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

Never been here? Please read my guidelines and background posts before proceeding!

Wednesday, March 30, 2011

The Japanese tsunami and ICR's 'faulty' understanding of tectonics and uniformitarianism

The calamitous aftermath of the recent earthquake in Japan has, understandably, contributed to countless conversations concerning the proper charitable response, energy policy, and even the humbling power of nature. Nonetheless, I was admittedly surprised when Brian Thomas of the Institute for Creation Research (ICR) published an article entitled Japan Tsunami Demonstrates Destructive Power of Water, in which he conjured a peculiar analogy between those events and his version of the Noachian Flood. He summarizes the relationship as follows:

"If one relatively small earthquake-generated tsunami could cause this much damage in Japan, how much more damage would be caused by the barrage of tsunamis generated by continuous, worldwide earthquakes during the year-long Flood of Noah...?"

Some may question whether it is entirely appropriate to discuss the recent tragedy in light of an act of cosmic judgement, given that many are still in mourning for the losses. I would sympathize with such a reaction, even though I believe it is clear Mr. Thomas did not suggest any theodicean explanation for the events in Japan. That being said, I think it is still worth commenting on whether his proposed geological connection holds up. Do tsunamis hold the answer for interpreting the geologic column as a product of the Flood?

Tsunamis are necessary in a functioning geosphere

Natural disasters do provide an effective teaching tool in geology—albeit too 'close to home' for some—by placing a rather palpable face on otherwise abstract geological concepts. The recent tsunami and previous earthquakes off the coast of Japan are the inevitable result of subduction processes near plate margins. Thick, cold basalt of the Pacific Plate is currently sinking into the mantle, far beneath the eastern coast of Japan. The crustal rocks remain in contact, however, and since this is not a frictionless process, seismic events are frequent. At several miles' depth, the characteristics of the rock are such that significant strain (stretching) can build up, only to be released when it overcomes the shear strength of the rock. If that is not clear, imagine pulling apart opposite ends of a giant taffy bar. If the taffy is too cold (like "just out of the freezer" cold), then it will crack/fragment before splitting. If the taffy is too warm, then it will just keep stretching. Within a certain temperature range, however, the taffy accumulates strain until it snaps, releasing the stored energy all at once.

The magnitude of an earthquake (i.e. the amount of energy released) is a function of the potential strain that can build up before shear failure occurs. Following the taffy analogy, the maximum amount of strain depends on the surface area along a fault plane that falls within a particular temperature range (for silicate rocks, this can fall between ~300°C–600°C, depending on the composition). Suffice it to say that in subduction zones—where both the geothermal gradient (temperature change with depth) and fault dip are relatively low—the maximum potential strain is rather large. Consequently, some of the most violent earthquakes occur at plate boundaries where subduction is taking place.

Although the subduction of oceanic crust results in frequent natural disaster at Earth's surface, it contributes overall to the life of the planet. Subduction zones form island chains and mountain ranges (e.g. the Andes, Sierra Nevadas, Aleutians, etc.) and are concomitant with the creation of new oceanic crust at spreading ridges. Without this tectonic process, Earth's mountains would be free to erode more or less completely, to eventually fill the ocean basins. No subduction, no mountains and oceans. No mountains and oceans, no climate. No climate, no life.

Natural disasters and uniformitarianism

Mr. Thomas quotes Charles Lyell, who originally suggested "the present is the key to the past", to show that uniformitarianism has since accommodated catastrophes like tsunamis and large earthquakes when interpreting the rock record. I think Mr. Thomas would agree, however, that in geologic terms, natural disasters are "everyday natural processes." It is not as though Lyell would object in principle to the interpretation that a turbidite deposit represents a catastrophic, underwater density flow, or that a 5-meter thick lava flow must have taken millions of years to form. Modern geology's objection to Lyell deals rather with his 'big picture' application of uniformitarianism (a steady-state Earth), and is not relevant to the discussion.


Although the recent earthquake and tsunami in Japan was not the largest on record, or the largest possible, Mr. Thomas is mistaken in terming this a "relatively small earthquake-generated tsunami...". An ~8.9 magnitude quake is still larger than a vast majority of seismic events that occur or ever have occurred. I believe Mr. Thomas might agree with my qualification, so I will note that his relative scale seems to be derived from a misunderstanding of "superfaults". He says:

'...geologists are now talking about metamorphosed rocks bordering ancient fault lines that were caused by "megaquakes" that left behind "superfaults." The superfaults caused so much friction that they melted the rock on either side of the faults, where the rocks rubbed together. Today's earthquake...are not nearly this powerful.' (emphasis added)

Superfaults acquire their name from the exceptionally large displacement that takes place (i.e. where the fault blocks have moved several tens of meters relative to each other), typically as a result of landslide or meteor impact. They are not simply bigger versions, therefore, of earthquakes seen off the coast of Japan, Chile, Alaska, or New Zealand. Superfaults are most commonly associated with caldera collapse, where the emptied magma chamber of a volcano caves in, or meteor impacts, which cause significant displacement for more obvious reasons.

Secondly, the presence of melted rock "on either side of the faults" is not unique to "superfaults", but is found in nearly every fault that cuts through solid rock. Pseudotachylite is the proper term for a rock that has been melted along a fault trace from frictional heating [Note: Not all pseudotachylites are formed by frictional melting, but the term still applies to certain rocks that are]. Other evidences of frictional melting can range in magnitude from a semi-polished slickenside to a meters-thick layer of glass produced along faults near an impact structure.

The amount of fault offset produced by modern earthquakes depends on the cumulative strain (how much energy has been stored), but the movement occurs rapidly enough in all cases that frictional melting can also occur. As with the taffy analogy, rocks in the shallow (i.e. cold) part of the fault are typically too brittle for frictional melting to occur. Instead the rocks break apart to form fault gouge and breccia. But at depth, modern quakes are sufficiently powerful to melt rocks adjacent to the fault. Mr. Thomas is simply mistaken on this point.

