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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Titans of the ocean

As far as scary critters go, you'd have to look hard to find one scarier than the elasmosaurs.

If you've never seen an artist's reconstruction of one of these beasts, picture something like the body of a sea turtle, with an incredibly long neck and snake-like head, with lots of big, nasty, pointy teeth.  The largest ones reached a length of twelve meters, and a weight of several tons.  The conventional wisdom is that they "mostly ate crustaceans and mollusks," but my feeling is that if they encountered a swimmer, the result would be something like what happened in the movie Jaws, only worse.

Artist's reconstruction of Thalassomedon haningtoni, a late Cretaceous elasmosaur [Image licensed under the Creative Commons DiBgd, Thalassomedon haningtoni, CC BY-SA 4.0]

Fortunately for us, they are one of the groups that ran afoul of the Chicxulub Meteorite Impact 66 million years ago, and they all became extinct, unless you believe in the Loch Ness Monster, which would definitely be an elasmosaur if it actually existed.

This comes up because last week, paleontologists announced that they have unearthed a nearly-complete fossil of the largest-known elasmosaur, Aristonectes, which when alive would have been thirteen meters long and weighed twelve tons.  The fossil was found on Seymour Island in 1989, but was only excavated now because Seymour Island is at the tip of the Antarctic Peninsula, and is windswept, cold, hostile, and hard to get to even during the brief Antarctic summer.  The research team, led by José O’Gorman, a paleontologist with the National Scientific and Technical Research Council of Argentina (CONICET) who is based at the Museum of La Plata near Buenos Aires, has finished the excavation and submitted their results to the journal Cretaceous Research.

What to me is most fascinating about this specimen -- besides its sheer size, which is eye-opening enough -- is that it dates to only thirty thousand years before the K-T Extinction, which (palenontologically speaking) is barely any time at all.  So these big guys were thriving (and diversifying) right up to the moment the big crash occurred -- further evidence that the meteorite was the trigger to the entire extinction event.

O'Gorman says that the work to recover the specimen was grueling.  It began in 2012, proceeding at a snail's pace because the site was only accessible a couple of weeks a year, in late January and early February, and sometimes not even then if there was an unexpected storm. "The weather is one of the problems," O'Gorman said.  "The weather controls all.  Maybe one day you can work, and the next day you cannot because you have a snowstorm."

But their painstaking labor has finally paid off, and given us a picture of a truly awesome critter who was swimming around the oceans right on the verge of one of the "Big Five" extinction events.  Like I said, as a swimmer and scuba diver, I'm just as happy they're not around any more, but getting a glimpse of one of the largest aquatic predators the Earth has ever produced is enough to leave me in awe.
 
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This week's Skeptophilia book recommendation is a little on the dark side; Jared Diamond's riveting book Collapse: How Societies Choose to Fail or Succeed.  Starting with societies that sowed the seeds of their own destruction -- such as the Easter Islanders, whose denuding of the landscape led to island-wide ecological collapse -- he focuses the lens on the United States and western Europe, whose rampant resource use, apparent disregard for curbing pollution, and choice of short-term expediency over long-term wisdom seem to be pushing us in the direction of disaster.

It's not a cheerful book, but it's a very necessary one, and is even more pertinent now than when it was written in 2005.  Diamond highlights the problems we face, and warns of that threshold we're approaching toward catastrophe -- a threshold that is so subtle that we may well not notice it until it's too late to reverse course.

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

Snapshot of a very bad day

Some of you have probably bumped into articles in the last week or so about a phenomenal discovery in paleontology -- a fossil bed in North Dakota that may have been created the day the Chicxulub Meteor Strike occurred, 66 million years ago.  This single event is thought to have flash-fried everything in the southern half of what is now North America, changed climates worldwide, and was the death blow to the dinosaurs, with the exception of the lineage that led to modern birds.

The deposit contains exquisitely preserved remains of a variety of fish, plants, dinosaurs, and mollusks.  The gills of the fish contained huge numbers of tektites -- tiny spheres of glass formed during a meteorite collision and ejected into the atmosphere.  The impact is thought to have caused a magnitude 10 earthquake (almost unimaginable to me), which took the shallow ocean that crossed what is now the central United States and "agitated it like a washing machine" -- creating a seiche, a standing wave like the sloshing of water in a giant bathtub.

The seiche caused the repeated exposure and inundation of shallow regions, and while exposed, the stranded animals were subjected to a rain of tektites and other debris thrown up by the collision.

