falling as rain over the Great Basin of the United States, but no rivers drain from the Great Basin to the oceans. In other words, these bits of salt will eventually get buried in sediments or groundwater storage on the continent, providing a long-term sodium sink.

From a 'deep-time' perspective of geology, those continental reservoirs of sediment and groundwater may eventually be uplifted and eroded into the oceans. Therefore, it becomes impractical to calculate precisely how much sodium is lost, long-term, via sea spray; we simply know that the amount should be greater than zero.

For the purpose of this discussion, I will follow Holland (2005) and consider the long-term sodium output via sea spray to be 0 tons/year. But we might allow the sodium loss to continents to be as high as the minimum imbalance from Austin and Humphreys (1990), which is 5 million tons/year.

2. Ion exchange

Cation exchange is a blessing to those with 'hard water', as water softeners work by exchanging calcium and magnesium for 'softer' ions like sodium. In the oceans, the process works in reverse: clay minerals tend to absorb sodium while releasing calcium and magnesium back into the oceans. Since clay minerals are abundant as suspended particles in river water, the rivers deliver millions of 'sodium-absorbent' sponges every year.

Austin and Humphreys cite a handful of studies that attempt to estimate the total uptake of sodium via cation exchange. These estimates have not change substantially in recent years, and Holland (2005) uses the same figure (35 million tons/year) in his table. Of course, the total amount depends strongly on the amount and composition of sediments delivered to the oceans, which means that it will vary on geological timescales with riverine inputs of sodium. Therefore, we can take the flux used by Austin and Humphreys as a reasonable, if not a high-end, estimate of sodium lost via cation exchange: 35 million tons/year.

3. Burial of pore water

Marine sediments dominated by clays in particular are extremely porous, meaning that abundant seawater is present between the particles. In short, the seawater gets buried within the sediments, along with the salt it contains. Austin and Humphreys cite an earlier, rather crude estimate of sodium loss via pore-water burial of 22 million tons/year.

We should note that pore-water burial is a complex process, accompanied by numerous chemical reactions (e.g. Scholz et al., 2013). Therefore, it is difficult to estimate precisely the total flux of any element, let alone sodium. In addition, the rate at which marine sediments are buried will vary on geological timescales, depending on the rate and character of global tectonics. During the formation of major mountain belts (like the Andes, Rockies, and Sierra Nevadas), we should expect greater rates of sediment accumulation and pore-water burial, in particular because such mountain ranges are accompanied by deep-water ocean trenches, in which miles of sediment accumulate relatively 'rapidly'.

4. Halite deposition

Austin and Humphreys' assessment of halite (NaCl) deposition is rather misleading. They note correctly that modern marine sediments are "nearly devoid of halite", but do not address completely why this would be characteristic of Earth history. Halite deposition is limited by the fact that halite (NaCl, or 'table salt') is extremely soluble in water. For seawater to precipitate NaCal typically requires that a body of seawater become isolated from the oceans, after which an evaporative basin forms under intensely arid conditions. One example of this phenomenon in relatively recent geological history is the Mediterranean Sea, under which thick deposits of salt are buried under younger sedimentary layers. The Natural Historian blog on this topic provides an excellent graphic description of the process and these Mediterranean deposits.

In their discussion, Austin and Humphreys (1990) do acknowledge the existence of such halite deposits in the geologic column, but do not consider it to be a significant sodium sink. To establish this, they divide the global inventory of Phanerozoic halite deposits (4.4x1018 kg of sodium) by the length of the Phanerozoic (they use 600 million years) to produce a 'time-averaged estimate' of sodium loss through halite deposition: 7.3 million tons/year of sodium. This number is much smaller than other fluxes of sodium to/from the oceans, so they proceed with confidence (p. 8):
"...it is extremely unlikely that the “time averaged” halite output contains a significant error. No major quantity of halite in the earth’s crust could have escaped our detection."
Austin and Humphreys derive their estimate of global halite deposits from an earlier study by Holland (1984). Now, what might have changed since 1984? For one, the ability of salt deposits to prime crude oil for harvest has made them a valuable target for petroleum exploration in recent decades. Hence we know far more now about the extent of halite deposits than we did 30 years ago.

As it turns out, the global inventory of halite deposits (~32x1018 kg; Hay et al. 2006) is ~3 times larger than the estimate used by Austin and Humphreys. Based on fluid inclusion analysis and mass balance calculations, Hay et al. (2006) further estimate that about 50% of halite has eroded back into the oceans over the course of the Phanerozoic (an assumption shared by Austin and Humphreys). According to these data, the time-averaged flux of sodium from the oceans via halite deposition is ~35–41 million tons/year. This figure is close to the maximum flux via halite deposition in Table 2.

Figure 5 from Hay et al. (2006); the distribution of halite deposition by
geological age over the course of the Phanerozoic. Large outcrops of
Cretaceous (K) aged salt deposits are known from Texas, Mexico,
Portugal, and Spain.
In the last post, I suggested that sodium inputs/outputs via chloride solution and halite deposition should not be included in a long-term model of the sodium cycle, because eventually, these halite deposits will be eroded back into the oceans. Technically, we could remove both quantities from the final table. Having included them, however, we can confirm that the estimated fluxes I've provided are consistent with observed data. If, on average, 38 million tons/year of sodium are removed from the oceans via halite deposition, and 17.6 million tons/year of sodium are added to the oceans via chloride solution in rivers, then we can expect that after 600 million years, 12.2x1018 kg of sodium should now be locked up in Phanerozoic halite deposits. Since sodium is 1/3 the mass of halite (NaCl), that makes 36.6x1018 kg of halite. This figure is only slightly more than 32x1018 kg, the documented global inventory of Phanerozoic halite deposits from Hay et al. (2006). Within uncertainty, therefore, my refinement of Austin and Humphreys' model is accurate for the past 600 million years.

5. Alteration of basalt

Sodium removal via low-temperature alteration of basalt on the seafloor constitutes a relatively minor sink. This rate is dependent on that of seafloor spreading, and so it will vary over geological history, but the total flux is too small to impact significantly the final calculation. I don't see anything problematic with the figure, so I will keep Austin and Humphreys' cited flux of 4.4–6.2 million tons/year of sodium.

6. Albite formation

I discussed at length in the last post why albite formation is a significant sink of sodium from the oceans and concluded that 25.3 million tons/year of sodium are removed via this process. This is one of the more significant errors in the model by Austin and Humphreys (1990), who mistakenly supposed that sodium was added to seawater through off-axial vents near mid-ocean ridges.

7. Zeolite formation

This final sodium output is likewise so small, that it will scarcely impact the final calculation. Again, I see nothing problematic with the figure cited by Austin and Snelling, so I will leave it intact.