The Noachian connection: is the extrapolation justified?

Earthquakes that occur beneath a large body of water (like the ocean) generate fast and energetic waves, which radiate toward coastlines. Since wave energy dissipates during the journey, tsunamis lose their destructive power with increasing distance to the coast. Have you ever wondered, though, why tsunami waves only become destructively significant at the coastal margin? Tsunami waves flood the shoreline because as the ocean water shallows, the wave has no choice but to 'topple over on itself'. If the water does not rapidly become shallow, the tsunami loses its power to 'stir things up' on land. In Mr. Thomas's picture of the Noachian flood, the continents would have already been covered with water (granted, not necessarily at a stand still). What kind of damage does he expect tsunamis to have incurred?

Furthermore, tsunamis come with little warning to the local population, even with seismic stations on constant watch. For many Japanese residents, tragically, one hour's notice was not sufficient to clear the coastline and escape the waves. But in Noah's day, the warning would have been about 59 minutes and 30 seconds less. If Mr. Thomas wants to consider tsunamis produced by the "breakup" of the "fountains of the deep" when interpreting the rock record, he should take into account this observation. Any tsunamis in Noah's day would have been capable of burying artifacts and lifeforms in place, yet no higher animals—including humans—or artifacts—buildings, tools, boats, etc.—are found in a majority of the rock record, if at all. Did life not exist near coastal margins, where it flourishes today? Mr. Thomas's understanding of the Flood is potentially predictive here, but fails to meet that test in the field.

Tsunamis had little effect on the rock record

As long as earthquakes occur at coastal or oceanic plate margins, tsunamis will be a part of Earth's everyday life, so to speak. While tsunami deposits have been found in the rock record (such as those associated with the Chicxulub impact), they are extremely rare. The reason is that more common geological processes (e.g. daily wave action, shifting river channels) are sufficient to rework tsunami deposits before they can be preserved, in most cases.

Mr. Thomas's understanding of the Flood is not corroborated by evidence in nature, even considering the destructive power of water stirred by earthquakes. Moreover, and as Mr. Thomas points out, the evidence of past earthquakes is now preserved along "fossilized faults". But these faults, including pseudotachylites of melt origin, occur in rocks that were supposedly deposited during the flood. How did this happen? For these faults to be preserved—and especially for faults to generate frictional heat and melt the rocks—the sediments must have been lithified (i.e. not unconsolidated, water-saturated grains) and under relatively high pressure and temperature. In attempting to solve one challenge to the Flood model (the origin of wave energy), Mr. Thomas actually raises bigger challenges to that model. The respective solutions, however, are mutually exclusive, and falsify the Flood model as a whole.

Sunday, March 27, 2011

Ken Ham and the Homeschoolers: the moral of the story is?

Relevant to all, as I see it.

Recently, Answers in Genesis president Ken Ham was barred from speaking at all upcoming homeschool conventions organized by Great Homeschool Conventions, Inc. (GHC). The latter is an effort to connect homeschoolers across the country with access to the newest curriculums, guest speakers, and simply a chance to interact with like-minded educators and students. GHC founders Brennan and Mary Jo Dean "believe in the God-given right and responsibility of parents to train and educate their children," and state explicitly—and unashamedly—that the purpose behind their conventions "is to honor the Lord Jesus Christ while facilitating events that are well-attended and professionally-produced, that well-serve Homeschooling families by providing ideas, information, instruction and encouragement that is relevant to homeschooling..." (read more here). In a position statement defending their decision (PDF available here), Mr. and Mrs. Dean also identify themselves with the young-Earth position promoted by Ken Ham and Answers in Genesis.

So what is the cause for division between these like-minded entrepreneurs in Christian education? Well, Mr. Ham was not the only speaker scheduled to speak at this year's Spring conventions. Dr. Peter Enns—Harvard graduate, former professor of Old Testament at Westminster Theological Seminary, and team member of Biologos—was also scheduled to speak, as well as promote his new Bible-study curriculum for homeschoolers.

In case you are neither familiar with Dr. Enns nor Biologos, I will simply point out that Dr. Enns does not share Ken Ham's view of the Genesis narrative. He has commented at length on the apparent exegetical problems that arise with reading Genesis similar to contemporary cosmologies and literature of the ancient Near East (i.e. as neither a critical history nor a complete metaphor, but a complicated narrative using both symbols and historical referents). With regard to the YEC position, he argues that one can not satisfactorily ignore the scientific evidence against a young-Earth reading—or abandon scientific method to make the position appear concordant with nature. Rather the answer to a meaningful synthesis lies within honest dialogue between Christians "that is both desperately needed and, in this modern age of science, inevitable." This conversation involves raising hard questions and challenging traditions that were born in a time when such questions would make little sense. [Further discussion, as well as exegetical challenges to the young-Earth position, can be found in Dr. Enns' response to Dr. Al Mohler, Jr. here.]

As you can imagine, Ken Ham was not silent about sharing the stage with the kind of person about which his ministry has tried to warn the Christian community. Prior to the scheduled conventions, Mr. Ham criticized both Dr. Enns for his position on scripture and Great Homeschool Conventions for letting Dr. Enns and others like him inside.

And by 'others', I mean vendors soliciting homeschoolers with science curriculums that teach Earth history prior to 4,004 B.C.