"This is the first mass death assemblage of large organisms anyone has found associated with the K-T boundary," Robert DePalma, curator of paleontology at the Palm Beach Museum of Natural History in Florida and a doctoral student at the University of Kansas, said in a press release.  "At no other K-T boundary section on Earth can you find such a collection consisting of a large number of species representing different ages of organisms and different stages of life, all of which died at the same time, on the same day."

One of the fish from the Hell Creek fossil bed

"The seismic waves start arising within nine to ten minutes of the impact, so they had a chance to get the water sloshing before all the spherules (small spheres) had fallen out of the sky," said Mark Richards, professor emeritus of earth and planetary science at the University of California - Berkeley.  "These spherules coming in cratered the surface, making funnels — you can see the deformed layers in what used to be soft mud — and then rubble covered the spherules.  No one has seen these funnels before...  You can imagine standing there being pelted by these glass spherules.  They could have killed you."

It's amazing to think that if these scientists are correct -- and the consensus amongst paleontologists is that they are -- we're seeing a remnant of a catastrophe initiated at a single moment in time.  The simulations of what happened are astonishing enough:

But somehow, to see the remains of animals that were directly killed by the collision, who were there when it happened, gives it an immediacy that is stunning.

So this is cool enough, right?  But what makes it even more personal for me is that one of the researchers who has worked the Hell Creek fossil bed, and was a co-author of the paper...

... is Loren Gurche, who is a former student of mine.

I distinctly remember Loren's contributions to my AP Biology class -- whenever the topic was prehistory, I always deferred to his greater knowledge.  Even then, when he was in 11th grade, he clearly knew way more paleontology than I did, or probably, than I ever would.  The presence of a true expert enriched both my experience and the other students', and it's thrilling to see that he is making significant contributions in a field about which he is so deeply passionate.

So the whole thing is doubly cool for me to read about.  I'm looking forward to more discoveries by Loren and the team he's working with, although it must be said it'll be hard to top this one.  This snapshot of one of the worst disasters ever to strike the Earth is the find of a lifetime.

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This week's Skeptophilia book recommendation combines science with biography and high drama.  It's the story of the discovery of oxygen, through the work of the sometimes friends, sometimes bitter rivals Joseph Priestley and Antoine Lavoisier.   A World on Fire: A Heretic, an Aristocrat, and the Race to Discover Oxygen is a fascinating read, both for the science and for the very different personalities of the two men involved.  Priestley was determined, serious, and a bit of a recluse; Lavoisier a pampered nobleman who was as often making the rounds of the social upper-crust in 18th century Paris as he was in his laboratory.  But despite their differences, their contributions were both essential -- and each of them ended up running afoul of the conventional powers-that-be, with tragic results.

The story of how their combined efforts led to a complete overturning of our understanding of that most ubiquitous of substances -- air -- will keep you engaged until the very last page.

[Note:  If you purchase this book by clicking on the image/link below, part of the proceeds will go to support Skeptophilia!]

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!]

Myths, mammals, and extinctions

It's interesting how the scientific version of urban legends can be incorporated into people's knowledge of how things work, and become so entwined that most folks don't even know which bits are true and which aren't.

Stephen Jay Gould riffed on this theme in his essay "The Case of the Creeping Fox Terrier Clone," which appeared first in Natural History and was later published in his essay collection Bully for Brontosaurus.  He looks at the claim that an early horse species, Hyracotherium, was "the size of a fox terrier" -- something that Gould found quoted in dozens of books on prehistoric animals (and which has therefore been used as a gauge of the animal's size in countless classrooms).  It turns out that it originated with a paleontologist, O. C. Marsh, who said Hyracotherium was the "size of a fox" -- a significant underestimate, as both foxes and fox terriers top out at around twenty pounds, and Hyracotherium weighed in at something closer to sixty.  But the analogy stuck, and people continued to pass it along without checking its veracity -- giving us the impression of tiny dog-sized horses, lo unto this very day.

