Category Archives: Geology

Timefulness: How thinking like a geologist can help save the world (review; long)

Timefulness: How thinking like a geologist can help save the world, Marcia Bjornerud, Princeton University Press, 2018/2020

There are many excellent overviews for the general reader of how life on Earth has changed over time (see, for a recent example, Neil Shubin’s Some Assembly Required, which I reviewed here recently. The history of the Earth itself has not been so well served, and Timefulness; How Thinking Like a Geologist Can Help Save the World, by Marcia Bjornerud, Professor of Geology and environmental Sciences at Lawrence University, is a welcome and timely addition to this badly under-represented genre. [1] The book is beautifully written, in plain language, with complex ideas explained with great simplicity and the use of strikingly appropriate verbal imagery. Behind this transparency of language lies a deep love and knowledge of her subject. The book should appeal to anyone looking for an overview of the Earth as the abode of life, or a perspective on our place in time, and how recklessly we are compressing the tempo of natural change.

The author presents her book as an argument for what she calls timefulness, the perception of ourselves as living in and constrained by time, of time itself as having both extension and texture, of the acceptance of our own mortality, and of our own responsibilities. This she sees as severely lacking in our society. We expect people to know something about distances on the map, but Read the rest of this entry

What does Mt St Helens teach us about Noah’s flood? Almost nothing.

CanyonGoogleEarthYoung Earth Creationists (YECs) argue from the rapid and dramatic events observed at the Mt St Helens 1980 eruption to the conclusion that the Earth’s geological record, as displayed for example at the Grand Canyon, could be the results of the even more dramatic events associated with a biblical worldwide flood. Geochristian, in the post I link to below, dismantles specific examples of this claim, and goes on to challenge the view that the Bible describes Noah’s Flood as a worldwide catastrophe anyway. Illustration: Step Canyon, Mt St Helens; Google Earth via Geochristian

Regarding geology, the YEC arguments derive their rhetorical power from the all-or-nothing thinking that runs through all their positions. They claim that Mt St Helens demonstrates the correctness of catastrophism over geological gradualism. If all this much can happen so quickly, why assume that the Earth’s deep geology really required deep time? If the flowing ash and mud from Mt St Helen’s shows lamination and cross bedding, does that not destroy the geologist’s argument that the lamination and cross bedding of shales and sandstones are the result of slow deposition? If in a matter of days snowmelt carved a canyon in the Mt St Helens deposits, would not the waters of a year-long flood have sufficed to carve out the Grand Canyon? If the Mt St Helens eruption rapidly uprooted and re-deposited large number of trees, could not the Earth’s fossil fuel deposits have been formed in the same manner?

Geochristian discusses each of these claims in detail (spoiler; none of them will stand up to examination). What I want to point out here is how much they all have in common. They all depend on imposing absolute either/or divisions on reality, cherry picking similarities and ignoring differences, and imposing the simplest of models on complex reality. The dispute between catastrophism and gradualism, although repeatedly revived by creationists (see e.g. here ) was pronounced dead by TH Huxley, “Darwin’s bulldog”,in his Presidential Address to the Geological Society in 1869 It’s simply a matter of perspective. Catastrophic events do happen from time to time, but not very often, giving the impression of gradualism over long periods of time. Cross bedding can occur catastrophically, in well-understood special circumstances, but geologists have never had any difficulty in distinguishing between what is found in sudden volcanic outpourings and the completely different wind-blown cross bedding observed in desert sandstones, including ironically the Coconino Sandstone within the Grand Canyon itself. Canyons such as Mt St Helens Step Canyon can indeed form very rapidly in uncompacted sediments, but the Step Canyon is straight, and carved on a steep slope through soft debris, while Grand Canyon has bends and is carved through extremely hard rock by a river flowing over a plateau with, overall, a gentle gradient. And the tree debris from Mt St Helens bears no resemblance, either in texture or in amount, to the world’s coal fields.

Next, Geochristian attacks the YEC interpretation of Genesis. In particular, the word “eretz”, describing the territory immersed in the flood, can mean either the Earth, or a more limited region. Here his motivation is to preserve faith in the text, while rebutting the interpretation that requires the flood to be worldwide. My own approach would be rather different. In the biblical narrative, God sets out to destroy mankind, apart from the virtuous relic represented by Noah and his family. This could hardly have been accomplished by a merely local flood, though one could well argue that the author(s) of Genesis did not make a clear mental distinction between local and worldwide. However, the entire problem disappears if you regard the Genesis narrative (or, rather, fused narratives) in context within a much more ancient Mesopotamian literature, and I argue that this is actually more respectful of the text than supernaturalist literalism. However, in my experience discussions between those who do, and those who do not accept a supernatural origin for Scripture are rarely productive.