Both Ken Ham and Peter Enns have published in books, articles, and personal blogs that criticize the other's position on Genesis, science, scripture, etc. So why was Ken Ham uninvited, while the counter-perspective was unintentionally promoted and GHC's reputation put at risk? In the words of Mr. and Mrs. Dean, "Dr. Ham was removed for his spirit not for his message." If you're not sure what that means, compare the following excerpts from the respective speakers:

"Although I disagree with a literal reading of Genesis 1, I have no personal qualms with those who think differently; indeed there are a number of variant readings I am fine with..." (emphasis added)

"I realize you [Dr. Mohler] may disagree here, and maybe you have a way of seeing literal days where there is no sun [Gen. 1:1-13]. I disagree strongly but that would not lead me to question your commitment to the Gospel." (emphasis added)

Dr. Peter Enns to Dr. Albert Mohler, Jr. —Posted at Biologos here, July 28, 2010

"For instance...there are a number of people [at the convention] (including speakers) that are associated with the extremely liberal Biologos Foundation—an organization that is dedicated to trying to get people in the church to believe evolution and millions of years as fact." (emphasis added)

"But at the same time, I praise God for the opportunity, that even in this sea of lies permeating our culture, I am able to teach the truth of God’s Word to many." (emphasis added)

Posted on Ken Ham's blog, March 19, 2011

Mr. Ham's comments would not come as a surprising to anyone familiar with his work, but few that look up to him would think to check out his claims. First, Mr. Ham's identification of Biologos as a "liberal" institution is equivocal, because the grounds on which he defines it as such are unstated/unproved, and seem rather to work connotatively in his favor toward an audience that identifies liberalism with 'people that hate Christians'. This is called 'poisoning the well' by logicians.

Secondly, Mr. Ham makes it appear that Biologos was built on the motive to persuade Christians not to question Darwinism (or persuade them of any particular facts about nature, for that matter). Rather, their mission is to promote open and honest discussion among Christians concerning the harmony of science and faith without compromising either. This subtle accusation constitutes a caricature of Biologos on the part of Ken Ham.

Furthermore, Mr. Ham does not end his comments with repeated sentiments of disagreement contra the scientific norm. He continued with personal attacks upon Dr. Enns—labelled a "compromiser" by Ham—, in which he misrepresented the motives and questioned the integrity of the former Westminster professor:

"What [Peter Enns] teaches about Genesis is not just compromising Genesis with evolution, it is outright liberal theology that totally undermines the authority of the Word of God...He does not have the same view of inspiration as I do. In fact, he doesn’t have the biblical view of inspiration: 'All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness,'  (2 Timothy 3:16)." (emphasis added)

Again, use of the term "liberal" is vague, and deters the inquisitive reader from following up on the claims since the reputation of the accused is already tainted (i.e. another example of 'poisoning the well' by Mr. Ham). On the contrary, while Dr. Enns does not fall completely in line with the 'traditional view' of Biblical inerrancy, his view of Scripture by no means undermines the divine authority thereof. Moreover, simply quoting scripture does not constitute an argument, but invites readers to think Dr. Enns feels free to dismiss parts of scripture at will. Since this is not the case, Mr. Ham's accusations are dishonest. Dr. Enns, like many others—and I would argue, even young-Earth proponents—has simply made the case that God has spoken through men and women of old without 'correcting' their mistaken (but not stupid or ignorant) scientific views of the world.

This might cause discomfort to some young-Earth Creationists, but I believe it actually reveals the beauty of God's revelation. If the Genesis narrative were written in a way that was scientifically concordant, we might ask, "concordant to which science?" Those that work in scientific fields understand 'science' as dynamic, thus any attempt at scientific concordance within the inspired text would leave centuries of readers clueless as to the real meaning and render the narrative obsolete after a certain point. Yet God spoke in such a way that readers from all generations could understand the simple message and be drawn to the Gospel: the creator God, who brings light and life out of darkness, has made a covenant with man, through which He will be shown faithful in the end, though man sought to be a law unto himself and despised the blessings of the covenant.

Mr. Ham later attempted to justify his comments through the following analogy:

"If I saw a child playing with something harmful (e.g., poison), but thought it would be unloving to stop the child from doing this and warn them, I would not be doing what a concerned Christian should...There are many dangers within the church, including those created by Christian leaders who detrimentally affect our children and their faith in the Lord and His Word. It would be very unloving of me not to warn parents about this situation."

I would guess that now Mr. Ham understands how many Christians feel about his own teaching children that humans and dinosaurs coexisted, fossils were formed ~5,000 years ago in a worldwide catastrophe, the Earth's glaciers accumulated and receded within half a millenium, tectonic plates moved hundreds of miles in several months, mountain ranges—including the Himalayas, Andes, Rockies, Alps, etc.—were formed during such tectonic rearrangement, all living species today are descended from the survivors of the Flood, most species developed through evolutionary processes (speciation) while repopulating niches left vacant by said Flood (because they couldn't have all fit on the Ark), and that radioactive decay rates accelerated by nearly 1-million fold in the past just because...otherwise we couldn't explain radiometric dating. But as Dr. Russell Humphreys has noted, this accelerated decay had no serious impact on Noah's health (and those aboard the Ark) because otherwise we wouldn't be here to discuss it.

My intention is not to mock Mr. Ham, whom I believe to be sincere in his defense of what he perceives to be God's message. Rather, I am pointing out that certain members of the Christian community (myself included) view Mr. Ham's approach to the Bible and Earth history as potentially dangerous to "our children and their faith in the Lord and His Word", because those children will at some point have to reconcile the fact that the creation does not corroborate a young-Earth position. Since we believe this constitutes an unnecessary stumbling block to Christians, we also find ourselves compelled to warn others about the situation. But unless we speak with love, respect, and understanding—and with willingness to engage the counter-perspective in honest dialogue—our respective warnings will fall on deaf ears, and rightly so.

In the end, Mr. and Mrs. Dean are vindicated by their own, most brilliantly constructed words, found near the end of their position statement:

"We believe Christian scholars should be heard without the fear of ostracism or ad hominem attacks. Furthermore, a well-rounded education is not possible without knowing and understanding all sides of an issue. Such a process will, understandably, confirm one in their conviction or persuade them to make a change. But, again, that is the nature of debate and education." (emphasis added)

I applaud Mr. and Mrs. Dean for their integrity in such a bold move. I say this not because I disagree with Ken Ham on this issue, or agree with Peter Enns, for that matter—my heart is wholly bound to neither. Whatever your own position may be on the Bible, creation, or even homeschooling, I believe Mr. and Mrs. Dean deserve recognition for elucidating the very heart of education, which requires, at times, uncomfortable confrontation with those who may challenge your own convictions. After reading the position statement, I am not at all surprised that homeschooling produces some of the more active and profound thinkers in our society.

