A snapshot in amber

A few days ago I finished reading the wonderful new book by paleontologist Riley Black, The Last Days of the Dinosaurs: An Asteroid, Extinction, and the Beginning of Our World.  I can't say enough positive things about it -- it tells the gripping story of the impact of the seven-kilometer-wide Chicxulub Meteorite, which hit a spot just north of the Yucatán Peninsula so hard that most of the giant rock vaporized, what was left punched twenty kilometers into the Earth's crust, and it left an impact crater 180 kilometers across.

Artist's impression of the moment of impact [Image is in the Public Domain courtesy of artist Donald E. Davis and NASA/JPL]

Black gives us a vivid description of the event and its aftermath, each chapter from the point of view of one individual animal who experienced it (not necessarily lived through it, of course).  The day before the impact; the impact itself; the first hour; the first day; the first year; and so on, up until a hundred thousand years after the strike, at which point the Earth's ecosystems had largely recovered -- albeit with a completely different assemblage of species than it had before.

Black's contention, which is generally accepted by researchers, is that there's little truth to the old trope of the dinosaurs being a moribund group anyhow and the asteroid just finished them off.  The dinosaurs were doing just fine.  While some species were headed toward extinction, that had been happening during the group's 190 million year hegemony (and has happened in every single group of life forms ever evolved).  Dinosaurs as a group were still widespread and diverse -- and if it hadn't been for the impact, it's pretty likely that they would have remained in charge (as it were) for millions of years afterward.

Which means that it's probable that mammals would never have taken off the way they did.  (More accurately, "the way we did.")  It's also an incorrect understanding that mammals only launched after the dinosaurs were "out of the way."  Mammals had been around for a very long time themselves (the first ones, the morganucodontids and multituberculates, overlapped the dinosaurs by over a hundred million years).  What seems to be true, though, is that the dinosaurs occupied most of the large-apex-predator and giant-herbivore niches, so mammal groups were mostly small, and a lot of them were burrowers -- something that was an adaptation to there being a lot of carnivores around, but turned into a key to their survival during the searing infrared surge that swept across the world the day the asteroid hit.

What brings this up, besides my wanting to promote Riley Black's awesome book, is a link sent to me by a friend and loyal reader of Skeptophilia about a series of recent discoveries by paleontologist Robert DePalma at a dig site in Tanis, North Dakota.  What's stunning about these finds is that DePalma believes -- and the evidence seems strong -- that they represent the remains of organisms that died on the day of the Chicxulub Impact.

In other words, we're looking at a snapshot of the event that killed every non-avian dinosaur species, and changed the face of the world permanently.

Hard as it is to imagine, in the late Cretaceous, what is now North Dakota was a tropical wetland bordering the Western Interior Seaway -- an inlet of the ocean that has since vanished from a combination of uplift, the Rocky Mountain Orogeny, and simple evaporation.  Picture southern Louisiana, and you have an idea of what North Dakota looked like.

Then the meteorite struck.

Despite the fact that the distance between the impact site and the Tanis wetland is around four thousand kilometers, it only took an hour before there was a blast of heat, a rain of red-hot debris, and a series of earthquakes.  The first-mentioned is probably what did the most immediate damage; large animals that were too big to shelter were probably all dead within minutes after the the infrared surge started, as were just about all the terrestrial plants.  Even aquatic organisms weren't safe, though.  One of the more horrifying fossil finds was a turtle -- that had a stick driven all the way through its body.  The earthquakes triggered a series of seiche waves, which occur when an enclosed body of water is shaken laterally.  (Picture the sloshing of water in a metal tub if you jostle it back and forth.)  The seiche in the Western Interior Seaway and nearby lakes flung aquatic animals onto shore and then buried them under tons of debris -- DePalma and his team found layers of fish fossils right at the K-T Boundary Layer that were also victims of that awful day the impact occurred.