So why I am I, an unbeliever, re-blogging Geochristian’s material at all? Because as I see it, the crucial gulf is not between religious believers and unbelievers, but between those who are willing to accept reality in all its complexity, and those who prefer to impose their own dogma. And this does not affect only such matters as evolution and the age of the Earth, but such intensely practical matters as conservation, global warming, the regulation of market-based economies, and, right now, our reaction to one particular virus that happens to have mutated and evolved.
h/t Michael Roberts





All I got from Mt St Helens (MSH) in the days following its May 18, 1980 eruption was a few pretty sunsets. I was an undergraduate student in my first year at the University of Utah, and most of the ash cloud passed far north of Salt Lake City. MSH became more significant for me a few years later as a geology graduate student at Washington State University, where my research project involved analysis and correlation of Cascade Range tephra (volcanic ash) layers buried at various levels in the Quaternary Palouse Loess of eastern Washington. Some of these tephra layers correlated to ancient eruptions of MSH, dated around 13,000 and 36,000 years ago.

Fortieth Anniversary

img571_900w_889h Credit: USGS, Robert Krimmel, public domain

Due in part to easy accessibility, the 1980 eruptions of MSH have been studied more closely than just about any other explosive volcanic eruption in history. Geologists have learned…

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Where rocks touch: geologic contacts

Another delightful posting from my friend Marli Miller.Thanks, Marli. I’ve blogged here earlier myself about the famous unconformity at Siccar Point, and the depositional contact at the Giants Causeway between a later lava flow, and the paleosol formed by weathering of the one before it.


Geologic contacts are the surfaces where two different rocks touch each other –where they make contact. And there are only three types: depositional, intrusive, or fault. Contacts are one of the basic concerns in field geology and in creating geologic maps –and geologic maps are critical to comprehending the geology of a given area. For those of you out there who already know this stuff, I’ll do my best to spice it up with some nice photos. For those of you who don’t? This post is for you!

Depositional contacts are those where a sedimentary or volcanic rock was deposited on an older rock (of any type). Intrusive contacts are those where igneous rocks intrude older rock (of any type). Fault contacts are… faults! –surfaces where two rocks of any type have moved into their current positions next to each other along a fault.

In a cross-sectional sketch they may…

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Shaping of Landscape: A primer on weathering and erosion

Landscape as process, beautifully illustrated. Students with Marli Miller as instructor are fortunate indeed


Most of us love landscapes –and many of us find ourselves wondering how they came to look the way they do. In most cases, landscapes take their shape through the combined processes of weathering and erosion. While weathering and erosion constitute entire fields of study unto themselves, this primer outlines some of the basics—which pretty much underlie all the further details of how natural processes shape landscapes.

Incised meanders on the Green River, Utah Aerial view of incised meanders of Green River, Utah.

Two definitions: weathering describes the in-place breakdown of rock material whereas erosion is the removal of that material. Basically, weathering turns solid rock into crud while erosion allows that crud to move away.

Weathering processes fall into two categories: physical and chemical.  Physical weathering consists of the actual breakage of rock; any process that promotes breakage, be it enlargement of cracks, splitting, spalling, or fracturing, is a type of physical weathering.  Common examples…

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Evolution of the River Nile

Reblogging from Steve Drury at wileyearthpages. In an earlier post (How to learn from creationists), I mentioned the case of the buried Nile canyon as one where I had learnt from answering creationists’ questions. This piece gives much more detailed interesting information, and I am surprised (not for the first time) to learn how young great river systems are in their present form.

The longest river in the world, the Nile has all sorts of riveting connotations in terms of archaeology, Africa’s colonial history, the romance of early exploration and is currently the focus of disputes about rights to its waters. The last stems from its vast potential for irrigation and for hydropower. It is probably the most complex of all the major rivers of our planet because it stretches across so many climatic zones, topographic systems geological and tectonic provinces. Mohamed Abdelsalam of Oklahoma State University, who was born in the Sudan and began his career at the confluence of the White and Blue Nile in its capital Khartoum, is an ideal person to produce a modern scientific summary of how the Nile has evolved. That is because he has studied some of the key elements of the geology through which the river and its major tributaries travel, but most of all…

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Grand Canyon Unconformities –and a Cambrian Island

I have discussed the Grand Canyon myself at , and strongly recommend this beautifully written and illustrated guide to its unconformities


A prominent ledge punctuates the landscape towards the bottom of the Grand Canyon. It’s the Tapeats Sandstone, deposited during the Cambrian Period about 520 million years ago, when the ocean was beginning to encroach on the North American continent, an event called the Cambrian Transgression. Above the ledge, you can see more than 3000 feet of near-horizontal sedimentary rocks, eroded into cliffs and slopes depending on their ability to withstand weathering and erosion. These rocks, deposited during the rest of the Paleozoic Era, are often used to demonstrate the vastness of geologic time–some 300 million years of it.

View of the Grand Canyon from the South Rim trail. Arrows point to the Cambrian Tapeats Sandstone. View of the Grand Canyon from the South Rim trail. Arrows point to the Tapeats Sandstone.

But the razor-thin surface between the Tapeats and the underlying Proterozoic-age rock reflects the passage of far more geologic time  –about 600 million years where the Tapeats sits on top the sedimentary rocks of the Grand…

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When dinosaurs roamed the Western Isles

Quite a challenge, I expect, to the local Free Presbyterians.