And so the moral of the story is?

In my opinion, the greatest obstacle to uncovering truth is our own pride. No matter how strong our convictions, if we would seek to silence the 'opposition' through censorship, then our unstable foundation will become evident, and earnest seekers of truth will take notice. At this point, it matters not whether Mr. Ham's position is correct. In preventing open dialogue and attacking the man rather than the argument, his own words have been rendered ineffectual.

Is there anyone that cannot relate to this example on some level?

Saturday, March 19, 2011

Cross bedding in beach sediments—then and now

I am always fascinated by pictures of the past that are engraved in rocks.

Whether it is an ancient inscription, a fossil, or even a tombstone, rocks are nature's photo album. As such, they can provide a faithful and direct link to some rather eerie moments in Earth history: a battle report, a last breath, a last word. Although we are oft at the mercy of geologic processes with regard to the "photo's" content, timing, and preservation (most are destroyed), each picture offers an invaluable resource in our futile—but well-intentioned and captivating—attempt to reconstruct a 4.5 billion-year tale.

Last week, I came across one such inscription. On a moderately populated beach in Santa Barbara, California, recent beach deposits have been preserved through a peculiar substitute for cementation: the tarry remnants of seeping oil. The photo on the right captures a mound of beach sand that has been cut by wave erosion and now stands above high tide. The grain composition is dominantly quartz, with a minor abundance of mica, so the sedimentary unit's dark color results from viscous oil that has found its way through the pore spaces to the surface.

Natural asphalt

The source of the oil is diatomaceous marl of the Miocene Monterey Formation, which was deposited between 17.5 and 6 million years ago. Such rocks form as a mixture of clay particles and diatom frustules accumulates in deep marine settings (typically at 200–2000 meters depth). Organic material—mostly the remains of surface-water algae and bottom-dwelling bacteria—is captured by adsorption onto the clay particles. Since the water was oxygen-depleted at depth, sufficient organic matter was preserved to make the sediments 'oil-prone'. More recently in Earth history, the sediments were buried deeply enough that ambient temperatures promoted the conversion of solid, residual organic matter (kerogen) to liquid hydrocarbons (bitumen, or what is commonly known as oil).

Because oil is less dense than water, which saturates porous rocks in the subsurface, buoyant force causes it to migrate toward the surface unless trapped by an impermeable barrier. The migration of oil is by no means a rapid process, taking years to thousands of years to move only a few meters (e.g. Bekele et al., 2002). In southern California, the oil is particularly viscous, thus natural oil seeps exist along the beaches of Santa Barbara even today.

"This far you may come and no farther; here is where your proud waves halt"

The most obvious characteristic of the sand pictured above is the prominent bedding (seen now as a linear pattern on the surface). Most of the bedding is planar (near horizontal), but a ~20 cm-thick bed of cross-bedded sand is evident near the middle of the photo. Planar bedding develops as wave after wave of ocean water distributes river-derived sand grains across the beach (aggradational stacking). Epsilon cross bedding (angled bedding with a 'curve' to it) and low-angle cross-stratification develop as channels and dunes migrate across the beach surface (progradational stacking). Both processes are typical in a nearshore environment, and so both features are diagnostic of nearshore environments in the rock record.

A link to the past

I imagine that many thousands of people have passed the outcrop above, but relatively few have considered its significance in historical geology. The bedding patterns stuck out to me in particular because I had seen them before. This was the first time, however, that I had witnessed such sedimentary structures forming in their 'native' environment. Below is a picture from my field experience in western Utah a couple years ago. Before I divulge any details, consider the similarities and differences between the outcrop in (A) Utah and (B) California.

First, the outcrop in Utah is well cemented (indurated) and appears as 'solid rock', whereas the beach outcrop is unconsolidated sand, only held in place by tar. Second—and not apparent from the photo—the rocks from Utah are comprised of carbonate (calcite) sand rather than quartz. Carbonate sand is more common in tropical, passive margin settings (like Florida, or the Bahamas). Related to this difference is the presence of coarse (pebble/cobble) clasts in (B), which is merely a function of the tectonic setting. The California coast is an active tectonic margin, in which river channels carry large clasts from mountainous terrane near the coast. Furthermore, California waves are currently forming an angular unconformity, since near-vertical rocks outcrop along much of the coast. The weathered remnants of those rocks are commonly preserved within the settling sand.

Despite these several differences between each outcrop, the genetic relationship is obvious. Sedimentary structures within both are most parsimoniously interpreted as having resulted from aggradational and progradational stacking of sand-sized sediments in a nearshore environment. In other words, both outcrops are perfect snapshots of historical beaches in the respective regions.

Deep time

The phrase "deep time" refers to the concept within geology that Earth history is incomprehensibly longer than human history. I would suggest, however, that when properly understood, the rock record is an effective tool in bringing this concept down to our level, just as a telescope peering into space captures comparably distant moments in the life of ours and other galaxies.

To wrap up the analogy I've set forth, consider that the rocks in Utah (outcrop A above) are part of the Cambrian Orr Formation, which was deposited some 500–493 million years ago. At that time, western Utah and Nevada actually marked the northern coast of what is now North America (that is to say, the continent has since rotated ~90° counter-clockwise). The region was also situated in the tropical zone, very near the equator, along a slowly subsiding passive margin, like the modern-day East Coast. Together, these facts account for the compositional differences between the outcrops noted above. But when set side by side with a recently formed analog, the time gap effectively vanishes.

And such is the allure of geology.


Bekele, E.B., Person, M.A., Rostron, B.J., Barnes, R., 2002, Modeling secondary oil migration with core-scale data: Viking Formation, Alberta basin: American Association of Petroleum Geologists Bulletin, v. 86, p. 55–74.

Tuesday, March 15, 2011

Idle times?

I thought it worth mentioning that midterm exams/projects, as well as a four-day field trip, tend to reduce my proficiency here.

