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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Weighty matter

Springboarding off yesterday's post, about a discovery of fossils that seem to have come from animals killed the day the Chicxulub Meteorite struck 66 million years ago, today we have a paper in arXiv that looks at why the meteorite hit in the first place.

When you're talking about an event that colossal, I suppose it's natural enough to cast about for a reason other than just shrugging and saying, "Shit happens."  But even allowing for that tendency, the solution landed upon by Leandros Perivolaropoulos, physicist at the University of Ioannina (Greece), seems pretty out there.

Perivolaropoulos attributes the meteorite strike to a sudden increase in Newton's gravitational constant, G -- the number that relates the ratio of the product of two masses and the square of the distance between them to the magnitude of the gravitational force:

The generally accepted value for G is 6.67430 x 10^-11 m^3 kg^-1 s^-2.  Being a constant, the assumption is that it's... constant.  And always has been.

Perivolaropoulos's hypothesis is that millions of years ago, there was a sudden jump in the value of G by about ten percent.  As you can tell from the above equation, if you keep the masses and the distance between them constant, F is directly proportional to G; if G increased by ten percent, so would the magnitude of the gravitational force.  His thought is that this spike in the attractive force caused the orbits of asteroids and comets to destabilize, and sent them hurtling in toward the inner Solar System.  The result: collisions that marked the violent, sudden end of the Mesozoic Era and the hegemony of the dinosaurs.

To be fair to Perivolaropoulos, his surmise is not just based on a single meteorite collision.  He claims that this increase in G could also resolve the "Hubble crisis" -- the fact that two different measures of the rate of the expansion of the universe generate different answers.  The first, using the cosmic microwave background radiation, comes up with a value of 67.8 kilometers/second/megaparsec; the second, from using "standard candles" like Cepheid variables and type 1A supernovas, comes up with 73.2.  (You can read an excellent summary of the dispute, and the current state of the research, here.)

[Image is in the Public Domain courtesy of NASA]

Perivolaropoulos says that his hypothesis takes care of both the Hubble crisis and the reason behind the end-Cretaceous meteorite collision in one fell swoop.

Okay, where to start?

There are a number of problems with this conjecture.  First -- what on earth (or off it) could cause a universe-wide alteration in one of the most fundamental physical constants?  Perivolaropoulos writes, "Physical mechanisms that could induce an ultra-late gravitational transition include a first order scalar tensor theory phase transition from an early false vacuum corresponding to the measured value of the cosmological constant to a new vacuum with lower or zero vacuum energy."  Put more simply, we're looking at a sudden phase shift in space/time, analogous to what happens when the temperature of water falls below 0 C and it suddenly begins to crystallize into ice.  But why?  What triggered it?

Second, if G did suddenly increase by ten percent, it would create some serious havoc in everything undergoing any sort of gravitational interaction.  I.e., everything.  Just to mention one example, the relationship between the mass of the Sun, the velocity of a planet, and the distance between the two is governed by the equation

 

So if the Earth (for example) experienced a sudden increase in the value of G, the radius of its orbit would (equally suddenly) decrease by ten percent.  Moving the Earth ten percent closer to the Sun would, of course, lead to an increase in temperature.  Oh, he says, but that actually happened; ten million years after the extinction of the dinosaurs we have the Paleocene-Eocene Thermal Maximum, when the temperatures went up by something like 7 C.  However, the PETM is sufficiently explained by a fast injection of five thousand gigatons of carbon dioxide into the atmosphere and oceans, likely triggered by massive volcanism in the North Atlantic Igneous Province -- and there's significant evidence of a carbon dioxide spike from stratigraphic evidence.  No need for the Earth to suddenly lurch closer to the Sun.

It wouldn't just affect orbits, of course.  Everything would suddenly weigh ten percent more.  It would take more energy to run, jump, even stand up.  Mountain building would slow down.  Anything in freefall -- from boulders in an avalanche to raindrops -- would accelerate faster.  Tidal fluctuations would decrease (although with the Moon now closer to the Earth, maybe that one would balance out).  

