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

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Sunday, February 20, 2011

Review of Chapter 6 – The Geologic Column, from 'Evolution Exposed: Earth Science'

Since I have already commented at length on the nature of the geologic column—how it was constructed, correlated, and dated—I will try not to repeat myself here. I am interested, rather, in defending a number of geological concepts that were criticized by Mr. Roger Patterson in Chapter 6 of his book Evolution Exposed: Earth Science, which was recently published online by Answers in Genesis. Therein, Mr. Patterson also offers a young-Earth alternative to geological concepts found in popular Earth Science textbooks. By way of preface, I sympathize with Mr. Patterson’s passion for improving standards in education and his eagerness to encourage critical thinking in the classroom. In my own high school biology classroom, I raised challenges to the teacher with regard to Earth history, common descent, and the geologic column. Though I have since answered those questions myself, it was this sort of critical discussion (albeit uncomfortable for most teachers) that inspired me to further pursue studies in the natural sciences. Nonetheless, I believe critical thinking can be encouraged without promoting a false dilemma between ‘young-Earth Christianity’ and ‘old-Earth Secularism’. Moreover, a healthy discussion is only stifled by the use of bad arguments on either side, and I believe that in an effort to undermine traditional Earth-science textbooks, Mr. Patterson cites a number of invalid arguments from various other young-Earth authors.

“Brute facts are mute facts”: interpreting the geologic column

Before delving into the geological details, Mr. Patterson reminds his readers that the facts “must be interpreted”, and he is right. Since geology is most commonly a hermeneutic science—interpreting historical data from natural (as opposed to artificial) experiments—geologists are well aware of the importance of starting assumptions. Of course, geologists are still human, and many modern debates (such as the nature/existence of mantle plumes) are at times driven by a geologist’s personal desire to corroborate his/her model of how things work. While bias can prolong a debate or the lifespan of a failed paradigm, however, it cannot survive in the research community if contradictory evidence mounts or another model better explains the data. When Mr. Patterson likens the debate between young-Earth creationists and “evolutionists” to a difference in starting assumptions, he not only oversimplifies the discussion (young-Earth advocates have not addressed a majority of the data), but misrepresents the nature of scientific evidence. “Billions of years” is not a starting assumption by anyone in the sense that geologic evidence is interpreted to support it (neither is an initial molten Earth, for that matter). Rather, it is the concluding interpretation of geologists assuming the validity and constancy of physical laws.

Before moving on, I would point out that Mr. Patterson overlooks the relevance of another hermeneutical science: biblical exegesis. He insists that when geologists try to reconstruct Earth history, the “real difference comes down to interpreting the evidence based on man’s understanding of billions of years, or using the Word of God as a starting point.” In essence, his pairing of “billions of years” and “Word of God” on mutually exclusive terms works to convince the reader that the debate is about philosophical authority alone. But the idea that the author(s) of Genesis 1–11 described a sudden appearance of Earth several thousand years ago is an interpretation of the textual data, and is contingent on a number of assumptions that play into the exegesis of the passage. One could reverse Mr. Patterson’s dichotomy by phrasing it this way:

The real difference comes down to interpreting the evidence through an understanding that God’s power and divinity are revealed in His creation (Rom. 1:20)—whose vastness, antiquity, and natural order reflect its Maker—or limiting the message of Genesis through lexical absolutism, demanding that science concord to man’s cloudy understanding of scripture, and derogating the wise providence of God by arbitrarily invoking miracles in history to explain contrary data.

By associating an old-Earth approach with a God-honoring hermeneutic—and the young-Earth approach with man’s cloudy judgment—one can induce favor from the target audience without having to demonstrate his/her position. Granted, Mr. Patterson’s focus in this chapter is not exegetical, but his choice of wording is potentially misleading to the otherwise inquisitive reader.

Uniformitarianism, and measuring geologic rates in the past

Young-Earth creationists commonly misunderstand the concept of uniformitarianism, and strive to present it as antithetical to their own interpretation of Earth history. In short, uniformitarianism is the two-fold, guiding principle in geology that: 1) physical laws have remained constant throughout time; and 2) past geologic events should be interpreted in light of known, modern processes when possible. Until recently, most young-Earth researchers have upheld (1), and I would argue that all geologists (“Flood geologists” included) would uphold (2) in principle. Although most young-Earth advocates claim adamant opposition to uniformitarianism (Mr. Patterson terms it an “unverifiable assumption”), they regularly employ it within their own research (e.g. sedimentary structures, sorting of fossils, erosional features, etc., all of which are interpreted through modern processes by adjusting variables like water depth/velocity). The confusion is a result, I believe, of their general disdain for Charles Lyell—whose contributions to geology resulted in a mainstream shift away from Noahic interpretations of sedimentary strata—but without discernment that Lyell’s Steady-State Earth hypotheses do not constitute uniformitarianism.

Failure to understand the definition and application of uniformitarianism can result in misguided accusations against conventional geological research. Mr. Patterson claims, for example, that “there is no absolute way to measure rates at which past events happened,” but the statement is demonstrably false, or at least demands an unrealistic criteria for scientific investigation. Consider two natural processes: tree growth and stalagmite formation. By studying the environmental factors that affect the pattern of tree rings, dendrochronologists have developed effective methods to interpret growth rates of individual trees—methods that can account for anomalies like forest fires, etc. that suspend or augment growth. Radiocarbon dating of individual tree rings provides an independent check on the interpreted ages. Consequently, scientists can use these data to measure growth of individual trees, forests as a whole, or even rates of sedimentation and mass wasting in the surrounding soil (e.g. soil creep on a hillside). In a cave system, slow dripping water precipitates carbonate and sulfate minerals to form magnificent structures (called speleothems). Paleoclimatologists are particularly interested in this process, because individual laminae of stalagmites record the chemistry of the water at the time of mineral precipitation (and hence information about the climate).