But on the bright side, I learned plenty about California geology. Perhaps I could incorporate it here?

Wednesday, March 2, 2011

Inventing the isochron: Steve Austin, Andrew Snelling, and the Cardenas Basalts of the Grand Canyon

At the beginning of the year, I reviewed an article that cited anomalously old radiometric dates for historical lava flows to argue against the validity of the Potassium-Argon (K-Ar) dating method. Therein, I proposed that young-Earth authors ubiquitously employ the following approach in their discussions of radiometric dating:

1) Remind readers that several assumptions are inherent to radiometric dating methods.
2) Provide a case-in-point where at least one of those assumptions was falsified.
3) Extrapolate the proven uncertainty to the rest of geochronology without qualification.

Earlier this month, Answers in Genesis (AiG) reposted a study by Dr. Steve Austin and Dr. Andrew Snelling, entitled “Discordant Potassium-Argon Model and Isochron “Ages” for Cardenas Basalt (Middle Proterozoic) and Associated Diabase of Eastern Grand Canyon, Arizona”. The study was originally published in 1998, but one may assume from the recent posting that the authors consider the information sufficiently up-to-date. With that being said, I believe this article provides good opportunity to 1) test my proposal regarding the young-Earth approach, 2) discuss the validity of the K-Ar dating method, and 3) determine whether the young-Earth geologists offer a valid explanation for the results of radiometric dating.

How old are the Cardenas Basalts?

More than a mile of sedimentary rock is present below the Phanerozoic (less than 542 m.y. old) strata of the Grand Canyon—the latter characterized by their near-horizontal, “pancake-layer” stratigraphy. The Precambrian-age sediments were deposited, tilted, and subsequently eroded to form the Great Unconformity. The Cardenas Basalt unit is actually comprised of several lava flows, which overly the Dox Formation and cap the Unkar Group as a whole. Overlying the weathered surface of the Cardenas Basalt is the Nankoweap Formation—a coarse-grained sandstone unit. For those interested in detailing the Precambrian history of the Grand Canyon, the date of the Cardenas Basalt lava flows is of upmost importance, because it provides a minimum age for the rocks below and a maximum age for the rocks above. McKee and Noble (1976) reported a Rb-Sr isochron age for the lava flows of 1090±70 Ma, which was later refined by Larson et al. (1994) to 1103±66 Ma. The latter date has been used by subsequent researchers as the most accurate age of the formation.

Also preserved within Precambrian sediments are mafic dikes and sills, which cut through the Unkar Group. Elston and McKee (1982) provided a Rb-Sr isochron age of 1070±30 Ma for the mafic dikes/sills, which is concordant with the isochron age for the Cardenas Basalts. Although no field evidence is available for a genetic relationship between the intrusive rocks (dikes/sills) and the Cardenas Basalts, the similar age (Elston and McKee, 1982; Timmons et al., 2001) and mineralogical composition (Hendricks and Lucchitta, 1974) corroborate that possibility.

Discordant radiometric dates using the Potassium-Argon (K-Ar) method

A few years after the initial Rb-Sr age was published, Elston and McKee (1982) provided whole-rock and mineral K-Ar ages for the Cardenas lava flows and associated dikes. Their analysis yielded a range of ages (790–958 Ma), which were significantly younger than the 1090 Ma age published by McKee and Noble (1976). The result is not entirely unexpected, however, because the K-Ar method assumes perfect retention of argon—a noble gas—since the minerals cooled below the blocking temperature. This condition is not always met, as subsequent geological disturbances, such as heating events or deep burial, can easily promote the loss of argon and cause the samples to appear younger. Elston and McKee (1982) interpreted the ages to reflect partial loss of argon during subsequent rifting in the Neoproterozoic, when temperatures climbed in the deeply buried lava flows and dikes.

Larson et al. (1994) complemented the work of Elston and McKee (1982) with two new K-Ar ages from low-K samples (1.2–1.3 wt% K2O). The apparent ages of 957 Ma and 1013 Ma are significantly closer to the crystallization age of the basalts (1090 Ma), and caused Larson et al. (1994) to consider the relationship between potassium concentration and apparent K-Ar age. An inverse exponential relationship between weight percent K2O and K-Ar age was consistent with the hypothesis that burial alteration caused higher argon-loss in the more felsic, potassium-rich samples, which contained more glassy groundmass. Moreover, their results were consistent with Elston and McKee’s (1982) hypothesis that a Neoproterozoic heating event caused the partial loss of argon, and thus a partial resetting of K-Ar clocks.

Below is a plot of K-Ar ages of the Cardenas Basalts against K-content, including new data from Austin and Snelling (1998). With the exception of three outliers (in green), the logarithmic relationship explains most of the variance, reflecting the fact that K-rich rocks are more susceptible to alteration that undermines the retentivity of argon. The relationship is not perfect, however, because the rocks are spread over a wide geographic region and stratigraphic position, and may have undergone varying degrees of alteration to begin with.

Relevant studies since the publication of Austin and Snelling (1998)

Dating of the Cardenas Basalt and related magmatic events is not only important to stratigraphers. Paleogeographers also use the magnetic signatures of these rocks (along with their ages) to plot the movement of the continents throughout time. Timmons et al. (2001) provided 40Ar/39Ar dates for the mafic dikes and Cardenas Basalts. Interpreted age spectra range from 771–988 Ma, suggesting non-uniform loss of Ar during burial (2–3 km depth) and heating (<250°C) as a result of rifting between 800–742 Ma. Individual steps during 40Ar/39Ar analysis indicate one of the dikes is at least 1050 Ma, however, consistent with the Rb-Sr isochron ages reported earlier. Weil et al. (2003) reported 40Ar/39Ar dates from individual biotite minerals in two mafic dikes. The analysis revealed the presence of excess argon in the initial steps, but the authors interpreted an age of 1090.6±4.5 Ma from the concordant, higher temperature steps. Finally, Timmons et al. (2005) reported a 40Ar/39Ar age of 1104±2 Ma for an individual biotite within a mafic sill (most precise age yet for the intrusive rocks associated with the Cardenas Basalts), along with U/Pb and 40Ar/39Ar ages (1120–1270 Ma) for detrital muscovite and zircons within the underlying Dox Formation.