The Global Sodium Cycle in Perspective

After examining all of the supposed inputs and outputs of sodium to and from the world's oceans, we can evaluate the argument by Austin and Snelling (1990) through an updated table:

Revised table of sodium fluxes to/from the oceans, as compared to Austin and Humphreys (1990). Uncertainty estimates represent 20% of total flux, as suggested by Holland (2005). Therefore, the total sodium input of 138.7 million tons/year is within uncertainty of the total sodium output of 126.4 million tons/year. According to these figures, the oceans are in steady state with respect to the sodium cycle, and the 'salt chronometer' provides no challenge to their conventional age of 3 billion years.
Immediately evident from this revised table is the fact that Austin and Humphreys (1990) significantly inflated and overestimated sodium inputs to the oceans. They accomplished this goal by the selective sampling of literature (some of which was already outdated by the time of their publication) and the use of high-end estimates without reporting uncertainties. In addition, they assumed (sometimes blindly) that these fluxes should stay the same over geological time. In fact, none of them should remain constant over tens of millions of years, given the dynamic complexities of our Earth systems.

The flux of sodium to and from the oceans via these various processes is not extremely well understood, even in the modern day. The processes are complex and must be estimated from limited data. Unfortunately, Austin and Humphreys could not afford to be honest about the nature of geology when it comes to documenting global geochemical cycles. In any case, we may finally put to rest the argument that the ocean's salt content limits the theoretical age to only 62 million years. Given that sodium inputs and outputs are essentially in balance, this upper limit crumbles entirely and is rendered scientifically meaningless.

Monday, June 23, 2014

"Best evidences for a young Earth": Snelling and our salty seas, Part 2

(continued from Part 1)

I have already concluded that attempts by Snelling, Austin, and Humphreys to estimate a maximum age of Earth's oceans are both unscientific and inaccurate. More recent work (e.g. by Holland, 2005) determined that no long-term surplus of salt (or even just sodium) exists that would limit the theoretical age of the oceans to a few tens of millions of years. Regardless, YEC's continue to tout the 'salt chronometer' as convincing evidence against the conventional age of the Earth by citing Austin and Humphreys (1990), whose model has not been updated in more than two decades. Therefore, I want examine more closely this classic YEC model to determine whether it ever offered a valid, scientific challenge.

"The Sea's Missing Salt": Austin and Humphreys (1990) propose a dilemma
"The known and conjectured processes which deliver and remove dissolved sodium (Na+) to and from the ocean are inventoried. Only 27% of the present Na+ delivered to the ocean can be accounted for by known removal processes. This indicates that the Na+ concentration of the ocean is not today in “steady state” as supposed by evolutionists, but is increasing with time. The present rate of increase (about 3 × 1011 kg/yr) cannot be accommodated into evolutionary models assuming cyclic or episodic removal of input Na+ and a 3-billion-year-old ocean. The enormous imbalance shows that the sea should contain much more salt than it does today if the evolutionary model were true. A differential equation containing minimum input rates and maximum output rates allows a maximum age of the ocean of 62 million years to be calculated. The data can be accommodated well into a creationist model." -Excerpt from the abstract, Austin and Humphreys (1990)
The methodology by Austin and Humphreys is as straightforward as balancing your own bank account: subtract your total number of monthly expenses from your total monthly incomes, and you can calculate the net monthly change to the account. Their conclusion is likewise as simple as the following logic: last month, I added $100 to my account, so I currently have $1,100 in the account; therefore, my account could not have been opened more than 11 months ago.

Imagine this describes your bank account, which you actually opened some 20 years ago. You might be quick to respond in several ways: 1) the net change to my account is not always positive, because sometimes I spend more than I earn; 2) the net change to my account has not been $100 every month, but has been more or less in the past; or 3) if there is an error in accounting, I didn't actually add $100 to my account. As it turns out, all three responses can be given to Austin and Humphreys, who—despite more than 30 years of new research on the Earth's oceans and geochemistry—have not updated their 'accounting'.

Table 1 from Austin and Humphreys (1990), summarizing
model inputs of Na to the oceans. Units are in 1010kg/yr.

Sodium inputs
1. Rivers: Sea-spray component
The first item in Table 1 of Austin and Humphreys (1990) indicates that 50–55 million tons of sodium are added to the oceans via droplets of water containing sea salt, which fell into rivers draining into ocean basins. The origin of this sodium, however, is the ocean itself. As waves crash over the ocean, tiny droplets of salty water are carried off by the wind and deposited over the continents. Since this mass of sodium moves directly from the oceans to the rivers and then back again, it should not be included in the table of inputs. If you draw $20 from your account, only to deposit it back into the account, the net change is zero. Therefore, the real influx of sodium via sea-spray input to rivers is 0 tons/year.

2. Rivers: silicate weathering
Austin and Humphreys cite Meybeck (1987), who estimated that ~62 million tons of sodium are dissolved through chemical weathering of silicate minerals (e.g. feldspar) and delivered to the oceans via rivers. This estimate is based on modern analyses of rivers and major watersheds, however, and Meybeck notes that precise masses are very difficult to assess, due to a lack of direct measurements. Assuming the accuracy of their figure, in any case, we should also note how this number (62 million tons) can vary through time. Nobody expects that it would remain constant over hundreds of millions of years.

First, sodium delivery via silicate weathering depends on the global weathering rate, which itself depends on climate, sea level, and global tectonics. Glacial conditions enhance silicate weathering by crushing millions of tons of silicate minerals into fine powder, which gets washed downstream to the oceans. Therefore, sodium delivery should be less for a majority of Earth history, during which glaciers were absent. Higher sea level limits the amount of land (particularly sodium-rich coastal sediments) exposed to chemical weathering and erosion. Therefore, sodium delivery should be less for a majority of Earth history, during which sea level was higher and less land area was exposed. Finally, the formation of large mountain ranges, particularly where annual precipitation is high, contributes substantially to modern silicate weathering. Relatively recent mountain belts like the Himalayan and Sierra Nevadan ranges expose more silicate minerals to chemical weathering and erosion. They also promote strong precipitation (rain/snow) over the continents, by forcing air masses upward. Therefore, sodium delivery should be less for periods of Earth history when massive orogenic belts did not exist.

In any case, more recent work by Holland (2005) provides a better estimate of sodium from silicate weathering. Therefore, the total influx of sodium via silicate weathering should be ≤55 million tons/year.

3. Rivers: chloride solution
In the modern geological setting, a small percentage of the land area (<2%) is comprised of some very salty rocks. These small outcrops of halite, gypsum, and ancient marine clays contribute a relatively huge proportion of sodium to rivers draining into the oceans (today, as much as 75 million tons/year, including agricultural runoff). Quite simply, rock salt is far more soluble than minerals like feldspar, so any exposures of rock salt at the Earth's surface will erode thousands of times faster than, say, granite and other silicate rocks.

Before we consider "chloride solution" to be a long-term Na input to the oceans, however, we need to ask: what is the source of sodium in these rocks? Geologists agree unanimously that these Na-rich minerals were precipitated largely from seawater, either as ocean basins became isolated (e.g. the Mediterranean Sea) when sea level was much lower, or as warmer climates evaporated more water from shallow seas. Whatever the mechanism, this source of sodium to the oceans ultimately derived from the same oceans! That being the case, Austin and Humphreys are wrong to include this flux in their table without adding it directly to the other side, because in the long-term, no more sodium can be dissolved from marine salt deposits than was removed at some point in the past.