But how do we know how rapidly the stalagmite grew?

We must answer this question to assign a meaningful date to each lamina in the rock. From Mr. Patterson’s comments (he calls uniformitarianism “the doctrine that present-day processes acting at similar rates as observed today account for the change...in the geologic record”), you might think the rate is simply assumed to be similar to modern, observed values. In other words, one would measure the current rate of growth and just extrapolate back in time. But the rate of growth is different for each stalagmite, and can vary substantially within a single stalagmite, depending on the climate history. Therefore, paleoclimatologists use the Uranium-Thorium (U-Th) method to date laminae along the growth axis, and interpolate the values between points. [Theoretically, one could date every lamina, but at ~$500 per date, such would be fiscally irresponsible!] Like the radiocarbon method, U-Th is most accurate for young samples (less than 10,000 years old), but is reliable to ~500,000 years in many cases. Furthermore, it can be checked against historical (eyewitness) accounts of climate events in the region.

So in one sense, Mr. Patterson has a point: we cannot go back in time and directly measure rates of geological processes. On the other hand, we can apply the scientific method to interpolate (not extrapolate) the rate of processes in Earth history. I emphasize the scientific method here, because our interpretations can be falsified or verified through independent means. So what is the difference between the examples above and the approach of young-Earth researchers? Mr. Patterson will later explain that a significant portion of the geologic column was laid down within a year during the Flood, and dividing ‘how much’ by ‘how long’ gives you a rate. He applies a categorical distinction because in his eyes, God is the eyewitness of Earth history and has revealed certain events in scripture. The distinction is unwarranted, however, because according to the same scriptures, “The heavens declare the glory of God; the skies proclaim the work of His hands. Day after day they pour forth speech; night after night they reveal knowledge...they use no words...yet their voice goes out into all the Earth...” (Psa. 19:1-4) and “since the creation of the world God's invisible qualities...have been clearly seen from what has been made...” (Rom. 1:20). In other words, our witness to past geological events (and, consequently, the providential acts of God) is also written in the rocks, and disagreement between the two should cause us to reconsider our fallible interpretation of both.

Nicholas Steno and the principles of stratigraphy

Whether or not you are a geologist, I would recommend the story of Nicholas Steno’s contributions to science. First, Steno reasoned that fossils are the remnants of past life forms, based on the similarity of fossilized shark teeth to those of modern sharks. His conclusion was met by an important problem, however—namely, that one must account for how a solid (fossil) can appear inside of another solid (rock). Steno solved the dilemma by proposing that certain rocks could be formed over time as particles (mud, sand, and fossils) settled out of a water column (i.e. sedimentary processes). He employed this interpretation of sedimentary rocks to develop a set of principles for interpreting the relative history of rocks in contact with one another and geologists use those principles to this day.

When Nicholas Steno published his principles of stratigraphy in the early 17th century, he argued that fossil-bearing rocks may have been the result of Noah’s flood, inline with the available knowledge about Earth history. But consider Mr. Patterson’s description of Steno’s work:

“[Nicholas Steno] actually based his reasoning on the biblical account of the Flood and accepted that the earth was only about 6,000 years old—a Bible-believing creationist laid the foundation for modern geology!”

Steno may be rightfully credited with laying some important foundations for modern geology, but the statement above is somewhat misleading. First, Steno actually applied the yet-undefined principle of uniformitarianism to reach his conclusions about geological processes. He did so by interpreting the rocks in light of known, modern processes, and assuming the constancy of natural laws. The biological origin of fossils and ‘Principle of Superposition’ are not the necessary logical conclusions from the Flood story, and so many naturalists in the early church did not hold the same opinion about fossils and geological strata. While Steno’s acceptance of the Flood story as a global account caused him to interpret rocks in light of that event, we should not misinterpret the process he utilized. Later geologists, including Christians, used Steno’s principles to demonstrate that the Flood could not have been a global event. Their disagreement was not a matter of starting assumptions, but the result of having more data available. In short, Steno contributed much to science by remaining faithful to both witnesses to nature and following the evidence.

From index fossils to millions of years

I have described elsewhere the use of index fossils and radiometric dating methods to construct the geologic column, so I only wish to comment on a few of Mr. Patterson’s thoughts. Keep in mind that index fossils are those that are found 1) across a wide geographic area, 2) are easily distinguishable from similar species by their physical morphology, and 3) have a relatively short life span within the geologic record. In other words, index fossils are named as such for their ability to assign rocks to specific time periods in Earth history. Despite the considerable success of geologists in using index fossils to guide their research (from stratigraphy to paleoceanography to petroleum exploration), Mr. Patterson argues against their viability for a number of reasons.

“Slight differences in shell shape or structure are used to assign the shell to a new species, despite the variation apparent within a single living species today.”

In the fossil record, organisms can be distinguished only by their physical characteristics, in contrast to the modern setting, where species are differentiated on biochemical, genetic, and other factors. Paleontologists recognize this, and typically use the term morphospecies to describe a unique fossil form. A morphospecies is not intended to be the taxonomic equivalent to modern biological species, hence it matters not whether the observed variation might have occurred within a single species.