Also, if G did increase everywhere -- it's called the "universal gravitational constant," after all -- then the same thing would have happened simultaneously across the entire universe.  Then, for some reason, there was a commensurate decrease sometime between then and now, leveling G out at the value we now measure.  So we really need not one, but two, mysterious unexplained universal phase transitions, as if one weren't bad enough.

Then there's the issue that the discrepancy in the measurement in the Hubble constant isn't as big as all that -- it's only 3.4 sigma, not yet reaching the 5 sigma threshold that is the touchstone for results to be considered significant in (for example) particle physics.  Admittedly, 3.4 sigma isn't something we can simply ignore; it definitely deserves further research, and (hopefully) an explanation.  But explaining the Hubble constant measurement issue by appeal to an entirely different set of discrepant measurements that have way less experimental support seems like it's not solving anything, it's just moving the mystery onto even shakier ground.

Last, though, I come back to two of the fundamental rules of thumb in science; Ockham's razor (the explanation that adequately accounts for all the facts, and requires the fewest ad hoc assumptions, is most likely to be correct) and the ECREE principle (extraordinary claims require extraordinary evidence).  Perivolaropoulos's hypothesis not only blasts both of those to smithereens, it postulates a phenomenon that occurred once, millions of years ago, then mysteriously reversed itself, and along the way left behind no other significant evidence.

I hate to break out Wolfgang Pauli's acerbic quote again, but "This isn't even wrong."

Now, to be up front, I'm not a physicist.  I have a distantly-remembered B.S. in physics, which hardly qualifies me to evaluate an academic paper on the subject with anything like real rigor.  So if there are any physicists in the studio audience who disagree with my conclusions and want to weigh in, I'm happy to listen.  Maybe there's something going on here that favors Perivolaropoulos's hypothesis that I'm not seeing, and if so, I'll revise my understanding accordingly.

But until then, I think we have to mark the Hubble crisis as "unresolved" and the extinction of the dinosaurs as "really bad luck."

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Springtime collision

I've written here before about the rather sobering topic of mass extinctions, and from what reading I've done on the topic, it always leaves me thinking about how fragile Earth's ecosystems are.  Most of the biggest extinctions were not due to a single cause, though; for example, the Ordovician-Silurian extinction of about 445 million years ago seems to have been touched off by plate tectonics -- the massive southern continent of Gondwana meandered across the south pole, leading to ice cap formation, massive glaciation, and a drop in sea level.  However, there followed a huge drop in atmospheric oxygen and spike in sulfur, leading to worldwide oceanic anoxia.  The result: an estimate 60% mortality rate in species all over the Earth.

Anoxia is also thought to have played a role in the largest mass extinction ever, the Permian-Triassic extinction of 252 million years ago.  This one, however, seems to have begun with a catastrophic volcanic eruption that boosted the carbon dioxide in the atmosphere, and thus the temperature.  Temperature is inversely related to oxygen solubility, so as the oceans warmed, what oxygen was left in the air didn't dissolve as well, and nearly everything in the oceans died (a mortality rate estimated at an almost unimaginable 95%).  This caused an explosive growth in anaerobic bacteria, pumping both carbon dioxide and methane into the atmosphere.  The average temperature skyrocketed by as much as ten degrees Celsius.

Even the smaller extinctions seldom come from one cause.  I wrote recently about the Eocene-Oligocene extinction, which wiped out a good many of Africa's mammal species (our ancestors survived, fortunately for us), and was apparently an evil confluence of three unrelated events -- rapid cooling of the climate after the Paleocene-Eocene Thermal Maximum, a massive meteorite collision near what is now Chesapeake Bay, and explosive volcanism in Ethiopia.

The exception to the rule seems to be the most famous extinction of all, the Cretaceous-Tertiary extinction of 66 million years ago.  The one that ended the hegemony of the dinosaurs.  I always find it wryly amusing when the dinosaurs are described as some kind of evolutionary dead-end, as if their failure to survive to today is indicative that they were inferior or maladapted.  In fact, the dinosaurs as such were the dominant group of terrestrial animals for almost two hundred million years -- from the late Permian to the end of the Cretaceous -- and that's not counting birds, which are (frankly) dinosaurs, too.  That means if you consider the earliest modern humans to have lived in Africa on the order of three hundred thousand years ago, the dinosaurs kind of ran the planet for over six hundred times longer than we've even existed.