In terms of our analogy from accounting, imagine that you sporadically withdrew money from your account and hid $20 bills around your house. Whenever these bills resurfaced (say, during 'Spring Cleaning'), however, you took the money back to the bank and re-deposited it into the same account. The amount of money going back into your account cannot be more than the amount originally withdrawn (wouldn't that be nice!). But according to the accounting by Austin and Humphreys (1990), an average of 75 million tons of sodium were added to the oceans every year, despite that less than 40 thousand tons (see Table 2) were 'withdrawn', on average, each year. Austin and Humphreys have failed miserably in this simple test of accounting.

So we have determined that Na from "chloride solution" should not be included in the table of Na inputs, so the actual number should be 0 million tons/year. I will include it here, because I will also consider Na removed by halite deposition, as Austin and Humphreys have done. However, I use a more reasonable estimate of long-term "chloride solution" using the data of Hay et al. (2006), who estimated halite burial and erosion over the course of the entire Phanerozoic. These data take into account the fact that at various points in Earth history, more or less halite has been exposed at the Earth's surface. As it turns out, the total area of 'salty' outcrops (~1.3%) is much higher today than for the bulk of Earth history, because most of these outcrops are only Miocene in age. Prior to the Miocene, (>23 million years ago), these salt deposits didn't exist and therefore could not have been dissolving back into the oceans. The amount of salt being dissolved from evaporite minerals and added back to the ocean has fluctuated substantially over time:
Estimated influx of Cl- to the oceans over the Phanerozoic, according to
Hay et al. (2006). Each atom of Cl- should be accompanied by one Na+.
The average influx of sodium via "chloride solution", according to data from Hay et al. (2006), was about 17.0–18.3 million tons/year, much less than the figure cited by Austin and Humphreys.

4. Ocean floor sediments

As marine sediments accumulate on the ocean floor, the uppermost centimeters of sediment tend to release sodium into the ocean while absorbing both Mg and Ca. This phenomenon was quantified for Atlantic Ocean sediments by Sayles (1979), cited by Austin and Humphreys. A later review of the topic by Drever, Li, and Maynard (1988) also cited Sayles (1979), whose estimate appears in Table 1.4 of their paper. This is the figure used by Austin and Humphreys (1990), who conclude that 5.0 x 1012 moles/yr of sodium (1.15 x 1011 kg/yr) are added to the oceans every year by this process. It is the largest single input of sodium used in the model by Austin and Humphreys (Table 1).

Although nobody questions that the diagenesis of ocean sediments (i.e. their chemical modification after burial) releases Na into the oceans, the calculated magnitude is very much in question. Drever, Li, and Maynard (1988) also include a previous estimate by Maynard (1976), which is 6 times smaller than the figure by Sayles (1979). Even the more comprehensive data from Sayles (1979) indicate substantial variation in this flux from one location to the next, and by no means have all the world's oceans been studied in this manner. Drever, Li, and Maynard (1988) conclude:
"...it seems likely that the relative changes in [Na+] are correct but the absolute magnitudes are too high by a factor of at least 2." (emphasis mine)
If we take the advice of Drever, Li, and Maynard (1988), whom Austin and Humphreys (1990) cite to obtain their figure, then the actual flux of sodium from ocean-floor sediments should be ~52.5 million tons/year or less. The associated error bars are high, however, and we can expect this flux to have varied over Earth history, since it depends strongly on the amount and composition of sediments delivered to the oceans.

5. Glacial silicates

Austin and Humphreys include the sodium input from "finely pulverized glacial silicates", which they estimate crudely from the volume of rock being eroded by the Antarctic Ice Sheet. This process is important today, because most of Antarctica is covered by active glaciers. These massive ice sheets are missing, however, from the majority of Earth history. In fact, tropical plant fossils are common among sedimentary layers from Antarctica. Therefore, the estimated 39 million tons/year of sodium from "glacial silicates" is not applicable to a long-term model of the sodium cycle.

In addition, there is no direct evidence for how much sodium is shed from the Antarctic continent and dissolved in seawater, and the estimate by Austin and Humphreys is certainly way too high. The only study they cite is from 1964 and did not address sodium dissolution directly, let alone in Antarctic waters. Nonetheless, they assume that 64% of all glacially eroded rocks dissolve completely in seawater rather than accumulate as sediments. Is this realistic? Not at all.

The actual long-term influx of sodium from glacially pulverized silicates is slightly more than 0 million tons/year, but far less than the 39 million tons estimated by Austin and Humphreys. Even if we use their figure, we should multiply it by the small fraction of Earth history during which large continental glaciers existed, which yields ~1 million tons/year.

6. Atmospheric and Volcanic Dust, and 7. Marine Coastal Erosion

Austin and Humphreys once more make gratuitous assumptions about how much silicate dust/sediment completely dissolves in seawater. Their estimates of Na influx from these two processes are so low, however, that ignoring them completely would not change the total estimate of sodium inputs. Therefore, I will include their estimates to be generous/conservative.

8. Glacier ice

Yet again, Austin and Humphreys include a relatively insignificant process that is not applicable to the majority of Earth history. They estimate that ~1.2 million tons/year of sodium are added from glacial ice containing salt trapped from the atmosphere. If the glaciers were absent, however, this tiny amount of halite dust would either be washed back to the oceans through rivers or buried in surface sediments. Once again, I will include their estimates to be generous/conservative, but I want to highlight the unscientific nature of their methods, which they employ under the guise of being thorough. If we have no reason to expect that large glaciers were present for the past 62 million years, then why include this flux in a model that supposedly characterizes the last 62 million years of Earth history? Austin and Humphreys most certainly know better, so the fact that glacial ice is included as a sodium input reveals the dishonest tactics behind their work.

9. Volcanic Aerosols

This flux depends, of course, on rates of volcanic activity, which undoubtedly varied in Earth history. Nonetheless, this sodium input is far less than the uncertainties of other large fluxes, so it matters little whether the flux is included in the total calculation.

10. Groundwater seepage

According to Austin and Humphreys, large amounts of groundwater are seeping into the oceans, carrying some 96 million tons/year of sodium with them. This is the second largest input of sodium from Table 1—how is it calculated? Citing Garrels and Mackenzie (1971), they take the difference between global runoff and global rainfall minus evaporation to be the amount of groundwater seeping from continent to oceans every year. They then multiply this mass of water by what they assume to be the average sodium concentration of groundwater.

This almost makes sense, intuitively. Imagine you poor 100 liters of water into a large wooden planter, of which 10 liters evaporate into the open air. Now, 90 liters of water remain somewhere in the planter. Imagine now that 80 liters leaked out of the planter onto the lawn through cracks between the wood (much like rivers discharging into the oceans). What about the remaining 10 liters of water? We must assume that this mass of water infiltrated through the planter and seeped into the ground on which the planter is situated, right?