“Another problem with index fossils is that, rather than being proof of evolution, evolution is already assumed to have occurred.”

In fact, the use of index fossils has almost nothing to do with evolution. One must only assume that fossil assemblages from the rocks of interest are representative of life at the time of deposition. Whether those life forms got there by evolutionary diversification, divine creation, or by alien transplant makes no difference in practice. Index fossils are not used, therefore, as proof of evolution. On the other hand, the pattern and occurrence of index fossils does corroborate macroevolutionary theory (i.e. evolutionary theory predicts diversification into empty niches after extinction events, inline with what is observed in the fossil record).

“The idea that life became increasingly complex over time...was used to analyze the fossils in the rock layers. It was assumed that by identifying the order of fossil succession, the layers could be correlated from one region to the next. Index fossils are still one of the major indicators of the age of a given layer.”

Unfortunately, the line of reasoning within this paragraph is backwards, as it should read: the ability of geologists to correlate the order of fossils from one section of rock to the next gave way to the idea that life became increasingly complex over time; thus index fossils became one of the major indicators of the relative age for a given rock sequence.

Early on, geologists attempted to calculate the absolute age of sedimentary rocks through a variety of extrapolations, but the advent of radiometric dating surpassed all previous attempts both in accuracy and elegance. By the time any radiometric dates were assigned, geologists had already determined the relative age of rocks and assigned boundaries to geologic periods based on the fossils. In the past 70 years, paleomagnetism, astronomical cycling methods, and chemostratigraphy have provided independent checks on both relative and absolute ages (see here for further discussion).

“If the ages determined for a fossil do not fit the presuppositions, the ages are often massaged until they fit within evolutionary thinking.”

All Mr. Patterson has described here is the fact that radiometric dating is not a perfect process, and a valid interpretation must fit the overall picture. In other words, anomalous data cannot be used to overthrow the entire paradigm (this is true in all academic disciplines). In the case that a radiometric date contradicts the expectations from other geological data (e.g. fossils), the scientist should reconsider his/her interpretation of both, and repeat the experiment. Imagine that one day you bought a new bathroom scale, took it home and weighed yourself, only to find that you are suddenly 50 pounds lighter than expected (or estimated from your height and stature). What do you do? To start, you could formulate multiple competing hypotheses and design an experiment: either a) you lost a significant amount of weight without noticing, or b) the scale is broken or badly calibrated. Of course, the simplest way to resolve the matter is by attempting to falsify (b), in which you could weigh yourself on several other scales. This is not a case of “massaging” the data, but of using the scientific method to ascertain the truth and resolve apparent contradiction.

As an aside, if Mr. Patterson wants to properly challenge the interpretations of radiometric dating, he must propose or cite an alternative understanding that can be tested scientifically. Whether or not one accepts the underlying assumptions of biostratigraphy, the fact that it accurately predicts the results of radiometric dating must be reconciled with any competing model.

The Grand Canyon

Many people find it peculiar that young-Earth creationists so commonly use the Grand Canyon to explain Flood geology. I would suggest the reason is that the Grand Canyon is one of the simplest places to understand the geologic column in general, and perhaps the only place to understand the geologic column from a young-Earth perspective. The ‘Great Unconformity’ at the base of the Grand Canyon is presented as evidence for the onset of the Flood, while thick bodies of overlying sediments are arranged in a rather simple, ‘pancake-layer stratigraphy’ that is said to represent repeated transgression of the Flood waters over the continent. Despite numerous problems with this model, the presentation is very effective to those not familiar with the details of Grand Canyon geology. At the same time, anyone familiar with the geological complexity of strata outside of the Colorado Plateau will recognize that this interpretation cannot be applied to a majority of locations on Earth, and so young-Earth publications rarely speak about the geology of...well, anywhere but the Grand Canyon.

To cite a few brief examples, I want you to consider these cross-sections from western Wyoming, Virginia, Nevada, and Spitsbergen. Each link corresponds to a geologic cross-section from that region that is available online, so you can follow along.

The cross-section from Wyoming illustrates what is called a ‘fold-thrust belt’, which resulted from several mountain-building events that compressed the crust and sedimentary rocks until they were thrust on top of one another. For those of you in northern Utah, you can see a similar cross section firsthand by driving through Ogden Canyon. As you can see from the image, many of the faults (solid, near-vertical lines) are cut off by other faults, which means that sediments had to be laid down and turned into rock before the next faulting event occurred (see the bottom of the image between the words “Darby Thurst” and “Absaroka Thrust” for one example). If the sediments were unconsolidated (still soft) during faulting, or saturated with water, then they would have acted as a liquid and the faults and fold structures would not be preserved today. The structural complexity of the region provides sound evidence that a great amount of time was required to produce the local stratigraphic arrangement. Not shown on the regional cross-section (the scale is too large) are numerous ‘syntectonic’ deposits. These rock formations are conglomerates that formed during mountain-building, and contain weathered fragments of the older sediments, including limestone, mudstone, and quartzite boulders. Once again, if all of these sediments were laid down within a year (or even within several thousand years), then the underlying sediments would have been too soft to form the gravel and boulders (especially quartzite) now found in syntectonic deposits.

The cross-section from western Virginia shows a similar arrangement of folded sediments accompanied by faulting. One difference is the near vertical orientation of rock layers seen on the right side (near Richmond). Now the question is, how long does it take, not only to turn such massive layers of rock on their side, but to erode a majority of the rock, leaving behind the landscape now seen near Richmond? Mr. Patterson and others might be tempted to say that receding Flood waters could do the job in no time, but no evidence of rapid erosion (such as large canyons, or scablands) exists on the eastern plain. Instead, the region is characterized by gentle hills and mature river systems.