And in the blink of an eye, everything changed.  Far from being an evolutionary cul-de-sac, the dinosaurs were doing just fine, when a meteor ten kilometers in diameter slammed into the Earth near what is now the Yucatán Peninsula of Mexico.  And now scientists have been able to pinpoint not only where the collision happened, but what time of year -- the middle of the Northern Hemisphere's spring.

The Chicxulub Impact, as visualized by artist Donald E. Davis [image is in the Public Domain courtesy of NASA]

Paleontologists working in North Dakota have found a rich fossil site that was created on that fateful day.  Pre-collision, the area was a wet lowland forest with a shallow river.  The slow-moving water was the home of paddlefish and sturgeon, swimming slowly and nosing around in the mud for food.  Then, three thousand kilometers away, the meteor struck.  The shock wave ejected a sheet of superheated steam and molten rock skyward; the impact, which occurred in what was (and still is) a shallow marine region, generated a tsunami the likes of which I can't even imagine.  The southern part of North America got flash-fried by the heat generated by the strike; only a few minutes later, it was followed by a wall of water the height of a skyscraper that swept across the land at an estimated five hundred kilometers an hour.

The first thing the fish would have noticed, though, is a rain of tiny globs of molten glass that sizzled as they hit the water and settled out, coating the riverbed and clogging their gills.  Then the tsunami hit, burying the site under thick layers of sediment.  By the time things calmed down, most of the living things in North America were dead, their fossils left behind as a near-instantaneous photograph of one of the worst days the Earth has ever seen.

It's the quickness of the event that allowed scientists to figure out when it happened.  Paddlefish bones form growth layers -- a little like the rings inside a tree trunk -- and all of the paddlefish fossils from the site show an increasing rate of growth, but not yet at its annual peak (which occurs in the warmest parts of summer).  The Chicxulub meteorite seems to have struck the Earth in April or May.

This may be another reason why the Northern Hemisphere flora and fauna took a much bigger hit than the ones in the Southern Hemisphere.  The initial explanation was that the meteor struck the Earth at an angle, on with a trajectory on the order of forty-five degrees south of vertical, so the shower of molten debris mostly got blasted northward.  (This may well be true; the current research doesn't contradict that assessment.)  But if the strike occurred in the Northern Hemisphere's spring, when plants are leafing out and flowering, and animals increasing in activity, it would have been catastrophic.  The ones in the Southern Hemisphere, heading into fall and winter, would have been in the process of powering down and moving toward dormancy and hibernation, and may have been more insulated from the effects.

Besides the obvious fascination of an event so cataclysmic, it's just stupendous that we can analyze the evidence so finely that we can determine what time of year it occurred, 66 million years later.  It also highlights how suddenly things can change.  The dinosaurs had been around for two hundred million years, surviving not only the colossal Permian-Triassic extinction but the smaller (but still huge) end-Triassic extinction, that took out thirty percent of the species on Earth.  In one particular April of 66 million years ago, a quick look around would have led you to believe that everything was fine, and that the dinosaurs and other Mesozoic critters weren't going anywhere.

A day later, the entire face of the Earth had changed forever.

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Dinosaur redux

For me, one of the coolest things about science is that even once you think you've got something pretty well figured out, you can always find new interesting pieces of the puzzle.

For example, take dinosaurs, which we've known a good bit about for a long while, starting with Mary Anning's discoveries along the "Jurassic Coast" of Dorset, England in the early nineteenth century.  Even the kids' books when I was growing up back in the 1960s and 1970s had a lot of pretty decent information.  Although some of the reconstructions of skeletons, and (especially) our knowledge of the soft tissue that covered it, has changed since that time, it wasn't like I had to completely relearn the science when I studied it more seriously.

That said, we're still learning new stuff and adding to the picture.  Just this week we had two new papers that have sharpened the focus on our understanding of dinosaur evolution -- the first about the mid-Jurassic peak in dinosaur diversity and size, and the second about the event that wiped the entire lineage out, with the exception of the ones we now call birds.