Overall, the range of K-Ar and 40Ar/39Ar ages accurately reflects the geologic history of Precambrian strata in the Grand Canyon. While their discordance presents a challenge to researchers in the field, adequate familiarity with the assumptions and limits of the K-Ar and 40Ar/39Ar dating methods allows one to interpret the dates consistently within the conventional framework.

K-Ar isochron of Austin and Snelling (1998)

If you are not already familiar with the use of isochron dating, it may be helpful to review the process (Chris Stassen provided a technical, but well illustrated, explanation here). The isochron method is applicable to cogenetic (i.e. sourced from the same magma) igneous rocks, in which the initial concentration of radioactive parent element (40K) varied between samples, but the ratio of radiogenic daughter element (40Ar) to its stable isotope (36Ar) did not. If the assumptions of the method are met, one can determine the age of the sample as well as the initial concentration of radiogenic daughter (40Ar). In other words, the isochron method does not need to assume that no radiogenic daughter was initially present, and is superior to the traditional K-Ar method in this regard.

As mentioned, loss of argon subsequent to crystallization causes samples to appear younger when dated by the K-Ar method. If the loss of argon was consistent between samples (for example, if all samples lost all their argon), a K-Ar isochron can be used to infer when argon was lost, because such an event would effectively reset the isochron age. If the former hypothesis holds—that Neoproterozoic rifting caused argon loss as a result of heating—a K-Ar isochron should reveal an age near 800–742 Ma (coincident with rifting; Timmons et al., 2001).

Sample quality

To Austin and Snellings’ (1998) own admission, most of the rock samples are highly altered. Moreover, several of the samples (especially those high in potassium) contain abundant glass. When volcanic glass is altered, its ability to retain argon (an assumption of the K-Ar method) is significantly lowered. Faure and Mensing (2005, p. 121) put it this way:

“Samples that have been altered or that contain devitrified glass...and xenoliths or xenocrysts should be avoided...the Ar retentivity of devitrified or hydrated glass is questionable.”

From the outset, there is no reason to expect that the whole-rock samples of Austin and Snelling (1998) met the conditions assumed by the K-Ar method. If anything, they should be analyzing mineral isochrons, where some quality control is practical. Instead, we must expect that altered volcanic glass sufficiently retained the argon over time. If it did not, however, we might expect to see significant scatter in the isochron plots. In fact, that is exactly what we find.

K-Ar isochron for Cardenas Basalt samples

Austin and Snelling (1998) combined published K-Ar dates along with thirteen K-Ar dates from their own samples (submitted to various laboratories), and reported the data in Table 1 of their paper. Figure 5 contains their results plotted as a K-Ar isochron. Along with their new data, they plotted a “reference isochron” of 1100 Ma to emphasize strong discordance between the two, before any discussion of the physical reasons behind the discrepancy. Unfortunately, most of their readers are likely to have lost interest by this point, and might conclude that the study offers evidence against the conventional interpretation (or that accelerated nuclear decay offers a valid explanation).

To evaluate the claims of Austin and Snelling, it is helpful to analyze their data in steps. [Note: a least-squares regression is used for simplicity and lack of variance data, but illustrates the points sufficiently well.] Below is a K-Ar isochron using only data published prior to Austin and Snelling (1998; listed there in Table 1). Treating sample LPM:4E as a statistical outlier, the good fit (R2 = 0.998), intercept (698.11), and estimated age (781 Ma) are all consistent with systematic loss of argon, or equilibration of argon isotopes in an aged system, around the onset of Neoproterozoic rifting.

When new data from Austin and Snelling (1998) are plotted, the result is a poorly fitting isochron (R2 = 0.902) with a much younger age (554 Ma), and much higher intercept (1904). Moreover, the slope is heavily influenced by samples A:C-16 and A:C-19, which are extremely rich in potassium and altered volcanic glass (i.e. they have a low retentivity of argon, represent highly fractionated end-members, and may have been enriched in potassium during alteration). Excluding both samples from the isochron results in a greater age (873 Ma), but poorer correlation (0.84) and unrealistic intercept (-1049). In both cases, there is good reason to believe these samples did not meet the physical requirements of an isochron, which assumes: 1) equal values of 40Ar/36Ar at t = 0; 2) similar magma source; and 3) systematic loss of argon between all samples, if such occurred.

When all data are combined, the resulting “isochron” age of the Cardenas Basalt unit is 657 Ma (below), but with a relatively poor fit to the data (R2 = 0.895). Austin and Snelling (1998) use a weighted regression to calculate an age of 756 Ma (see Fig. 5, Austin and Snelling, 1998), but the poor fit of the linear equation is apparent from their plot as well. If taken as a meaningful indicator of age, the plot suggests that excess argon (40Ar/36Ar = 787) was present at crystallization, or that isotopic equilibration took place some time after (as a result of heating/alteration). But there is more to the story.

For a K-Ar isochron, 40Aro is the initial daughter (Do), and while the method does not assume a zero initial concentration, any enrichment must have been uniform throughout the samples. In their discussion on the application of isochrons, Faure and Mensing (2005, p. 59) note “experience indicates that, in some cases, lava flows erupted by the same volcano in a short interval of time have different values of Do.” Lava flows that now comprise the Cardenas Basalts vary widely in their chemistry and mineralogy, and reflect varying degrees of crustal assimilation (Larson et al., 1994). If excess argon was a factor (both isochrons—as well as data from Weil et al., 2003—suggest that it was), it is highly unlikely the enrichment was uniform between flows, and hence very likely that the isochron has no “age” significance.