This image shows only the Mississippian to Permian-aged rocks in the Great Basin, so I would only point out a couple of details. First, the Ely and Pequop limestone groups transition into shale units to the west. This lithologic pattern is similar to what is found in a modern continental shelf to slope environment (consider the eastern coast of Mexico as one moves toward the Gulf). Moreover, the fossils, sedimentary structures, and chemistry of the rocks are consistent with such an environment. Secondly, note the shape of the Great Blue Formation. The reason it is thicker than adjacent units is that it contains a reef/sandbar geometry, where sedimentation was higher than toward the coast or basin. Again, the fossils, sedimentary structures, and chemistry are consistent with this interpretation. None of these rocks show evidence of rapid deposition, but each contains remnants of a past, healthy, marine ecosystem like those seen today. So the most parsimonious interpretation is that these rocks were deposited over long periods of time when the see covered much of the western United States.

In this image, you can see a transition from shallow-water, coastal sediments (left) to deep-water, continental slope deposits (right). The ancient, submarine topography is evident from the shape of the unconformities (bold lines). Fossils (oysters), sedimentary structures (cross-bedding, lamination, etc.), and lithologies (rock types) are consistent with the modern setting and show no evidence of rapid deposition beyond the occasional storm deposit or turbidity flow. Furthermore, ancient channels (note the features labeled ‘tidal inlet’) are preserved in the layers, and suggest that long periods of time were available to erode the submarine landscape before the sea transgressed.

Grand Canyon Formations — evidence of global catastrophe?

Mr. Patterson reflects the sentiments of other young-Earth researchers in his description of the rocks found at Grand Canyon:

“The layers exposed in the walls of Grand Canyon and in the Colorado Plateau region provide evidence of a catastrophe that must have covered at least the entire North American continent. The layer known as the Navajo Sandstone contains minerals that were eroded from the Appalachian Mountains. A river is used to explain this in the uniformitarian model, but a global Flood makes more sense of the evidence. The Tapeats Sandstone contains large boulders and was deposited in storm conditions over an immense area of north America. The Redwall Limestone extends from the Southwest to Pennsylvania and Tennessee—obviously deposited as the result of a massive catastrophe.”

I understand that the scope of Mr. Patterson’s book does not permit him to detail his reasoning as to how the “global Flood makes more sense of the evidence”, but the few points above warrant some discussion. First, it is not surprising, under the “uniformitarian” model, to find minerals in a desert dune deposit from long distances. One of the characteristics of the Navajo Sandstone is that the sand is very well sorted—this indicates the grains had time during transportation to homogenize. Prevailing winds over a continent (such as in northern Africa today) accomplish this task efficiently. Rivers can do the same. Consider, for example, the Arkansas River, which carries sediment from the Rocky Mountains to the Gulf of Mexico (via the Mississippi). Second, boulders in the Tapeats Sandstone are derived from the underlying Precambrian rocks. This suggests that Precambrian sediments were buried and lithified before they were eroded and deposited within the Tapeats, again consistent with the “uniformitarian” model. Finally, the geographical extent of the Redwall Limestone is not necessarily indicative of a “massive catastrophe”. In fact, it is simply impossible to deposit such quantities of carbonate rock over a large region without significant incorporation of sand, mud, and clay material.

Paleogeographers use the magnetic signature of rocks to infer the latitude at time of deposition. Along with clues from the sedimentology (fossils, structures, etc.), they can create ‘paleomaps’ of the continents at a given time. Click here to see a reconstruction of North America during the Mississippian (340 m.y. ago), when the Redwall Limestone was being deposited. Sea level was higher, and the continents were lower, so the ocean covered much of the continent. This image represents the combined work of hundreds of geologists that study Mississippian rocks, and provides an interpretation that explains all relevant data—from the type of rocks deposited, to the fossils they contain, to the chemistry they record, to the radiometric dates of minerals contained within the rock. There is simply no reason to believe the Redwall Limestone was deposited amid a global catastrophe.

Concluding remarks

In an effort to spark critical discussion of conventional geologic topics presented in school textbooks, Mr. Patterson raises a number of ‘plausible-sounding’ objections from young-Earth researchers. When examined in detail, however, the objections find little support in the geosciences. In fact, Mr. Patterson’s main counterexample—the Grand Canyon—only substantiates the concepts found in those textbooks.

In line with many Flood geologists, Mr. Patterson does not accurately describe the process by which the geologic column was constructed. Moreover, he misinterprets the concept of ‘uniformitarianism’ and overlooks the fact that even young-Earth geologists apply this principle in their own research. Consequently, I think it is inaccurate to refer to the “uniformitarian” model over against young-Earth claims.

Although I sympathize with Mr. Patterson’s passion for education, and agree that more critical thinking is needed in the classroom, I sincerely believe that the young-Earth presentation of the geologic column is not rooted in scientific observation and may stifle much-needed inquiry from students regarding the evidence that actually exists. For the sake of accountability on both sides of the discussion, I hope that I have responded fairly to his claims and that he might consider my criticism as amiable confrontation out of love for the truth.