Not entirely. We can be certain that some of this water will be stored in the planter itself. Likewise, some 3.3x1020 kg of water on Earth is now stored on the continents in underground reservoirs, because not all precipitation ends up in the oceans. Therefore, Garrels and Mackenzie (1971) take the difference (used by Austin and Humphreys) as a maximum estimate of groundwater flow to the oceans. Given the large errors in calculating global precipitation, evapotranspiration, and runoff, they further write:
"Conceivably this excess could be delivered by subsurface flow. If so, and if these ground waters have about the same total salinity as streams, approximate 4x1014 g/year of dissolved solids could be entering the ocean basins from subterranean flow. Both required assumptions are shaky; from the preceding discussion of stream discharge it is clear that a 10 percent difference between total precipitation minus evaporation and stream discharge could be accounted for by errors in either estimate. Also, we do not have good numbers for the dissolved solid content of those ground waters reaching the sea." (emphasis mine; from this quote, we learn that groundwater may or may not be seeping into the oceans in large quantities)
So Garrels and Mackenzie (1971), writing in an era before satellite constraints on the global hydrological cycle, proceed with caution in estimating the maximum plausible influx of sodium to the oceans from groundwater (which they estimate to be 20 million tons/year, a meager 20% of the value used by Austin and Humphreys). Regardless, Austin and Humphreys use a high-end estimate of groundwater seepage with confidence and further imagine that groundwater seeping into the ocean is, on average, 5 times saltier than river water. They provide no direct evidence of this figure, to which they attach almost no uncertainty (unlike Garrels and Mackenzie, whom they cite). On the contrary, they suggest only that it might be even higher!

Since groundwater seepage to the oceans occurs mainly from shallow, coastal aquifers, it is rather reasonable to assume that groundwater seeping into the oceans is about as fresh as rivers draining into the oceans, and not five times saltier. Very saline groundwater is found only in deep, continental aquifers, or coastal aquifers where recent salt deposits exist (e.g. around the Gulf of Mexico). The strategy of Austin and Humphreys, therefore, is one of selective sampling of ballpark estimates from rather old scientific literature, after which errors/uncertainties are ignored or minimized unrealistically.

Since Garrels and Mackenzie reviewed estimates of global precipitation, evapotranspiration, and runoff in 1971, ongoing research and technological development has provided the scientific community with far more accurate and comprehensive data. A more recent assessment of the global water cycle is presented by Trenberth et al. (2007), from which I took the figure below.

Figure 1 from Trenberth et al. (2007); summary of the modern water cycle.
According to their review of data published within the last decade, the difference between surface runoff (40 thousand cubic km) and precipitation minus evapotranspiration (113 - 73 thousand cubic km) is precisely zero. In other words, groundwater seepage is not a significant flux of water to the oceans, and should occur only locally or in response to minor climate fluctuations.

Before concluding, we should be thorough scientists and ask: what is the source of sodium dissolved in this groundwater seeping into the oceans? We cannot answer precisely, but we can be certain that much of the sodium in groundwater (like in river water) derives from either sea spray or dissolved halite deposits underground. Since the sodium in sea spray or halite deposits derives directly from the oceans, we should remove that amount from any long-term model of the sodium cycle (again, we are simply re-depositing money withdrawn from the same account).

Taking all of these factors into account, we may conclude that the total influx of sodium from groundwater seepage cannot be higher than 20 million tons/year, as estimated by Garrels and Mackenzie (1971, Table 4.11). More likely, however, the total long-term input is effectively 0 tons/year.

11. Seafloor hydrothermal vents

The final sodium input used by Austin and Humphreys (1990) constitutes their most egregious error in accounting. They claim that ~15 million tons/year of sodium are added to the oceans from water cycled through hydrothermal vents on the seafloor. In fact, a wide base of scientific literature from the past 3 decades, including papers cited by Austin and Humphreys, proves just the opposite: hydrothermal vent systems remove sodium from the oceans, and they do so in massive quantities. This major error was first documented by Glenn Morton in an open letter entitled Salt in the sea. Dr. Snelling even acknowledges the error (though subtly) in his summary article:
"Long-agers also argue that huge amounts of sodium are removed during the formation of basalts at mid-ocean ridges, but this ignores the fact that the sodium returns to the ocean as seafloor basalts move away from the ridges." (notice, he makes no attempt to refute the claim that sodium is removed during basalt formation, but only to misdirect the accusation)
Unfortunately, Dr. Snelling offers no evidence for his claim that sodium taken up at mid-ocean ridges eventually returns to the ocean (mainly because he is wrong—it does not). The process by which sodium is removed from oceans through hydrothermal vent systems is called albitization. In short, feldspar minerals in oceanic crust (being created constantly at mid-ocean ridges) are converted from calcium-rich feldspar to sodium-rich feldspar in the presence of hot seawater. This chemical alteration releases calcium into the oceans in exchange for sodium, balancing the global cycle. Bach and Früh-Green (2010) write:
“Alkali elements [e.g. sodium] are leached from the rocks by seawater-derived fluids in high-temperature, axial, hydrothermal processes, while in low-temperature ridge-flank systems, they are transferred from the circulating seawater to the oceanic crust. The net effect is that oceanic crust is a prominent sink for alkali elements...” (emphasis mine)
As oceanic crust moves away from mid-ocean ridges, the crust's temperature drops and hydrothermal vents become less active. The majority of newly formed albite is crafted deep within the oceanic crust, however, and is not exposed to seawater once hydrothermal waters cease to circulate. Bach and Früh-Green (2010) add:
"Hydrous minerals (smectites, zeolites) and carbonates form in these ridge-flank systems and slowly seal the crust, which also becomes increasingly insulated from the ocean by the accumulation of sediments." (emphasis mine)
Snelling's misdirection is thus wildly inaccurate; this major sodium sink does not return to the oceans. Therefore, Austin and Snelling (1990) have listed a sodium input that should be counted as a sodium output. So what is the magnitude of sodium lost to oceanic ridge systems?

The uptake of dissolved sodium by mid-ocean ridge processes was noted by Holland (2005), who follows Berner and Berner (1997) and estimates that it accounts for ~25.3 million tons/year of sodium drawn out of the oceans. I devised my own calculation using chemical data from 152 hydrothermal vents (documented by 5 separate papers, listed below), and multiplied the average sodium loss through hydrothermal vents by the estimated volume of water circulated through those vents. Using this method and taking all uncertainties into account, I estimated that the total sodium loss via albitization is 11–47 million tons/year. This figure encompasses the estimate by Berner and Berner (1997), so I am fairly confident in the results. (Note: contact me if you would like to see my original data/calculations, which are too large to paste here).

The major error of Austin and Humphreys (1990) is one of basic geochemistry. They concluded that hydrothermal vents add sodium to the oceans because water emitted by those vents contains a higher concentration than seawater, but this approach ignores the fact that water itself is lost in the process of hydrothermal alteration. In other words, when newly formed oceanic basalt is exposed to hot seawater, not only does it take up sodium into its mineral structure, but it also absorbs water. Therefore, we cannot use the concentration of sodium (i.e. total grams of sodium per liter of water) as a guide to estimate sodium loss/gain, because we know that water itself is lost in the process. Instead, we must use the ratio of Na/Cl in hydrothermal vent water relative to that of average seawater (chlorine is not lost or gained, so it will stay constant). As Reeves et al., 2011 put it:
“Endmember Na/Cl ratios... are all lower than the seawater ratio, consistent with the removal of Na during albitization...”
Despite this basic error in geochemistry, YEC ministry sites continue to reference the work by Austin and Humphreys unreservedly, propagating the false notion that sodium is constantly added to the oceans through hydrothermal vents. I hope you can sympathize with the challenge that we critics of YEC face: it is far easier to spread misinformation than to correct it.