Although there is good statistical and geological basis to reject the isochron as having little to do with crystallization age (or even an argon-resetting age), the new data add nothing to the geochronological discussion of the Cardenas Basalts. The reason is that the isochron, if real, indicates that argon loss took place near 756 Ma, similar to the hypothesized age of alteration (see above; Timmons et al., 2001).

On the other hand, if one assumes my interpretation that sample LPM:4E is a statistical outlier, and that samples A:C-16 and A:C-19 should not be included in the calculation (high-K, high glass, highly altered), the resulting isochron is highly concordant. A least-squares regression line (see below) yields an R2 value of 0.985 and an intercept of 308.7 (very near atmospheric value of 295.5). If the physical conditions were met, the plot suggest a complete loss of argon from the suite of rocks at 794 Ma—exactly when Neoproterozoic rifting was in full swing, the geothermal gradient was high (i.e. the rocks were reheated), and movement along the Butte fault promoted hydrothermal alteration of the glass-rich rocks, which undermined the argon retentivity of K-rich samples. This interpretation is not conclusive, being contingent upon field and petrographic inspections of the samples, but offers a valid explanation for the data of Austin and Snelling (1998) within a conventional geological framework.

Isochron age for Precambrian dikes and sills of the Grand Canyon

Austin and Snelling (1998) also constructed a K-Ar isochron using only the seven mafic dike/sill samples (although one sample, EM:(Tap), was excluded as an outlier), and calculated an age of 676±35 Ma, using a weighted regression line. Visual inspection of their plot (Fig. 6 in Austin and Snelling, 1998) reveals the poor fit of their isochron. For example, sample A:DI-10 appears as a complete outlier—the line is drawn outside of 2σ uncertainty for that point—even though it’s included within the age calculation! If A:DI-10 is treated as the only outlier, the resulting age (717 Ma) and intercept (257.9) are more reasonably within the confines of a meaningful isochron.

Despite the past discussion of argon loss during burial alteration and heating (especially around 800 Ma), the authors again plot a ‘reference isochron’ of 1100 Ma to show the ‘strong discordance’. For any geologist working in Precambrian geochronology of the Grand Canyon, these results would not be unexpected and, in fact, only corroborate previous hypotheses regarding the discordance. While the isochron age is broadly consistent with total loss of argon during a heating event ~800-742 m.y. ago, however, a few details should be considered.

Evolving magma chamber (source)
First, as the authors point out, the slope (and thus age) of the isochron is strongly determined by the high-potassium granophyre samples. The mineralogy and chemistry of the granophyre is due, however, to extensive fractional crystallization in the magma chamber, which may also have been accompanied by crustal assimilation (Larson et al., 1994). An isochron date, using the K-Ar method, assumes that each sample had an equal 40Ar/36Ar ratio at t = 0, but it is unlikely that this condition was met if crustal material was incorporated (the ratio is much higher in rocks surrounding the dikes/sills) or if the intrusive magma varied in viscosity and retentivity of argon during cooling. Excluding both granophyre samples from the isochron increases the estimated age to ~823 Ma, but with higher uncertainty.

Statistical significance of the isochron, and physical meaning of its intercept
The coefficient of determination (R2) for the isochron of Austin and Snelling (1998) is not reported, but appears to be less than desirable, as mentioned above. A least-squares regression line calculated from their reported data (treating A:DI-10 as an outlier) is 0.93, which, although high, is on the low end for most published isochrons. Moreover, R2 is highly affected by the granophyre samples, which, if excluded based on the discussion above, reduces the coefficient to 0.88. In other words, it is very likely that the isochron reflects neither a true crystallization age nor age of complete resetting.

Austin and Snelling (1998) reported the intercept of the isochron as 453, which would suggest the presence of excess argon during crystallization. Given the poor fit of the isochron, however, more likely scenarios are: 1) excess argon was present in each sample, but not to the same degree, or 2) argon was lost from each sample, but not to the same degree. One means to test this independently is through the use of 40Ar/39Ar dating, which can account for excess argon or reveal differential argon loss. Reported 40Ar/39Ar ages for the mafic dikes range from 771–988 Ma (Timmons et al., 2001) and age spectra are “highly disturbed”, corroborating the latter possibility.

Alternative explanations of Austin and Snelling

Once the geochronological data is properly evaluated, there is little room for discussion on ‘discordance’ of K-Ar isochrons. Nonetheless, the authors evaluated the possibility of argon resetting as the result of the young K-Ar isochron age. Strangely, they used a 516 Ma isochron age (Fig. 3, which is not really an isochron) as the “best” apparent age for the Cardenas Basalts, even though the plot contains several outliers (beyond 2σ from the regression line) that were included in the calculation. Also, the plot cannot account for extraneous argon. Without mention of the real isochron age suggested by their data, they argue as follows:

“...an age of 516±30 Ma is Upper Cambrian, not Proterozoic. The conventional interpretation of Grand Canyon Upper Cambrian stratigraphy at Basalt Canyon is that the Tapeats Sandstone (Upper Cambrian) was sitting level on the floor of an ocean just above the Great Unconformity and just a few hundred meters above 12° dipping Cardenas Basalt. No trace of the assumed Upper Cambrian heating event is seen in the Tapeats Sandstone at Basalt Canyon. Therefore, the reset model has incorrect timing and fails to explain the K-Ar data within conventional geology.”

Of course, such an age is not warranted by their data, so the argument is not worth considering. Austin and Snelling continue to describe argon leakage, inheritance, and mixing models—all of which are unnecessary explanations for data that don’t form an isochron!

Accelerated nuclear decay—steaks ‘well done’, anyone?

Not surprisingly, Austin and Snelling present at least one completely absurd scenario: that the rate of radioactive decay was significantly higher in the past, and more so for the Rb-Sr system than for K-Ar. They pose the following question:

“Could 87Rb decay and/or 40K decay constants be altered to make the data be interpreted in a concordant way? The mathematics simply requires a change to one or both decay constants and they could be concordant.”