Saturday, February 12, 2011

Direct radiometric dating of dinosaur bones using the U-Pb method, and ICR's attempt to avoid the issue

Well, they've finally done it. In a Geology article published last month, Fassett et al. (2011) described their application of the Uranium-Lead (U-Pb) radiometric dating method directly to fossilized dinosaur bone. In addition to applying a known dating method to a completely new type of sample, the authors' specific goal was to demonstrate from independent evidence that dinosaur bones found in an early Paleocene sandstone were not inherited from older strata. Why is this important? For two reasons. Until now, only circumstantial evidence has been available that any (non-avian) dinosaur taxa survived past the Cretaceous-Paleocene boundary (65.5 million years ago), but the 64.8 (±0.9) Ma age obtained from their 'bone in question' provided a powerful argument that the creature lived after the global extinction event (albeit less than 1 million years after and in a single locality). The second reason is that the geologists were able to date directly something other than an igneous rock, and surely this has never been done before...right?

If you learned about radiometric dating from a textbook in school (like me), then you were likely taught geochronology as it was ~60 years ago, and in a simplified format: igneous rock cools to form crystals, single parent decays into single daughter element, crystal acts as a closed system, initial daughter concentration is known, decay rate is known and constant, etc. There is nothing wrong with this picture, and these principles are important in many radiometric dating methods employed today. But for anyone interested, geochronology has come a long way since its original applications. Scientists have since been able to place direct radiometric dates on lake sediments, calcite cements, black shale, speleothems (i.e. cave rocks), fossilized teeth, detrital minerals in ancient sediments, coral reefs, and even ground ice! These specimens range in age from Proterozoic (1.8 billion-year-old black shale) to present day (modern lakes, caves, and permafrost), and are commonly dated through multiple independent methods.

On the other hand, it would be unfair to give anyone the impression that U-Pb dating of a dinosaur bone is no big news. When dealing with non-igneous samples, many of the basic assumptions (mentioned above) go out the window and so the method becomes very complicated. For example, complete fossilization of the dinosaur bone may have taken several thousand years (or more) to complete, so the "age" of the bone is not the same across the whole sample. The apparent age depends on current uranium and lead concentrations, the former of which was incorporated into the bone as the original bone material was replaced by silica. Over time, both parent and daughter can be lost through fluids in a porous sandstone, or uranium can be added through further permineralization. In other words, it must be assumed that your 'crystal' acts as an open system and that many of the dates can or will be wrong. Normally, U-Pb data are plotted on a concordia diagram to quantify the loss of uranium or lead, but since dinosaur bones do not act (geochemically) like a magma chamber and the fluid chemistry is variable over time, there is no easy way to detect such disturbances since the time of deposition. Instead, the authors plotted U-Pb ages vs. the ratio of radioactive uranium to stable lead (238U/204Pb) to look for trends that would indicate uranium enrichment or lead loss (both of which can make the sample appear younger). In the first sample, they found good evidence that uranium enrichment had occurred (near 20 Ma) and that various diagenetic processes produced a scatter in U-Pb ages throughout the bone, while the second sample was less disturbed and yielded more consistent U-Pb ages. Available radiometric and geomagnetic dates for the rocks containing the fossils agreed very well with the obtained U-Pb age of each bone sample once diagenetic effects were accounted for (73.04 Ma vs. 73.6 Ma for Sample 1; 65.1–64.0 Ma vs. 64.8 Ma for Sample 2). In short, the authors' results are very encouraging for both geochronologists and paleontologists, and provide good evidence that the dinosaur bones were 73.6 and 64.8 million years old, respectively.

Of course, not everyone welcomed the study with enthusiasm, as elucidated by Institute for Creation Research (ICR) science writer Brian Thomas's review of the study. Therein, he claimed that the dino-bone ages were "not only the result of a broken radioisotope system," but were "contrived to agree with previously assigned dates for the samples." He advised the authors to search for remains of collagen, which could then be dated by the radiocarbon method, to prove that the samples were multimillions of years old. However, he does not expect the advice to be heeded, since it may rather provide evidence that the bones "are not millions of years old" and might "call the whole evolutionary picture into question, and...offer evidence for a recent creation."

Perhaps that's a valid question. Why not "take the scientific high road to legitimacy", as he puts it?

Despite Mr. Thomas's strong words, I think there is good reason that his critique will fall on deaf ears. First, his description of the method practically mirrors the wording of a Science Daily news report found here. Coupled with a handful of inaccurate statements about the technique—"an igneous rock...unlike sedimentary rock...has been considered 'datable' because the relevant isotopes are locked up in its tiny crystals", "radiodating", "it was taken on faith that the data indicating a younger age do not represent the real age"—, Mr. Thomas's report indicates that he is not very familiar with the Uranium-Lead system (beyond the basics). Second, he claims that samples were hand picked to match up with the "known" date of 64 million years, obviously missing the fact that two samples were dated: the first was bone from a well-dated horizon (73.04±0.25 Ma) and worked as a control sample; the second was a bone from a horizon with a range of ages (65.1–64.0 Ma, based on magnetostratigraphy), and was suspected to be older than the sedimentary rocks containing it (i.e. an old dinosaur bone washed into new sediments). While the first sample yielded a scatter in U-Pb ages (many of which were younger than expected), ages obtained for the second sample were all statistically within the age of the bed, and no "hand picking" was necessary. Third, he defers the discussion to a review article of the RATE team, which apparently shows that "evidence has mounted that radioisotopes underwent a period of radical acceleration of decay in the past." As discussed last week, this supposed evidence is not only highly circumstantial, but surrounded by poor and dishonest scientific practice. Fourth, he challenges the authors to search for collagen remains in the bone, apparently overlooking the fact that each bone sample was already mapped by a Scanning Electron Microprobe (SEM). In other words, if the bones contained any carbon-rich (organic) components, the authors would have reported it, and their results would be in Nature or Science, not Geology.