Thus far, I have only addressed the inputs of sodium estimated by Austin and Humphreys (1990), but we can see already that these authors employ a rather deceptive strategy to win over their young-Earth audience. Most of these fluxes are calculated by ignoring basic geochemistry or selectively citing high end estimates, even when the cited authors advise against it. In the next article, I will briefly examine their estimates of sodium outputs to see if the integrity of their research improves. Concluding there, I will provide a revised table that more accurately reflects the sodium cycle and proves that world's oceans are just as salty as we might expect on a 4.5-billion-year-old Earth.

(to be continued...)

References for hydrothermal vent calculations:

Von Damm (1995)
Von Damm et al. (1998)
Seyfried et al. (2003)
Seyfried et al. (2011)
Reeves et al. (2011)

Monday, June 16, 2014

Earth's 'Underground Ocean': No remnant of the Flood

I suppose every good science story deserves a creative headline. Reporting the latest research on the boundary between the upper and lower mantle, however, were catchy titles like this:

• New evidence for oceans of water deep in the Earth
• Splash! Three times as much water as ALL of Earth's oceans found TRAPPED underground
• Evidence Supports Existence of Oceans of Water in Earth
• Earth's 'underground oceans' could have three times more water than the surface

Anyone that understands young-Earth creationism and how it processes scientific reports should be able to anticipate this optimistic, yet naïve response: "Well that explains where all the water from Noah's flood went. We creationists have been saying all along that the highest peaks were once covered by water!" I've seen it pop up on several occasions, despite that neither AiG nor ICR have yet made this connection [correction: Dr. Liz Mitchell of AiG has; see comments to this post]. In any case, it may have something to do with a statement reported here (last paragraph) by Dr. Stephen Jacobsen, a co-author on the paper:
"We should be grateful for this deep reservoir... If it wasn't there, it would be on the surface of the Earth, and mountain tops would be the only land poking out."
The results from Schmandt et al. (2014) are by no means trivial, and personally I am fascinated by continuous geological discoveries so far removed from direct observation (perhaps it is the geological equivalent of deep space monitoring and theoretical physics). But the creative headlines are a bit misleading as to the nature of these deep-mantle 'reservoirs' of water. As Real Clear Science reports (along with the actual text of those articles cited above), melt zones near the transition between the lower and upper mantle (~600 km below the surface) are being produced by dehydration of a mineral called ringwoodite, which is up to ~2.5% water by weight.

Sample of diamond with a tiny inclusion of ringwoodite—the first direct evidence of a deep mantle reservoir of hydrous olivine. Image from Pearson et al. (2014).

The water is present only as single oxygen and hydrogen atoms (–OH) bonded to the most common mineral in the Earth's mantle: olivine, a ferromagnesian silicate named after its characteristic color. If mantle rocks containing ringwoodite sink below the transition zone, the ringwoodite breaks down into its constituent parts: olivine and water. Despite that the concentration of water is never high enough to make droplets of liquid water, these free molecules diffuse into the lower mantle rocks, lowering their melting point. A similar reaction occurs when we spread salt over ice. Salts break down into cations and anions (like calcium and chloride), which lowers the melting point of the ice and allows it to convert from solid to liquid without raising the temperature.

Partially melted mantle rocks (not entirely liquid, because only a small percentage actually melts) are more buoyant than those surrounding, which forces them to rise toward the surface of the Earth. Within the transition zone, however, any free water molecules would simply react with olivine and convert back to ringwoodite. This metamorphism completes the cyclic process that, according to Schmandt et al. (2014), maintains a transition zone containing ringwoodite over a partially melted boundary between the upper and lower mantle. This boundary is detectable through seismic data, according to the authors.

Is there any connection to the Flood?

It has long been known that hydrous minerals like amphibole, along with marine sediments, cause dehydration melting in the upper mantle, which is a major cause of volcanism associated with subduction zones (e.g. Japan, New Zealand, the Pacific Northwest). This process occurs primarily at much shallower depths than the mantle transition zone, however, which means that relatively little surface water is subducted to depths >525 km, where these 'underground oceans' currently exist. In addition, these reservoirs and mass transfers are all part of the global water cycle. The more water that is subducted below the surface, the more volcanism returns it to the surface. Therefore, the deep reservoirs of water hypothesized by Schmandt et al. (2014) could not possibly be remnants of a surficial flood from any point in Earth history.

Besides, the subduction of lithospheric plates occurs at rates so slow, the 'Flood waters' could not have completed even 1% of their journey since ~4,500 years ago.

How should we understand Dr. Jacobsen's statement?

In saying that "we should be grateful for this deep reservoir", Dr. Jacobsen does not imply a one-way, high-capacity conveyor between water on the Earth's surface and water in the deep mantle, which could have sequestered massive oceans. He means rather that if it were not for the constant conversion of water and olivine to ringwoodite within the transition zone, this water would have been added slowly back into surficial reservoirs through volcanism. Instead, it is locked up in minerals as solid as your own jewelry, so that Earth's water content is split between liquid reservoirs in the surface and mineral reservoirs deep underground.

So, the case against Flood geology remains: there is not sufficient water on the surface of the Earth to have covered all its continents with a worldwide flood. Where did the water come from? And where did it go?

Thursday, June 12, 2014

"Best evidences for a young Earth": Snelling and our salty seas, Part 1

Is our universe is full of clues that it cannot be millions—let alone billions—of years old?

Many young-Earth creationists are convinced this is the case, despite that no scientists are scrambling to counter their claims. To understand why, I want to continue my review of Dr. Andrew Snelling's 10 Best Evidences from Science that Confirm a Young Earth, which attempts to equip readers with a set of foolproof arguments in favor of that position. Most recently, I examined Snelling's claim that given the modern ocean-sediment flux, our oceans cannot be more than 12 million years. It took little effort to expose the misleading tactics of Dr. Snelling, however, who miscited key papers and ignored some basic geological principles and data to build his argument. In the end, we find that the ocean-sediment flux offers no challenge to those who accept the conventional age of the Earth and its oceans.

Dr. Snelling and others have employed similarly deceptive methods to claim that our oceans should be much saltier, if indeed they are ~3 billion years old. According to Evidence #9, Very Little Salt in the Sea, more salt enters the ocean every year than is removed by natural processes. Dividing the total salt content of the oceans by the net rate at which salt accumulates yields a maximum age of 62 million years.

Figure 1 from Snelling (2012), illustrating basic inputs and outputs of Na
to the modern oceans. He cites a maximum age of 42 million years, rather
than 62 million years estimated by Austin and Humphreys (1990), whom
he cites (perhaps a typo?).