The first paper is from Proceedings of the Royal Society B, and is titled "Extinction of Herbivorous Dinosaurs Linked to Early Jurassic Global Warming Event."  The paper was written by a team led by Diego Pol, paleontologist at the Paleontological Museum Egidio Feruglio in Trelew, Argentina, and looked at a hitherto-unexplained overturning of Jurassic fauna that made way for the rise of the sauropods -- the largest land animals that have ever lived.

Skeleton of Apatosaurus [Image licensed under the Creative Commons Tadek Kurpaski from London, Poland, Louisae, CC BY 2.0]

The early Jurassic had a high dinosaur diversity, but then toward the middle of the period something happened, and a good many of the early Jurassic dinosaurs vanished.  They were replaced by behemoths like the familiar Brachiosaurus and the less-well-known but hilariously-named Supersaurus, which measured an almost unimaginable 33 meters from tip to tail.  (Even better, though, is the name Dreadnoughtus, which was shorter than Supersaurus -- "only" 26 or so meters long -- but is thought to be the heaviest land animal ever, on the order of thirty metric tonnes.)

So what caused the replacement of the earlier species by the giants?  Pol and his team found what they think is the smoking gun, a series of massive volcanic eruptions in southern Gondwanaland (what is now South America and Africa), which spiked the carbon dioxide content of the air, boosting the average temperature and dropping the pH of ocean water.  

The perturbation of the climate affected the plants first.  Earlier groups, like seed ferns and other smaller herbaceous plants, were replaced by conifers, which have tough, lignified stems, small needles or scales instead of leaves, and thick waxy cuticles to prevent water loss.  The problem is -- if you're an early Jurassic herbivorous dinosaur -- having evolved to eat seed ferns, you're not going to do so well trying to munch pine needles.

So as it always does, the change to the base of the food web percolated its way up to the top.  The early dinosaurs were replaced by big sauropods, who had grinding teeth (so tough plant material could be thoroughly pulverized before swallowing) and large stomachs (where food could sit and digest for a long time, extracting all the nutritive value possible).  The result was the arrival on the scene of monsters like Supersaurus and Dreadnoughtus and their cousins, which were the dominant land herbivores for a good hundred million years thereafter.

Sometimes new evidence results in our having to revise our previous models, overturning what we thought we knew.  Take, for example, the research that appeared this week in Royal Society Open Science that conclusively put to rest a commonly-held idea -- that by the time the Chicxulub Meteorite hit the Earth 66 million years ago, dinosaurs were already in a steep decline, so they would have disappeared anyhow, even without the massive impact that was the final death blow.

In "Dinosaur Diversification Rates Were Not in Decline Prior to the K-Pg Boundary," by a team led by Joseph Bonsor of the London Natural History Museum and the University of Bath, we find out that the dinosaurs were actually doing okay before the meteorite hit.  Far from being in decline, they would have been very likely to retain their position as the dominant animals on Earth well into the Cenozoic Era -- with effects on mammalian evolution that can only be imagined.

Bonsor, as befits a good scientist, is cautious about overconcluding.  "The main point of what we are saying is that we don't really have enough data to know either way what would have happened to the dinosaurs," Bonsor said in a press release from the Natural History Museum.  "Generally in the fossil record there is a bias towards a lack of data, and to interpret those gaps in the fossil record as an artificial decline in diversification rates isn't what we should be doing.  Instead we've shown that there is no strong evidence for them dying out, and that the only way to know for sure is to fill in the gaps in the fossil record."

But in the absence of positive evidence for a decline, we're thrown back to the null hypothesis; that they weren't in imminent danger of extinction.  So the whole idea of the dinosaurs as some kind of "failed experiment" in evolution is clearly wrong.  Not only did they kind of run things for a good two hundred million years -- which, by comparison, is something like a thousand times longer than we've been around -- they would probably have persisted for a good long while had a giant rock not interfered.