Most importantly, Mr. Thomas does not offer an alternative explanation for the geochronological data, but only claims that the system is broken. One must ask, however, why the ages agree at all if the system is simply broken? The sandstone containing the first bone sample was dated by a sanidine mineral from a nearby volcanic ash, using the 39Ar/40Ar method, while the range of expected ages for the second sample is the result of dating the ocean floor through K-Ar and other methods. In a young-Earth model, how are these processes even remotely linked? If the multimillion year ages are the result of accelerated nuclear decay in the past (an absurd scenario for multiple reasons), why would they even be remotely concordant across sample types and methods, let alone within one standard deviation?

I would suggest that Mr. Thomas simply does not have an explanation, and therefore must hope that his readers will not pick up on his false accusations about "hand picking" data. For in the world of young-Earth creationism, evidence of the Earth's antiquity simply cannot be accepted. It truly is that simple.

References Cited:

Fassett, J.E., Heaman, L.M., Simonetti, A., 2011, Direct U-Pb dating of Cretaceous and Paleocene dinosaur bones, San Juan Basin, New Mexico: Geology, v. 39, p. 159-162.

Sunday, February 6, 2011

Clearest evidence that the Earth is 6,000 years old: helium diffusion in zircons

By way of preface, I do not intend this post to be a thorough scientific discussion about helium diffusion in zircons. If you are already familiar with the topic, that’s great. But in case you don’t consider yourself “geology-savvy”, or simply have no interest in understanding the scientific argument put forth by Answers in Genesis (AiG) and the Radioisotopes and the Age of The Earth (RATE) team, I would encourage you especially to read on. In particular, I want you to consider whether AiG functions as a scientific research institution, given the manner in which they have promoted the results the study below as compelling evidence for a young Earth. My critique today is not so much about the rocks, the data, or even the interpretations of those data—it is about AiG’s failure to work according to the scientific method. By ignoring healthy criticism of their research and avoiding followup experiments, they have foregone a valuable opportunity to take part in the scientific community and instead reduced themselves to dogmatism. How? Let’s take a closer look.

What is the clearest evidence that the Earth is less than 10,000 years old?

If you perform a quick search for the answer online, whether on a standard search engine, young-Earth ministry pages, or even YouTube, you will no doubt come across a study entitled “Helium Diffusion Rates Support Accelerated Nuclear Decay”, which was updated and reposted by Answers in Genesis last week. The authors analyzed samples of zircon minerals from a well bore in New Mexico as part of an ongoing project (the RATE team) to test the validity of radiometric dating techniques. In essence, the study argues that although Uranium-Lead (U-Pb) dating of the zircons suggests that ~1.5 billion years worth of uranium decay has indeed taken place, additional evidence shows that helium (a product of radioactive decay of uranium) has only been diffusing out of the minerals for about 6,000 years (±2,000 years). To account for the wide discrepancy in age estimates, the authors propose that accelerated nuclear decay occurred early in Earth history—that is, about 6,000 years ago. This phenomenon would undermine the validity of radiometric dating techniques, since those techniques assume the rate of radioactive decay to have been constant over time. According to the authors, one must consider the possibility of a recent creation to make sense of these contradictory geologic “clocks”.

Details of this study have not only been published privately in the young-Earth community (in books, journals, and online responses to critics), but were presented in the form of a poster at an American Geophysical Union conference (Humphreys et al., 2003). Since that time, numerous critics have raised concerns about the methodology of Dr. Humphreys and the RATE team, even going so far as to accuse them of academic dishonesty (“fudging of data”). While members of the RATE team have not simply ignored their critics, the fact that AiG continues to publicize the study with very few changes from 8 years ago implies that the authors consider the counter-arguments sufficiently rebutted. On the one hand, this may invoke confidence in the results of their study: why fix something that isn’t broken? I will argue, however, that the response of the RATE team rather reveals the anti-scientific character of researchers at Answers in Genesis.

The reason the study remains popular and the reason I won’t detail the scientific problems with it are one and the same

Before you read any further, I would strongly encourage you to look at the recently published summary here. If you prefer a succinct graphical presentation, you can also view the AGU poster here (opens a PDF). I’m not asking you to understand all the science, or even read through the whole article. Just take a couple minutes to skim through the methodology and graphs, and return here when you finish.

Now, what was your immediate response? Were you impressed by the presentation of data, numerous equations for the diffusion model, photos of the zircons? To be fair, it appears at first glance that Dr. Humphreys and the RATE team have done their homework, and are capable of conducting geological research. When the first report was published some 10 years ago, I immediately thought: “Well, I don’t know how they did it, but it’s obvious these guys know what they are doing!” In the years to follow, AiG published responses by members of the RATE team to their critics, and made it seem that everyone was desperate to discredit the study, but to no avail. To be honest, I didn’t really understand the questions back then—or the answers for that matter—but as far as I could tell, Dr. Humphreys was prepared for the criticism.

So the more important question becomes, did you understand any details of the article/poster beyond their conclusion regarding the age of the Earth? Even if you can explain the use of helium concentrations in U-Pb-dated zircons, could you explain Dr. Humphrey’s method of predicting helium diffusivity given a 6,000-year timescale? If you agree with the RATE team’s interpretation of the data, can you explain the strong points in the study, and detail where the uncertainties lie and what assumptions were made? If you disagree with the RATE team’s interpretation of the data, can you suggest how to properly understand them, or cite the weak points in their study?