History of the 'Salt Chronometer'

Dr. Snelling is following in the footsteps of Edmund Haley (1715) and Irish physicist John Joly (1899), who first proposed quantitative methods by which the maximum age of the Earth could be calculated from the ocean's salt content (Hay et al., 2006). The latter concluded that assuming a constant influx of salt, no more than 100 million years could have transpired since the birth of originally freshwater oceans. Despite the ingenuity of these early calculations, geologists abandoned the salt chronometer in favor of radiometric dating for one vital reason. Geological history far too dynamic to assume constant geochemical fluxes (whether of salt or anything else), so the upper limits by Haley and Joly became scientifically meaningless. In addition, the discovery of relatively pure, sedimentary salt deposits indicated that salt can and has been removed from the oceans in the past, negating the principle claim by Joly that salt accumulation is an irreversible process.

Decades later, David Livingstone (1963) would revisit this question in terms of the sodium cycle. He confirmed that a net influx of sodium to the oceans did exist, following estimates of riverine delivery by Clarke (1924), by which all dissolved sodium could be accounted for in a few hundred million years. Livingstone (1963) recognized, however, that this upper limit is very sensitive to the estimated volumes of metamorphosed versus un-metamorphosed rocks, since the latter contain more sodium. After correcting the ratio, he concluded that the maximum age of the oceans (based on sodium cycling) could be extended to as many as ~2.5 billion years.

Young-Earth researchers Steven Austin and Russell Humphreys apparently were not satisfied with the work by Livingstone, so they devised their own assessment of the sodium cycle and its implications for the maximum age of the oceans. They presented their full-length paper in 1990 at the Second International Conference on Creationism, and it is this work primarily on which Dr. Snelling bases his claim that the modern oceans contain too little sodium for an old Earth.

Sodium, not salt

Sea salt consists of more ions than just sodium (Na+), so it should be noted up front that the titles of these YEC works are a bit misleading. The claim by Snelling, Austin, and Humphreys is not that the oceans are missing 'salt', but rather that if the modern, net flux of sodium (as calculated by Austin and Humphreys, 1990) is extrapolated blindly into the past, we arrive at a zero concentration of sodium about 62 million years ago. As with Snelling's examination of the ocean-sediment flux, this methodology is extremely simplistic and involves more assumptions even than the pioneering efforts by Halley and Joly. Hence, it should be obvious why geologists and geochemists are not scrambling to account for the ocean's missing salt: it's not missing.

So why focus on sodium, rather than other major components of sea salt: chlorine, calcium, magnesium, potassium, sulfate, or carbonate? The truth is, of these major ions cycling through the Earth's oceans and crust, we understand sodium rather poorly. Unlike the other elements, sodium does not have multiple stable isotopes, so it is far more difficult to track how it moves from crust to river to ocean to sediment and back again (stable-isotope ratios reflect how much of that element was added/subtracted via specific processes). Another reason that Austin and Humphreys focused on sodium, if I may conjecture, is that sodium is the only element for which there appears to be a positive annual flux to the oceans. If they had chosen to estimate the minimum age of the oceans using chlorine, calcium, magnesium, sulfur, or carbon, they would have arrived at an age of infinity or beyond.

Why are the oceans salty at all?

Before jumping into the details, we should pose this very simple question to YEC's. In the context of an 'old Earth', it makes sense why the oceans contain various dissolved salts in the concentrations observed today: crustal minerals have been weathered and eroded over millions of years, delivering dissolved ions to the oceans via river systems. But why, in the YEC scenario, do the oceans contain massive quantities of salt in the first place? The only answer that may be given is that God simply created the oceans to be salty, with a chemical composition that only appears to have been reached via long, geological processes.

This ad hoc response is typical for the YEC-style, retrospective fitting of data: "God made the oceans salty because otherwise, we can't explain why they're salty". Of course, I will grant that in a divine, fiat creation of the oceans, salty oceans are a hypothetical possibility. But I want to highlight the arbitrary nature of the explanation, because this characteristic is anticipated neither by scripture nor theology. On the contrary, we might expect freshwater oceans from the image of God separating the 'waters above' (the source of rain/snow) from the 'waters below' (the oceans). Salty oceans are not necessary to maintain the abundance of life therein, but rather an impediment to many organisms sensitive to salinity changes. God may as well have made freshwater oceans with marine organisms suited to living in freshwater—why not? Instead, the undrinkable seawater makes the oceans a terrifying desert to humans, among other creatures.

In conclusion, one may speculate as to the divine reason behind the oceans being salty, but the argument will always proceed in the opposite direction of scientific inquiry. This one example elucidates how the YEC paradigm does not arise from scientists examining the same evidence through an alternative worldview. Conventional geologists form testable hypotheses against the evidence until a unifying theory emerges; YEC geologists shake the box of data until a few pieces seem to fit into their preconceived notion of Earth history. The very methodologies are antithetical, and so the resulting paradigms will never converge.

Unscientific procedures

With regard to both ocean sediments and dissolved sodium, YEC's have utilized overly simplistic models to estimate the maximum age of the oceans. It is vital to understand that their conclusions depend on the accuracy of a scientific model, because all models work on a suite of assumptions in an attempt to describe reality. Now, relying on assumptions does not cripple science. On the contrary, it is both necessary and productive, because identifying model assumptions opens them up to falsification, a key component of science. As the saying goes, 'all models are wrong, but some are useful'. We expect from the beginning that Austin and Humphreys' model will be wrong, but to what extent is it useful?

To determine this, Austin and Humphreys need to demonstrate that the intrinsic assumptions of their model are robust. For example, Austin and Humphreys assume that the mass of sodium delivered to the oceans by rivers remains constant over time (or at least within a narrow range). But is this a valid assumption? To my knowledge, neither author has established why the riverine input of sodium could not have varied more substantially in Earth history, though basic geology tells us that it should. The bottom line is, no serious geologist/geochemist attempts to reconstruct Earth history by extrapolating modern rates blindly into the past, so the methodology of Snelling, Austin, and Humphreys is about ~200 years out of date. In my next post, therefore, I will examine the sodium inputs and outputs utilized by their model in light of modern geological principles and studies. How well do you suppose their numbers hold up?

A lot can happen in 24 years...

Since the original publication by Austin and Snelling (1990), little to no attempt has been made to update this common YEC argument for a young Earth. Nonetheless, real geological research has expanded exponentially on this topic, due to advances in technology for surveying the deep oceans. More data are available to estimate riverine inputs of salt and sediment. Major depositional and tectonic events have been discovered or better described, which should impact reconstructions of paleooceanographic conditions (like salinity, sediment recycling, etc.). One of the weaknesses of the YEC approach is that it too commonly relies on a select few papers while ignoring followup research. For example, this paper by Holland (2006) addressed the topic of seawater composition over the past ~550 million years. Was he scrambling to explain why the oceans are not saltier? On the contrary, he writes:
"The sum of the two loss rates [of sodium] is the same, within the uncertainty of the measurements, as the estimated rate of the river input of Na+." p. 231
In reference to the following table of modern and mid-Cenozoic fluxes:

From Holland (2006); summary of Na inputs and outputs to/from the oceans.
I would anticipate YEC's to respond that this approach is too simple (Austin and Humphreys do include more inputs and outputs), but we'll find out in next post why it is not. In any case, we should note that Snelling, writing in 2012, ignored and dismissed the ongoing research since 1990, such as by Holland (2006). For this reason, authors like Snelling may persuade their own audience of YEC readers, but will never impact the scientific community.