I've written about this event before, of course; I've always had a fascination with things that are big and powerful and can kill you.  But what made me decide to revisit it was a new discovery at Tanis of amber that contains glass spherules.  Amber, you probably know, is fossilized tree sap; it can contain other fossils, including pollen and animals that were trapped in the sap before it hardened (made famous by Jurassic Park, although it must be added that there's never been any found with intact DNA).  But these glass spherules were altogether different.  Silicate rocks turn to glass when they're melted and then cooled quickly; that's where the rock obsidian comes from.  But an analysis of the spherules showed something fascinating.  There were inclusions in the glass of tiny chips of two different kinds of rock; one type was high in calcium, while the other was largely metallic, with high content of chromium, nickel, and other heavy elements.

The first, DePalma says, are the remnants of the limestone bedrock from the spot in the Yucatán where Chicxulub hit, blasted into the air and landing four thousand kilometers away.

The other are the (thus far) only actual pieces of the meteorite itself which have ever been found.

It's absolutely astonishing that we can identify rocks and fossils that formed on a specific day 66 million years ago, and doubly so that it was a day when an event occurred that quite literally changed the course of life on Earth.  As horrifying as the Chicxulub Impact was -- Riley Black calls it "the worst day the Earth ever experienced," and it seems an apt description -- in a real sense, we owe our existence to it.

Without Chicxulub, it's pretty likely it'd still be a dinosaur-dominated world -- and one in which mammals were still small, furtive furballs that never had a chance to control their own destiny.

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Double whammy

Having a rather morbid fascination with things that are big and scary and dangerous and can kill you, I've dealt more than once with topics like mass extinctions and asteroid collisions and supervolcanoes.  So naturally, when there was a piece of recent research on all three at the same time, I felt obliged to write a post about it.

The paper, published last week in Science, was written by a team of scientists from the University of California - Berkeley (Courtney J. Sprain, Paul R. Renne, Loÿc Vanderkluysen, Kanchan Pande, Stephen Self, and Tushar Mittal), is called "The Eruptive Tempo of Deccan Volcanism in Relation to the Cretaceous-Paleogene Boundary."  In it, they examine one of the biggest volcanic eruptions in Earth's history -- the Deccan Traps -- which seem to have occurred right around the time of the Cretaceous Extinction, 66 million years ago.

The Western Ghats, part of the Deccan Traps lava flow [Image licensed under the Creative Commons Nicholas (Nichalp), Western-Ghats-Matheran, CC BY-SA 2.5]

This certainly isn't a coincidence, and it's been thought for a while that the eruption, which occurred in what is now India and released an estimated one million cubic kilometers of lava, were at least contributory to the mass extinction that occurred at the end of the Cretaceous Period.  Such an unimaginably huge eruption would have burned everything in its path, converting any organic matter that got in the way into ash and carbon dioxide -- causing a spike in temperature that certainly would have put a huge strain on ecosystems to compensate.  The actual blow (literally) that marked the end of the Cretaceous Period, though, was an enormous meteorite collision, the Chicxulub Impact, near the Yucatan Peninsula on the other side of the planet.

Almost precisely on the other side, in fact.  This got Sprain et al. wondering if the two might be connected, especially since geologists still don't know what causes trap-type eruptions (there are two other trap eruptions known, the Emeishan Traps in China and the unimaginably huge Siberian Traps that are likely to be the cause of the largest mass extinction known, the Permian-Triassic Extinction).  Whatever the cause, it apparently happens without a great deal of warning, which is scarier than hell.  The crust of the Earth fissures, and phenomenal quantities of lava come pouring out, causing serious issues for anyone or anything living nearby.  But the observation that the Chicxulub Impact and the Deccan Traps are not only close to simultaneous but are almost exactly antipodal made scientists wonder if that wasn't a coincidence.

Apparently, the thought is this.  When the Chicxulub Impact occurred, it sent huge shock waves through the Earth, which propagated both through the mantle and along the crust.  When those waves had traveled all the way around (or through) the Earth, they converged on a single point, almost like a magnifying glass bringing rays of sunlight focusing on one spot.  This reinforced the waves, ringing the Earth like a bell, and the crust destabilized...

... cracking open and creating one of the largest volcanic eruptions ever.