The reason I pose this seemingly rhetorical string of questions is simple. I am willing to bet that if you presented Dr. Humphrey’s research in detail to the geology department at any university, you would find a handful of geologists at most that would be able to follow the arguments without spending several hours reading up on the methodology. The modeling of helium diffusivity in zircon grains is a very complicated, math-intensive process that requires a particular expertise to apply properly. This method was developed only recently (hence the lack of data before 1999), and has been studied by a relatively small number of researchers over the past 10 years. The results can be extremely useful to geologists, and so hundreds of published studies have made use of helium data from zircons, but very few people are familiar with the laboratory procedure.

Unfortunately, the technical aspect of the RATE team’s helium diffusion study works very well in their favor. If most professional geologists would have trouble following along, what will the average AiG reader take from the study besides unwarranted confidence in young-Earth creationism as a valid scientific endeavor? At the same time, the average critic of AiG is left scratching their head in search of a good reason to cast doubt on the results. Consequently, AiG can knock down the endless string of bad arguments to appear victorious before their audience.

Answers in Genesis has not managed to stump everyone, however, and several experts in the discipline have provided lengthy responses to their work. For those interested, Dr. Gary Loechelt published a semi-technical discussion of each model here, while a PDF of his full technical paper is available here. Therein, Dr. Loechelt’s offers constructive criticism based on his expertise as a researcher in material sciences. His analysis is eloquent and fair, focusing on the science behind Dr. Humphrey’s interpretation of the data rather than simply dismissing him on account of his association with AiG and the Institute for Creation Research (ICR). University of Kentucky geologist Dr. Kevin Henke published an even lengthier response here, offering a more in-depth analysis of the geological aspects of Dr. Humphreys’ original paper. Although some would find Dr. Henke’s tone too antagonistic for comfort, he raises valid objections that could and should be incorporated to Dr. Humphreys’ ongoing research.

Between all the links above, there is little scientifically that I could add to the discussion. Although I have spent many hours improving my understanding of noble-gas diffusion through mineral solids (hours well spent, to be sure!), I do not have the expertise of the aforementioned researchers in this particular discipline, and summarizing their arguments here would miss the aim of my post, which is to consider AiG’s application of the scientific method.

The goal of the scientific method is to communicate the results

When I teach introductory geology, I make a point to inform students that above all, geologists are writers. A majority of any scientist’s time, in fact, is devoted to the publication of research through three steps: 1) familiarizing oneself with the research of others in the field; 2) detailing the results and interpretations of one’s own research (writing and publishing articles), so that the experiment can be tested or improved upon by anyone in the field; 3) refining the results and interpretations of one’s research (authoring a new research proposal) by considering the criticism of others. Steps 1 and 3 overlap to form a never ending cycle for the research scientist, but also connects him/her to the scientific community. Without this constant interaction, a scientist’s work is (practically speaking) invalidated, either through silence or through dogmatism. In the former, the scientist simply never publishes his/her research, so the result is the same as if he/she had never run the experiment. In the latter case, the scientist rejects both criticism and contrary data from fellow researchers, and never improves his/her experiment. Consequently, his/her results and interpretations have no impact on the scientific community at large.

Now, which of these scenarios best describes the actions of the RATE team? I would argue that Dr. Humphreys and others were familiar with the scientific literature, and published their results with sufficient detail that the experiment could be repeated. In other words, they had no problem accomplishing steps 1 and 2 above. Furthermore, their research was capable of producing scientific hypotheses regarding helium concentrations in zircons elsewhere, given a measured diffusivity. Thus they were in a better position than most young-Earth creationists before them, having a large audience and a valid means to take part in active discussion within the scientific community. All they needed to do was: 1) collect more data and report whether their model was consistent and predictive of scientific phenomena; 2) refine the model according to critiques by other experts in the field to determine whether such critiques were valid. It has been more than 10 years since the original report was published; what did they decide to do?

Response of the RATE team to the scientific community

To his credit, Dr. Humphreys has devoted much time responding to some of his critics. Neither he nor any member of the RATE team have, however, produced new data, collected new samples, or modified the original model to account for its admitted shortcomings. Instead, he has challenged others to publish their critiques in peer-reviewed journals. Given that his own research can not be found in a peer-reviewed journal, this seems an inappropriate challenge (publishing in a journal costs money, and this money is not well spent critiquing an unpublished model through an article that adds nothing to the research community). Nonetheless, both Dr. Loechelt and Dr. Henke have offered models for interpreting the data consistent with the conventional geologic timeline and posted them for public access. The response is exceedingly generous on their part, given the number of hours required to draft a monograph that adds nothing to their salary or resumé.