(to be continued...)

Additional Reading (from The Natural Historian Blog):

The Salty Sea and the Age of the Earth, Part I – Confirmation Bias
The Salty Sea Part II:  A Young Earth Salt Chronometer?
The Salty Sea Part III: Are the Oceans Getting Saltier Over Time?

Friday, June 6, 2014

Dry me a river: regional and global drought in a warming climate

The American southwest is known for being hot and dry, and for the millions of residents flocking to desert metropolises like Phoenix and Las Vegas, this relatively stable, snow-free climate is one of its major appeals. For those managing its water resources, fighting wildfires, or growing crops, however, the threat of climate change to America's desert landscapes is a serious concern. It's no secret that global temperatures are on the rise, and snowbird states like Arizona have felt the impact (Fig. 1). For the brave few that enjoy Arizona's sauna-like summers, this may not sound so bad. But higher average temperatures and a warmer global climate has detrimental implications for water resources in the American west. Basic physics and climatology tell us to expect the following long-term hydrological impacts in a warming climate:

1) More heat means more evaporation. With all else constant, that means less water staying in soils and feeding rivers/aquifers.
Figure 1: Trend in mean annual air temperature for AZ.
Image from Climate Central's interactive database.
2) Warmer winters mean less snow at higher elevations. Since snowpack is the major source of runoff to rivers and aquifers, that means less water available to plants and humans alike.
3) Warmer oceans means greater storm energy, which results in more water falling in fewer events. Downpours in the southwest produce rapid runoff, which tends to infiltrate less effectively than steady rain/snow. 
4) Warming climate means an expansion and strengthening of the subtropical high pressure belt, which currently contributes to the semi-arid climate of the American southwest. A similar phenomenon during the Medieval Climate Anomaly contributed to the 'megadroughts' (Fig. 2) partly responsible for sudden collapse of several Native American populations, such as the Anasazi.
5) Finally, a more indirect link: global warming has caused a steady decline in Arctic sea-ice volume and extent since the 1970's. A reduction in Arctic sea-ice extent tends to weaken the polar vortex, which means stronger meridional (north–south) atmospheric circulation during winter. Counterintuitively, melting Arctic sea ice results in more frequent winter chills for much of the continental U.S. (as we saw in recent months), but it also means fewer Pacific storms reaching the American southwest (i.e. drier winters). Apart from the monsoon-driven regions, we can expect a significant reduction in effective moisture for the southwest (including California) from this factor alone.

Confirmation of these most basic predictions is available through multiple proxies of drought, which have been summarized in the recent Assessment of Climate Change in the Southwest United States. The authors conclude that despite relatively stable levels of annual precipitation, rising temperatures and reduced snowpack are characteristic of recent decades, of which the most recent (2001–2010) was one of the driest/hottest in over a century. Since ~1980, these trends became distinguishable from the natural background climate variation, according to Barnett et al. (2008), who attributed ~60% of drought trends to forcing by greenhouse gases. Drought reconstructions by Damberg and AghaKouchak (2013) confirm the trend toward drought in the American southwest, which MacDonald (2010) and Dai et al. (2011) note is consistent with the modeled response to global warming and may only get worse.

Figure 2: Last 1,200 years of drought in the southwest. Figure taken from the
Assessment of Climate Change in the Southwest United States.

While the American southwest is no stranger to extreme drought (Fig. 2), the possibility of returning to the climate of the Medieval Climate Anomaly is all but comforting to those managing its water resources. There will always be wet and dry years, but the increasingly robust forecast is that we can expect fewer wet to combat the dry.

Additional climate filters: PDO and ENSO

Figure 3: PDO index since 1950, from NOAA.
One cannot address the question of climate change in the southwest without considering the most prominent, natural thermostats lying just off the coast. Year-to-year climate of North and South America varies substantially due to oscillations in sea-surface temperature (SST) in the Pacific Ocean. This variability is due to the fact that Pacific SST is not geographically homogenous. In some years, it's colder in the east Pacific than in the west (La Niña), while in others, it's warmer in the east Pacific than in the west (El Niño). The Pacific Decadal Oscillation (PDO; Fig. 3) is described by a temperature gradient in the northern Pacific ocean from the middle of the sea to the California coast. The positive index reflects relatively warm waters off the California coast and a weakened high-pressure cell. Weakening of the high-pressure cell allows more storms to penetrate the continent from the cool waters of the northern Pacific. Notice that the PDO tended to be positive during much of the 80's and 90's (Fig. 3). This positive phase was accompanied by wetter conditions in the American west/southwest, refilling of dammed reservoirs, and rapid, optimistic growth in cities like Las Vegas/Phoenix.

The El Niño/Southern Oscillation (ENSO) is the PDO's slightly more chaotic cousin. Comparing figures 3 and 4, however, you can see that they are positively correlated. In fact, the positive trends in ENSO and PDO from 1950–1998 explain why most regions in the southwest have enjoyed slightly more precipitation during the same interval (McCabe et al., 2010), while the negative trends since 1998 partially explain the current 'megadrought'. When precipitation trends (McCabe et al., 2010) are plotted alongside temperature trends (i.e. a measure of potential evaporation and transpiration), it becomes apparent that recent global warming has exacerbated the drought and that future warming will impede drought recovery in decades to come.

Figure 4: ENSO variability since 1950, from the NOAA ESRL.
Given the high variability of naturally occurring climate oscillations like PDO and ENSO, it's not surprising that non-climatologists like Dr. Jay Wile are skeptical of global warming's impact on recent droughts. In my opinion, Dr. Wile has oversimplified the science of climate change and therefore expects a simple correlation between CO2, temperature, rainfall, and drought. But if global warming does affect drought in the southwestern US, that trend will be superimposed on the ENSO/PDO variability shown by figures 3 and 4, and researchers agree that is indeed the case. Dr. Wile cited McCabe et al. (2010) to suggest that the American southwest has not seen more drought, but that study only addressed trends in annual precipitation. Annual precipitation has changed little for the southwest since 1950, and in many parts has increased slightly, but the type of precipitation falling (snow vs. rain) and the timing of that precipitation has changed systematically in response to global warming (Barnett et al., 2008). When all factors are considered, therefore, a more dismal outlook emerges, so McCabe et al. (2010) themselves do not share Dr. Wile's skepticism of global warming or its impact on drought in the southwest.

Global trends in drought: is the Earth as a whole drying up?