My friend Kim Johnson commented on the strange appearance of the footprints, Steve Drury (author of the blog of which this is just an annotated repost) referred me to Paige Depolo, senior author of the paper on which Steve’s post is based, and Paige replied as follows:

When it comes to the depositional environment, the tracks were formed in a low-energy lagoon and are generally preserved today as impressions into shaley limestone. Later, additional limestone layers were laid down at the site and in-filled the impressions. Those layers form the casts that we can still observe for some of the tracks today. In some cases at this site, the cast remains while the surrounding impression which it was originally infilling has been almost completely eroded. These rocks were deposited during the Middle Jurassic. Later, likely during the Paleogene, a sill was intruded immediately below the track bearing layer and the surrounding rocks were baked. The low-level contact metamorphism of the track-bearing layers definitely makes for some interesting looking exposures!

h/t Kim and Steve, and many thanks to Paige

Cuillin Hills, Isle of Skye, Scotland, UK Cuillin Hills, Isle of Skye, Scotland, UK (credit: Wikipedia)

The Isle of Skye off the northwest coast of Scotland  is known largely as a prime tourist destination, such as Dunvegan Castle with a real clan chief (The MacLeod of MacLeod) and its Faerie Flag; Britain’s only truly challenging mountains of the Black Cuillin; and, of course, the romantic connection with the Young Pretender, Charles Edward Stuart and his escape, in drag, from the clutches of the Duke ‘Butcher’ Cumberland, hence the Skye Boat Song. Geologists know it best for its flood basalts with classic stepped topography and the exhumed guts of a massive central volcano (the Cuillin), relics of the Palaeocene-Eocene (62 to 54 Ma) North Atlantic Large Igneous Province. The spectacular Loch Coruisk, a glacial corrie drowned by the sea, exposes the deepest part of the main magma chamber. It is also the lair of Scotland’s lesser…

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If you are interested in evolution, get this book

EVOLUTION: What the Fossils Say and why it Matters, Donald R. Prothero (2nd edition)

If you are interested in evolution, get this book. And make sure that your library gets it. And your children’s highschool library. Incidentally, it’s incredible value; list price $35.00/£27.95 from Columbia University Press, with over 400 lavishly illustrated pages.

The book is a comprehensive survey of the fossil record, supplemented at times with other evidence, and framed as one long argument against creationism. It opens with a general discussion of the ideas behind current evolutionary thinking, moves on to a survey of specific topics in (mainly animal) evolution, from the origins of life to the emergence of humanity, and concludes with a brief discussion of the threat that creationism poses to rational thinking. The argument is laid out clearly in the seemingly artless prose of an accomplished writer in love with his subject matter, with plain language explanations that presume no prior knowledge, while the detailed discussions of specific topics give enough detail to be of value, I would imagine, even to a professional in the field. The author is an experienced educator and researcher, with thirty books ranging from the highly technical to the popular, some 300 research papers, and numerous public appearances to his credit, and the work is copiously illustrated with photos, diagrams, and drawings by the author’s colleague, Carl Buell. These illustrations are an integral part of the work, graphically displaying the richness of the data at the heart of the argument. Read the rest of this entry

How to learn from creationists

“The wise learn from everyone.”1 The freak success (half a million reads) of my recent piece How to slam dunk creationists, and the subsequent discussion, have again set me thinking about how to learn from creationists. It is not enough to say, as Dawkins notoriously said, “[I]f you meet somebody who claims not to believe in evolution, that person is ignorant, stupid or insane (or wicked, but I’d rather not consider that).” Conversation is a two-way street, I have certainly learnt from creationists’ attacks on evolution, and if I am learning from them it is at least possible that they are learning from me.

Types of comment

Comments I have had from creationists fall into three broad groups (and note that contrary to what Dawkins says, some of these are at least partly informed, highly intelligent, and completely rational):

1) Simple misstatements

2) Appeal to the Bible

3) Purportedly scientific arguments, some without merit, while others refer to important issues.

From simple misstatements, not very much can be learnt, except perhaps the source of the misinformation. Remember that if someone quotes wrong information, the burden of proof is not on you but on them. Leave it there, as in this actual exchange: Read the rest of this entry

Volcanism and sea level fall

If there were decompression melting of magma in the West Antarctic volcanic province as the icesheet thinned, that would not be good news.

If the geological Society link in the article doesn’t work for you, try this one;

Most volcanic activity stems from the rise of hot, deep rock, usually within the mantle. Pressure suppresses partial melting, so as hot rock rises the greater the chance that it will begin to melt without any rise in its temperature. That is the reason why mantle plumes are associated with many volcanic centres within plates. Extension at oceanic ridges allows upper mantle to rise in linear belts below rift systems giving rise to shallow partial melting, mid-ocean ridge basalts and sea-floor spreading. These aren’t the only processes that can reduce pressure to induce such decompression melting; any means of uplift will do, provided the rate of uplift exceeds the rate of cooling at depth. As well as tectonic uplift and erosion, melting of thick ice sheets and major falls in sea level may result in unloading of the lithosphere.

During Messinian Stage of the late Miocene up to 3 km…

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