The RATE team concluded in their helium diffusion study that the “uniformitarian model” was off by a factor of 100,000 in predicting the observed diffusivity values. When challenged that his model was over simplified, Dr. Humphreys’ alternative tactic has been to respond that the assumptions he used were “generous to uniformitarians” and that it doesn’t help their case. In doing so, he has not only stifled the scientific discussion by taking a dogmatic stance, he has abandoned the scientific method completely. Here are a few examples:

1) Estimated Q/Qo values: the rate team reported ratios of the modern helium concentration to the total helium expected from 1.5 billion years worth of decay (Q/Qo). To calculate this value, one must assume or estimate the initial concentration of uranium in the mineral, since the decay of uranium into lead produces the helium. How is this done? Values reported by the RATE team were estimated based on the lead (Pb) content (the radiogenic daughter product), which was assumed to be constant between mineral samples (though the original formulas were not reported). Not only is lead heterogeneous in igneous rocks and minerals, but it can also diffuse out of the rock over time. Thus Pb concentration is not a viable proxy for the original concentration of uranium, and Dr. Humphreys knows this. Modern methods use the ratio of thorium to uranium (Th/U) for a more accurate estimation. The Th/U ratio is easy to analyze (and inexpensive), but even after 10 years, it has not been implemented into their model. Why? Dr. Humphreys notes that adjusting the value would “reduce the percentage retentions by only a factor of two or so” (Humphreys, 2005), implying that it still wouldn’t fit the “uniformitarian model”. That may be true, but what does it do to his own predictions? The estimated age of the zircons is no longer a tidy 6,000 years—it becomes much closer to ~20,000 years. Apparently, this is not acceptable to the RATE team (6,000 years has a special ring to it in the young-Earth community), and so they stick with the simpler interpretation (but have yet to publish exactly how those values were calculated in the first place).

2) Geometry of the zircons and grain boundary conditions: if you take a look at Figure 7 in the most recent article, it reveals another assumption in the RATE team’s model. Zircon minerals were assumed to act like a 30-micron sphere during diffusion, rather than elongated prisms as seen in Figure 1. Scientific models commonly use mathematical simplifications, for obvious reasons, when the results are relatively unchanged. Dr. Loechelt points out in his technical paper, however, that the chosen radius is too large to accurately represent a 75-micron zircon. Thus the RATE team’s model significantly underestimated the amount of helium that should still be present. Furthermore, the model assumed a helium diffusivity for biotite equal to that of zircon. Though Dr. Humphreys knows and admits the assumption is not accurate, he avoids dealing with the correction because it is “generous to uniformitarians”. In other words, the assumption further underestimates the amount of helium that should be present so that the RATE model no longer fits. If you combine the effect of geometrical and boundary condition factors, the RATE team’s prediction is incorrect by more than an order of magnitude, and they could no longer report a 6,000 year age of the Earth.

3) Geothermal history: the rate of helium diffusion in minerals is temperature-dependent. In other words, higher temperatures would have cause more helium to escape in the past (hence the lower concentrations of helium in the samples at greater depths). Dr. Humphreys assumed a constant temperature to calculate the “uniformitarian model”, even though a thermal history of the region is available and reveals the samples were at far lower temperatures for a majority of the past 1.5 billion years. Dr. Humphreys originally misread the thermal history, and said his assumption was again “generous to uniformitarians”. He has been corrected, but still refuses to work the real thermal history into his model. Why? Even if the “uniformitarian model” still fails to accurately predict the data, according to his own calculations, it is bad (and dishonest) practice to discredit a model that has no basis in reality.

But here is the better question: what kind of thermal history should Dr. Humphreys use for his own model? Would it be reasonable to assume a constant temperature through time? As the RATE team is aware, radioactive decay produces heat. Key to their model is the notion that 1.5 billion years’ worth of radioactive decay occurred sometime in the past 6,000 years (during Creation Week or the Flood). Without invoking a change in physical laws, such accelerated decay would have caused the rocks to melt and there would be negligible helium in them. However Dr. Humphreys chooses to deal with the problem, he is forced to abandon the scientific method without begging the question, since the results will always be “proven” by his assumptions—namely, that the rocks are 6,000 years old no matter what the data and models say.

Lapsing into dogmatism by refusing future work

A number of other improvements could be made to the RATE team’s model, such as using a multi-domain diffusion model (actually, this is probably the most important one), but in more than 10 years, almost nothing has been refined. More time has been spent arguing that the model cannot accurately predict a “uniformitarian” history of Earth, despite the publication of Dr. Loechelt’s alternative model that does. I think that given the budget and claimed expertise of AiG’s research team, a much simpler solution can be found.

Why not repeat the experiment?

What prevents the RATE team from collecting and analyzing new samples, even in collaboration with their critics, to demonstrate that a young-Earth model can better predict the data? The problem is neither money, time, nor incompetence—what is it? Answers in Genesis and the Institute for Creation Research have a golden opportunity to take active part in the scientific community, but have made every effort to avoid proper contact. Perhaps I am wrong, but I suspect they already know the results will not be in their favor. All one needs to do is perform a literature search for “helium diffusion in zircon” or “uranium thorium helium zircon” in scientific journals. Since the RATE team began their helium project, hundreds of articles have used helium concentrations and measured diffusivity in zircon to date thermal events in geological strata (buried layers of rocks). How many of these studies do you expect to be consistent with the RATE team’s estimate of 6,000 years?

Exactly none.

And so AiG will instead devote their resources to dogmatically defending a failed model in hope that their readers will not understand the science behind it. I imagine they will continue to publicize this study until another rigged experiment can be found. Until then, we can only scratch our heads and hope that people will pay closer attention to the most basic aspect of science: the scientific method.

References Cited

Humphreys, D.R., Austin, S.A., Baumgardner, J.R., Snelling, A.A., 2003, Precambrian Zircons Yield a Helium Diffusion Age of 6,000 Years: American Geophysical Union Fall Conference, v. 84, Abstract V32C-1047. (http://www.icr.org/pdf/research/AGUHeliumPoster_Humphreys.pdf)

Humphreys, D.R., 2005, Helium Evidence For A Young World Remains Crystal-Clear: http://www.trueorigin.org/helium01.asp