In 2013, the IPCC reiterated their long-held assessment (p. 205–206) that in response to global warming, dry regions tend to get drier and wet regions tend to get wetter (see also Seager et al., 2010Trenberth et al., 2014). There are no shortage of studies exploring the impact of global warming on drought, so I am only addressing a fraction of what might be said. Nonetheless, models (i.e. basic physics and climatology) generally predict that with time, we can expect a larger percentage of land area on Earth to be characterized by drought conditions. This seems counterintuitive, because a warming atmosphere simultaneously results in a more intense hydrological cycle (warmer air holds more moisture, for example). However, most of that extra moisture is confined to the equatorial region, high-latitude continental regions (including the Arctic and Siberia), and certain coastal regions, due to the way moisture is transported around the globe. Most models do not predict this change to be catastrophic or sudden, but suggest rather that it will take decades or even a century for average drought conditions to affect some 5–20% more of global land area (e.g. Dai et al., 2013 is a high-end estimate; see Fig. 5). For some regions, it is predicted that drought will increase from reduced precipitation, whereas in other regions, drought will increase primarily from enhanced evaporation as air temperatures continue to rise, or from enhanced SST, which affects pressure patterns and atmospheric circulation.

Figure 5: Slide 36 from a presentation by Aigou Dai (PDF here), illustrating modeled
drought response to enhanced SST under global warming scenarios.

Has global drought increased over the past century in response to global warming? It may sound like this is an easy prediction to test, but it's not. The key factor lies in how 'drought' should be quantified. One classical formulation, called the Palmer Drought Severity Index (PDSI) calculates the effective water balance by comparing total precipitation to the solar energy available to evaporate that water. Several researchers have criticized the use of PDSI to quantify drought solely because of its simplicity (i.e. it doesn't take into account actual soil moisture, wind velocity, and other factors that affect evaporation). In other words, although PDSI can track drought from a basic climate perspective, it may overestimate actual evaporation and thus real risk of drought to agriculture.

To correct this bias, researchers like Hao and AghaKouchak (2013) have devised a more comprehensive metric for drought to forecast crop shortfalls. This metric was applied to the globe by Hao et al. (2014), who captured historical droughts over the past 30 years. No significant trends emerged from the reconstruction, which may suggest that global drought has not increased with global temperature (of course, neither has it decreased). I would caution against over-interpreting historical trends from their plot, however, since it was not their intent to answer how global drought has responded to global warming trends. In fact, their data cover a very short period of time (1982–2012), during which a shift from a predominantly El Niño to La Niña conditions explains why global drought appears slightly more extensive at the beginning of their record. Furthermore, the driest regions on Earth were omitted from their reconstruction, due to their high sensitivity to changes in precipitation. Finally, given their emphasis on soil moisture in the drought metric, it is likely that extensive crop irrigation and management will artificially mitigate the level of drought severity in some major watersheds. The areal extent of irrigation (which affects semi-arid regions already susceptible to drought) has increased steadily from 1982 to present, and since humans irrigate and rotate crops in response to short-term climate variability, human activity on land can blur long-term trends according to this measurement of drought.

On the other hand, Sheffield et al. (2013) also criticized the simplicity of classic PDSI formulations and argued that global drought has changed little in response to global temperature rise. To accomplish this, Sheffield et al. (2013) devised a better formulation of PDSI, which incorporated more variables to estimate real evaporation, and reconstructed global drought trends for the past 60 years (Fig. 6).

Figure 6: Global drought over the past 60 years, from Sheffield et al. (2013),
using the classic PDSI metric (blue) and a more rigorous calculation (red).
The blue lines in Figure 6 are similar to the reconstruction by Dai (2011), who demonstrated that PDSI has decreased substantially (i.e. more prevalent drought) over the past 50 years on a global scale. This conclusion by Dai (2011) cannot easily be ignored, since is corroborated by evidence of enhanced evapotranspiration (Wang et al., 2010) and reduced streamflow (Dai et al., 2009) during the modern warming period. The latter is a more direct measurement of effective moisture over land, since it relies less on computer models to reconstruct trends (keep in mind, all reconstructions of global drought are modeled interpolations of historical data, and so all have intrinsic uncertainties). One important proxy not considered by any of these models is the shift from winter snow to winter rain at high elevations, and the shift toward earlier dates of snowmelt (e.g. Barnett et al., 2008). As less precipitation falls as snow and that snow begins to melt earlier in the year, available water resources will diminish, even if PDSI and soil moisture do not change significantly. Taking all of these factors into consideration, we can say with moderately high confidence that over the past 50-60 years, drought has increased on a global scale. It's only a question of how much.

Despite the conflict with Dai (2011), Sheffield et al. (2013) did not entirely negate their conclusions regarding global drought. It is apparent from Figure 6 that the last three decades were characterized by more extensive drought than from 1950–1977, both in terms of PDSI and total land area in drought conditions. When I plotted the revised data myself (the red line in Fig. 6a), I obtained a downward (drying) trend, which is statistically significant at 99.4% confidence. Therefore, it is important to note that the title of Sheffield et al. (2013)—"Little change in global drought over the past 60 years"—does not mean "no change in global drought".

The most important revision by Sheffield et al. (2013) is that oversimplified calculations of PDSI resulted in an overestimate of drought response to global warming and, therefore, an overestimate of future drought risk from climate change. One key difference (overlooked by Dai, 2011) is the cooling effect of evaporation on air temperatures over land. Like a giant air conditioner, enhanced evaporation works as a negative feedback that slightly mitigates rising air temperatures. Amid the academic controversy, however, these authors worked together on a more recent synthesis (Trenberth et al., 2014) that affirmed drought has and will increase in response to global warming, though the response is more complex and less uniform than previously stated (Fig. 7).

Figure 7: Modeled reconstructions of global drought from historical data,
according to Trenberth et al (2014). Note the downward (drying) trend.
Three out of four global drought reconstructions by Trenberth et al. (2014) indicate that drought has become more prevalent over the land surface since global temperatures rose significantly in response to greenhouse-gas forcing. This conclusion is similar to Damberg and AghaKouchak (2013), who also noted reconstructed a trend toward enhanced drought (though their trend is statistically significant only for the southern hemisphere and individual watersheds on land). The initial predictions by the IPCC assessments, as well as Dai (2011) have been refined, but not negated.


Despite existing uncertainties in quantifying the response of drought to global warming, whether on a regional or global scale, the general consensus is that drought has already become more extensive and severe, and that future warming will only exacerbate the current situation. This relationship is more dreary from a human perspective, since growing population will only increase water-resource and agricultural demands, and no studies imply a wetting trend. Although we have much to learn about how global warming impacts the hydrological cycle, Dr. Wile's skepticism is premature and misguided, at best. Perhaps the best indication of this lies with the fact that none of the researchers cited (Dai,  Trenberth, Sheffield, Damberg, Hao, AghaKouchak, McCabe, Barnett, or their co-authors) share Dr. Wile's skepticism regarding global warming.

And neither do I, but I'm just a lowly paleoclimatologist. ;)

Note: This controversy has reached the Senate floor in Washington D.C. as well. Go here for a interesting discussion on the misperceptions of what climate scientists are/are not saying regarding global and regional drought.