Another example of this, from the same field, is that mammals were small, few in number, and low in biodiversity until along came a meteorite that for some reason selectively killed all the dinosaurs, leaving the mammals to throw a great big party and evolve like mad into the species we have around today.  This is incorrect on a variety of levels:

1. The K-T (Cretaceous/Tertiary) Extinction of 66 million years ago seems to have been caused by a double whammy -- the aforementioned meteorite, which left the Chicxulub Crater in what is now the Gulf of Mexico, and the formation of the Deccan Traps, a lava field from a colossal supervolcano eruption, all the way around the Earth in what is now India.
2. Dinosaur biodiversity had been decreasing for some time before the K-T Extinction, and in fact by some estimates was already down 40% from its peak during the mid-Cretaceous.
3. ...however...  All the dinosaurs didn't go extinct 66 million years ago, and I'm not talking about Nessie, Ogopogo, and Mokélé-Mbembe.  We still have dinosaurs around, we just call 'em birds.  The evidence is now incontrovertible.  Think about that next time you're putting out sunflower seeds for the chickadees.
4. The extinction hit pretty much every taxon that existed at the time.  The hardest-hit were large carnivores -- a vulnerable spot in the food chain at the best of times -- but no one escaped unscathed.  In fact, one group that got wiped out completely were the ammonites, a cephalopod mollusk that had thrived for 350 million years before getting clobbered during the K-T Extinction.
5. Most pertinent to this post, the mammals weren't just skulking around waiting for their opportunity; they'd been thriving alongside dinosaurs since the Triassic Period, 154 million years earlier.  This was the topic of a paper released a couple of months ago in Biology Letters by Tiago Bosisio Quental of the University of São Paulo and Mathias Pires of the University of Campinas.

What Quental and Pires did is a thorough survey of mammalian fossils, analyzing biodiversity as a function of time in three of the four big lineages of mammals -- Eutherians (most of the mammals you're familiar with), Metatherians (marsupials), and Multituberculates (an odd group of rodent-like mammals that were only distantly related to the rest of Class Mammalia, and which were one of the most common groups of mammals for almost two hundred million years).  They didn't include the fourth lineage -- the Monotremes, or egg-laying mammals -- only because they are extremely rare in the fossil record.

A late Cretaceous multituberculate, Catopsbaatar [Image licensed under the Creative Commons, Artwork by Bogusław Waksmundzki. Article by Zofia Kielan-Jaworowska and Jørn H. Hurum, Catopsbaatar, CC BY 2.0]

What they found -- predictably -- is that the dynamics of the extinction, and the years following it, is far more complex than it's usually represented.  "All these mass extinction episodes are heterogeneous," study co-author Pires said.  "They occurred for different reasons and unfolded in different ways.  Their impact on life forms was not absolute but relative.  Some groups suffered more, others less.  Some disappeared, while others took advantage of the new environmental conditions after the catastrophe to diversify rapidly."

Even within groups, the extinction didn't have uniform effects.  "Extinctions were concentrated among the specialized carnivorous metatherians and insectivorous eutherians," Pires said, "whereas more generalized eutherians and multituberculates survived and maintained higher diversity."

He added, "This means that studies of macroevolutionary phenomena focusing on broad taxonomic groups may miss a much richer macroevolutionary history, which can be perceived only at finer taxonomic scales."

Which can more generally be summed up as "the simple explanation is usually wrong."  It'd be nice if things weren't so complex, especially for we non-scientists.  But like Gould's fox-terrier-horse, many of these oversimplifications are flat-out incorrect -- and the truth is so much more interesting.

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This week's Skeptophilia book recommendation is one of personal significance to me -- Michael Pollan's latest book, How to Change Your Mind.  Pollan's phenomenal writing in tours de force like The Omnivore's Dilemma and The Botany of Desire shines through here, where he takes on a controversial topic -- the use of psychedelic drugs to treat depression and anxiety.

Hallucinogens like DMT, LSD, ketamine, and psilocybin have long been classified as schedule-1 drugs -- chemicals which are off limits even for research except by a rigorous and time-consuming approval process that seldom results in a thumbs-up.  As a result, most researchers in mood disorders haven't even considered them, looking instead at more conventional antidepressants and anxiolytics.  It's only recently that there's been renewed interest, when it was found that one administration of drugs like ketamine, under controlled conditions, was enough to alleviate intractable depression, not just for hours or days but for months.

Pollan looks at the subject from all angles -- the history of psychedelics and why they've been taboo for so long, the psychopharmacology of the substances themselves, and the people whose lives have been changed by them.  It's a fascinating read -- and I hope it generates a sea change in our attitudes toward chemicals that could help literally millions of people deal with disorders that can rob their lives of pleasure, satisfaction, and motivation.

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