Me, I always want to know "what if?"  I think it comes from being a novelist; I'm always wanting to play around with reality and see what happens.  If the dinosaurs had stuck around for a long time rather than dying out 66 million years ago, it's hard to see how the rise of mammals -- and ultimately, us -- would have occurred.  Mammals had been around for a long while before the Chicxulub Impact, but they were mostly small, presumably kept that way both by the big carnivores and by competition with herbivores much larger than themselves.  So what would the Earth look like today?

Super-intelligent dinosaurs?  Maybe.  Evolution doesn't always point in the direction of "bigger and smarter;" it's the law of whatever works.  So as fun as it is to speculate, to be fair we have to side with Bonsor and say we just don't know.

Anyhow, that's our look back into the distant past for today.  Cool that we're still assembling new views of an old branch of biology.  Further reinforcing my opinion that if you're interested in science, you will never ever be bored.

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This week's Skeptophilia book-of-the-week is one that has raised a controversy in the scientific world: Ancient Bones: Unearthing the Astonishing New Story of How We Became Human, by Madeleine Böhme, Rüdiger Braun, and Florian Breier.

It tells the story of a stupendous discovery -- twelve-million-year-old hominin fossils, of a new species christened Danuvius guggenmosi.  The astonishing thing about these fossils is where they were found.  Not in Africa, where previous models had confined all early hominins, but in Germany.

The discovery of Danuvius complicated our own ancestry, and raised a deep and difficult-to-answer question; when and how did we become human?  It's clear that the answer isn't as simple as we thought when the first hominin fossils were uncovered in Olduvai Gorge, and it was believed that if you took all of our millennia of migrations all over the globe and ran them backwards, they all converged on the East African Rift Valley.  That neat solution has come into serious question, and the truth seems to be that like most evolutionary lineages, hominins included multiple branches that moved around, interbred for a while, then went their separate ways, either to thrive or to die out.  The real story is considerably more complicated and fascinating than we'd thought at first, and Danuvius has added another layer to that complexity, bringing up as many questions as it answers.

Ancient Bones is a fascinating read for anyone interested in anthropology, paleontology, or evolutionary biology.  It is sure to be the basis of scientific discussion for the foreseeable future, and to spur more searches for our relatives -- including in places where we didn't think they'd gone.

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

Life finds a way

I've dealt more than once here at Skeptophilia with the repeated mass extinctions the Earth has undergone.  Part of this is that I have an admitted fascination with things that are big and powerful and can kill you.  These include:

• tornadoes and hurricanes
• lightning
• earthquakes
• volcanoes
• death asteroids from outer space

The latter is thought to have been the prime mover of the Cretaceous Extinction, which occurred 66 million years ago and killed an estimated 75% of the species on Earth, including all of the large dinosaurs (the exception being the lineage that led to modern birds).  Here's a cool, if terrifying, simulation of what it'd be like if the Earth got hit by an asteroid five hundred kilometers in diameter (the Chicxulub Meteorite, which caused the extinction, is estimated to be about a tenth that diameter, so you can scale down your picture of that event accordingly):

But dwelling on that stuff is a little morbid, even if it's kind of awe-inspiring.  So today, I'd like to look at some recent research that looks at how life recovered after the cataclysm -- discoveries that suggest the encouraging idea that even with a catastrophe, life can bounce back amazingly quickly.

A few years ago, Ian Miller and Tyler Lyson of the Denver Museum of Nature and Science were involved in a fossil dig in Corral Bluffs, Colorado, and made a rather astonishing discovery.  Initially the area seemed to be rather fossil-poor, but it had a great many concretions (roughly spherical blobs of cemented sediment).  When Miller and Lyson split one of these open, they found it was full of skeletal remains.

It turns out Corral Bluffs represent sedimentary layers of rock deposited immediately after the collision, so it provides an incredibly detailed record of the years following.  Large animals and flowering plants (especially trees) were hit the hardest by the extinction; despite the prevailing wisdom that "dinosaurs died and mammals didn't," the more accurate statement is "big species were much more likely to die than little ones."  The bottleneck, in fact, seems to have taken out all the mammals larger than your average rat.  (Miller and Lyson found no evidence of mammals larger than six hundred grams that survived the extinction.)  Miller, who is a paleobotanist, concentrated not on the animal remains but the plants -- especially the 37,000 pollen grains he found fossilized in the sediment layers.  And from this, a picture began to emerge of what things were like in the years following the collision, which was described this week in a fascinating paper in Science.