So the whole thing becomes a double whammy, and not because of an unfortunate accident.  It seems likely that one event caused the other, and also explains why species that lived in what is now Asia were affected just as much by the extinction as ones that were near the collision itself.  Seems kind of unfair, doesn't it?  The meteorite collides with the Earth, causing massive devastation in the Western Hemisphere, and the critters in the Eastern Hemisphere only had a few minutes to gloat before a massive earthquake launched an event that did them in, too.

"Both the impact and Deccan volcanism can produce similar environmental effects, but these are occurring on vastly differing timescales," study co-author Courtney Sprain said.  "Therefore, to understand how each agent contributed to the extinction event, assessing timing is key."

There you have it.  Yet another reason why we wouldn't want the Earth to get hit by a huge asteroid, if you needed another one.  Kind of dwarfs the earthquakes and volcanoes we've had recently, doesn't it?  Also makes me realize how fragile the biosphere is, and that a sudden and unforeseen event can trigger enormous destruction -- one a bolt from the sky, the other from the deepest regions of the Earth's mantle.

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This week's Skeptophilia book recommendation is a tour-de-force for anyone who is interested in biology -- Richard Dawkins's The Ancestor's Tale.  Dawkins uses the metaphoric framework of The Canterbury Tales to take a walk back into the past, where various travelers meet up along the way and tell their stories.  He starts with humans -- although takes great pains to emphasize that this is an arbitrary and anthropocentric choice -- and shows how other lineages meet up with ours.  First the great apes, then the monkeys, then gibbons, then lemurs, then various other mammals -- and on and on back until we reach LUCA, the "last universal common ancestor" to all life on Earth.

Dawkins's signature lucid, conversational style makes this anything but a dry read, but you will come away with a far deeper understanding of the interrelationships of our fellow Earthlings, and a greater appreciation for how powerful the evolutionary model actually is.  If I had to recommend one and only one book on the subject of biology for any science-minded person to read, The Ancestor's Tale would be it.

[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]

Science shorts

After the last three days' depressing posts, I thought it was once again time to retreat to my happy place, which is: cool new scientific research.  So, for your reading entertainment, here are some early-summer shorts.

[Image licensed under the Creative Commons marcore! from Hong Kong, China, Board shorts 4, CC BY 2.0]

No, not those kind of shorts.  The scientific variety.

First, we have some research that appeared last week in the Journal of Applied Research in Memory and Cognition, done by Julia Soares and Benjamin Storm of the University of California.  In their paper, entitled, "Forget in a Flash: A Further Investigation of the Photo-Taking Impairment Effect," what Soares and Storm found that for reasons still unknown, taking a photo of something impairs your ability to remember it -- even if you know that you won't have access to the photo later.

The authors write:

A photo-taking-impairment effect has been observed such that participants are less likely to remember objects they photograph than objects they only observe.  According to the offloading hypothesis, taking photos allows people to offload organic memory onto the camera's prosthetic memory, which they can rely upon to “remember” for them.  We tested this hypothesis by manipulating whether participants perceived photo-taking as capable of serving as a form of offloading.  In [our] experiments, participants exhibited a significant photo-taking-impairment effect even though they did not expect to have access to the photos.  In fact, the effect was just as large as when participants believed they would have access to the photos.  These results suggest that offloading may not be the sole, or even primary, mechanism for the photo-taking-impairment effect.

The authors were interviewed by Alex Fradera for the Research Digest of the British Psychological Society, and there's a possible explanation for the phenomenon, although it's still speculative.  Fradera writes:

Soares and Storm have a speculative second interpretation.  They suggest that the effort involved in taking a photo – getting the framing right, ensuring the lens is in focus – leads to the sense that you’ve done a good job of encoding the object itself, even though you have been focusing more on peripheral features.  So you’re not mentally slacking-off because you think the camera has it covered – but because you think you already have.  It may be relevant that people who take photographs at events report afterwards feeling more immersed in the experience, which would tally more with this explanation than the disengagement-due-to-fiddling idea.  In any case this is further evidence that those of us who approach exciting life events through the lenses of our electronic devices may be distancing ourselves from fuller participation.