And the answer is: no. The mathematical fix is not as simple as they propose and is falsified quickly when all data are considered. If we assume that Rb decayed at ~twice the rate of K (to force concordance on the 1103 Ma and 516 Ma isochron ages, respectively), then the 40Ar/39Ar biotite ages of 1102 Ma (Timmons et al., 2005) and 1090 Ma (Weil et al., 2003) are no longer concordant from any perspective. Furthermore, magmatic events around 1100 Ma occurred throughout the whole North American continent and have been dated concordantly by the K-Ar, Rb-Sr, and U-Pb methods (Larson et al., 1994; Timmons et al., 2005). These data simply make no sense if decay rates changed to different degrees at any point in Earth history.

Of course, the best reason to reject outright any notion of accelerated nuclear decay is the heat problem. In essence, radioactive decay releases heat, and proposing that ~1 billion years worth of decay occurred in a matter of years would cause significant problems for any living creatures in the universe at that time (the heat released would be enough to melt the Earth several times over). Young-Earth researchers are aware of this problem, but have offered no valid solution. For more information, Dr. Larry Vardiman of ICR summarizes the problem here, while the American Scientific Affiliation has provided several technical discussions here on their website.


Within their paper, Austin and Snelling (1998) remind their readers of the assumptions behind the K-Ar dating method (for example, that it “assumes no radiogenic 40Ar was present when diabase and lavas cooled to form rocks”). They proceed to demonstrate that K-Ar ages range over several hundred million years, and that “wide variation in model ages remains unexplained” (contrary to published literature elsewhere on the topic). Without any specific discussion of the meaning behind isochron ages—what it might represent or how one is recognized—they plot their results as evidence of discordance between the K-Ar and Rb-Sr isotope systems. For the uninformed reader, it may seem as though a rough, linear trend in data points constitutes a valid isochron.

Differential loss of argon during burial alteration, and even interaction with hydrothermal fluids during movement along the Butte fault, can account for the discrepancy in K-Ar dates, relatively poor statistical significance in the isochron, and disturbed 40Ar/39Ar age spectra. Thus Austin and Snellings’ new K-Ar data are not inconsistent with previous hypotheses regarding the geologic history of these rocks and their deviance from the accepted age of 1103 Ma. When the most potassium-rich samples (which contain abundant volcanic glass and plot as outliers) are removed from the calculation, the resulting isochron is statistically significant and suggests resetting of the argon system near 794 Ma—inline with the age of thermal disturbance to the region.

Even apart from the model above, there is good geological and statistical foundation on which to reject the isochron from Austin and Snelling (1998) as an indicator of the rocks’ age (crystallization or metamorphism). Coincident magmatic events are recorded on the North American continent, and date near 1100 Ma using several methods (Rb-Sr, U-Pb, and K-Ar). Furthermore, several good 40Ar/39Ar dates (with undisturbed age spectra) are available for the dikes/sills, and agree with the Rb-Sr isochron age of 1103 Ma (Weil et al., 2003; Timmons et al., 2005). For the argument of Austin and Snelling (1998) to have any relevance, they must be able to account for this data. Instead, they propose the unrealistic “model” of accelerated nuclear decay (i.e. change in decay rates) to account for the apparent discordance, despite the fact that it would contradict regional K-Ar and Rb-Sr data already available to them (e.g. Larson et al., 1994). Despite their in-depth, technical discussion of the isotope geochemistry and petrology of Grand Canyon samples, the conclusions of Austin and Snelling (1998) are the result of bad scientific practice and a propagandist effort to dissuade uninformed readers from lending any credibility to geochronology.

References Cited:
Austin, S.A., and Snelling, A.A., 1998, Discordant Potassium-Argon Model and Isochron “Ages” for Cardenas Basalt (Middle Proterozoic) and Associated Diabase of Eastern Grand Canyon, Arizona: Proceedings of the Fourth International Conference on Creationism, p. 35-51.

Elston, D.P., and McKee, E.H., 1982, Age and correlation of the late Proterozoic Grand Canyon disturbance, northern Arizona: Geological Society of America Bulletin, v. 93, p. 681-699.

Faure, G., and Mensing, T.M., 2005, Isotopes: Principles and Applications (Third Edition), Wiley, 897 p.

Hendricks, J.D., and Lucchitta, I., 1974, Upper Precambrian igneous rocks of the Grand Canyon, Arizona, in Karlstrom, T.N.V., Swann, G.A., and Eastwood, R.L., eds., Geology of northern Arizona, Part 1—Regional studies: Geological Society of America Field Guide, Rocky Mountain Section, p. 65–86.

Larson, E.E., Patterson, P.E., Mutschler, F.E., 1994, Lithology, chemistry, age, and origin of the Proterozoic Cardenas Basalt, Grand Canyon, Arizona: Precambrian Research, v. 65, p. 255–276.

McKee, E.H., and Noble, D.C., 1976, Age of the Cardenas Lavas, Grand Canyon, Arizona: Geological Society of America Bulletin, v. 87, p. 1188-1190.

Timmons, J.M., Karlstrom, K.E., Dehler, C.M., Geissman, J.W., Heizler, M.T., 2001, Proterozoic multistage (ca. 1.1 and 0.8 Ga) extension recorded in the Grand Canyon Supergroup and establishment of northwest- and north-trending tectonic grains in the southwestern United States: Geological Society of America Bulletin, v. 113, p. 163-181.

Timmons, J.M., Karlstrom, K.E., Heizler, M.T., Bowring, S.A., Gehrels, G.E., Crossey, L.J., 2005, Tectonic inferences from the ca. 1255–1100 Ma Unkar Group and Nankoweap Formation, Grand Canyon: Intracratonic deformation and basin formation during protracted Grenville orogenesis: Geological Society of America Bulletin: v. 117, p. 1573-1595.

Weil, A.B., Geissman, J.W., Heizler, M., Van der Voo, R., 2003, Paleomagnetism of Middle Proterozoic mafic intrusions and Upper Proterozoic (Nankoweap) red beds from the Lower Grand Canyon Supergroup, Arizona: Tectonophysics, v. 375, p. 199-220.