From the Department of Geophysics at the University of Texas comes a study of the most famous (although not, by a long shot, the largest) mass extinction event -- the Cretaceous-Tertiary Extinction of 65 million years ago, which took out the dinosaurs, with the exception of the ancestors of today's birds.  The accepted explanation of the event is a collision by a massive meteorite near what is now the Yucatán Peninsula, forming the Chicxulub Crater.

A long-unanswered question about mass extinctions such as this one is how fast life rebounded.  The problem is that the difference between a thousand, ten thousand, and a hundred thousand years in the geological record isn't that great, so the error rate for any estimates were bound to be high.  But now, geophysicists Chris Lowery, Gail Christeson, Sean Gulick, and Cornelia Rasmussen, working with Timothy Bralower, a micropaleontologist at Pennsylvania State University, have found evidence that narrows that window down -- and surprisingly, shows that life recovered pretty quickly.

The key was finding a sediment core that contained 76 centimeters of brown limestone that came from the years immediately following the impact.  It contained debris from the event, including crystals of "shocked quartz" (quartz crystals showing signs of sudden, extreme temperatures and pressures).  And what the researchers found was that a little as a few thousand years, the ecosystem was beginning to rebound.

"You can see layering in this core, while in others, they’re generally mixed, meaning that the record of fossils and materials is all churned up, and you can’t resolve tiny time intervals," Bralower said.  "We have a fossil record here where we’re able to resolve daily, weekly, monthly, yearly changes."

Speaking of catastrophes, a fascinating piece of research from Stanford University anthropologists Tian Chen Zeng, Alan Aw, and Marcus Feldman gives us a possible explanation for a peculiar calamity that the human race experienced only seven thousand years ago.  By analyzing the genetic diversity among human Y-chromosomal DNA (inherited only father-to-son) and comparing it to the diversity in mitochondrial DNA (inherited only mother-to-child), they found something decidedly odd; the data suggested a serious genetic bottleneck -- but one that affected only males.

The difference was huge.  Zeng et al. showed that the disparity would only make sense if there was a point about seven thousand years ago when there was one male with surviving descendants for every seventeen females.

Feldman writes, in a press release to EurekAlert!:

After the onset of farming and herding around 12,000 years ago, societies grew increasingly organized around extended kinship groups, many of them patrilineal clans - a cultural fact with potentially significant biological consequences. The key is how clan members are related to each other.  While women may have married into a clan, men in such clans are all related through male ancestors and therefore tend to have the same Y chromosomes.  From the point of view of those chromosomes at least, it's almost as if everyone in a clan has the same father. 

That only applies within one clan, however, and there could still be considerable variation between clans.  To explain why even between-clan variation might have declined during the bottleneck, the researchers hypothesized that wars, if they repeatedly wiped out entire clans over time, would also wipe out a good many male lineages and their unique Y chromosomes in the process.

So as weird as it sounds, if you go back a few thousand years, we all have far fewer unique male ancestors than unique female ancestors.


Last, I would be remiss if I didn't make at least a brief mention of research that appeared in the Journal of Clinical Endocrinology and Metabolism last week.  Authored by Audrey J. Gaskins, Rajeshwari Sundaram, Germaine M. Buck Louis, and Jorge E. Chavarro, the paper was entitled "Seafood Intake, Sexual Activity, and Time to Pregnancy," and amongst its conclusion was that the quantity of seafood eaten correlates positively with the number of times per month people have sex.

The researchers speculate that the reason may be the higher quantity of long-chain omega-3 fatty acids, common in seafood, has an effect on the reproductive hormones, increasing sex drive.  It does, however, make me wonder how anyone thought of correlating these, but my puzzlement is probably indicative of why I never went into research.

In any case, I thought it was interesting.  And makes me glad I brought leftover scampi for lunch.  Hope springs eternal, you know?

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This week's recommended book is one that blew me away when I first read it, upon the urging of a student.  By groundbreaking neuroscientist David Eagleman, Incognito is a brilliant and often astonishing analysis of how our brains work.  In clear, lucid prose, Eagleman probes the innermost workings of our nervous systems -- and you'll learn not only how sophisticated it is, but how easy it can be to fool.