The largest group of plants to come through the bottleneck were ferns, which thrive in disturbed areas and have spores that are pretty damage-resistant.  Unfortunately for the animals, fern leaves and roots are rather low in nutrients, so for a while, body sizes remained small because there simply wasn't enough food around to support big, or even medium-sized, herbivores.  But within a few thousand years -- a flash, evolutionarily speaking -- Fern World was replaced by Palm World, as proto-monocots (the group that contains not only palms, but grasses, lilies, orchids, irises, and a variety of other familiar plant families) evolved to be more robust.  Palms have oily fruit that are high in sugar, and there's a commensurate jump in mammalian body size, with species showing up that weighed five kilograms.

Palms were superseded by the ancestors of today's walnuts and hickories a hundred or so thousand years after that, and in "Pecan Pie World" (as Miller and Lyson call this era), and the higher nutritional quality of those seeds fueled another jump in body size, with the largest ones reaching thirty kilograms (the size of a large dog).  And after seven hundred thousand years, legumes diversified, and the high protein content of these species triggered another growth spurt, topping out at fifty kilograms -- a hundred times larger than the survivors of the collision, in less than a million years.

Nota bene: the growth in size wasn't done yet.  The Oligocene Epoch, from 34 to 23 million years ago, saw the largest land mammals that have ever existed, including the enormous Baluchitherium, a behemoth that could have converted an African elephant into an African elephant pancake:

[Image licensed under the Creative Commons Waqas-anees2014, Baluchitherium, The Largest Land mammal at Pakistan Museum of Natural History (PMNH), CC BY-SA 3.0]

The Miller and Lyson study offers us a message that is simultaneously reassuring and terrifying.  First, the human-caused "Sixth Extinction" that we are almost certainly undergoing as we speak is not going to eliminate life on Earth, and the species that survive will quickly spring back and diversify once we stop doing whatever we can to make the planet uninhabitable.  But the cautionary tale is that no matter what, it won't be what we had.  The diversity of flora and fauna that existed before the Chicxulub Collision was gone forever, and even though "life found a way" (to borrow a phrase from Jurassic Park), what evolved afterward was dramatically different than what was lost.  And, to put not too fine a point on it, the years immediately following the bottleneck were pretty freakin' horrible for all concerned, with an entire planet laid waste, and the animals that weren't directly killed by the impact itself largely facing habitat loss and rampant starvation.

So we shouldn't be so quick to adopt the Pollyanna-ish "it'll all be fine, nature is resilient" attitude toward our current fossil-fuel-crazy, pollution-blind willfully ignorant behavior.  If anything, we should recognize how fragile it all is -- and how, if we push too hard, we're likely to see a collapse of catastrophic proportions.  While we can pretty much count on evolution eventually producing a whole new set of what Darwin called "endless forms most beautiful and most wonderful," there's more than a passing chance that we won't be around to see them.

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In keeping with Monday's post, this week's Skeptophilia book recommendation is about one of the most enigmatic figures in mathematics; the Indian prodigy Srinivasa Ramanujan.  Ramanujan was remarkable not only for his adeptness in handling numbers, but for his insight; one of his most famous moments was the discovery of "taxicab numbers" (I'll leave you to read the book to find out why they're called that), which are numbers that are expressible as the sum of two cubes, two different ways.

For example, 1,729 is the sum of 1 cubed and 12 cubed; it's also the sum of 9 cubed and 10 cubed.

What's fascinating about Ramanujan is that when he discovered this, it just leapt out at him.  He looked at 1,729 and immediately recognized that it had this odd property.  When he shared it with a friend, he was kind of amazed that the friend didn't jump to the same realization.

"How did you know that?" the friend asked.

Ramanujan shrugged.  "It was obvious."

The Man Who Knew Infinity by Robert Kanigel is the story of Ramanujan, whose life ended from tuberculosis at the young age of 32.  It's a brilliant, intriguing, and deeply perplexing book, looking at the mind of a savant -- someone who is so much better than most of us at a particular subject that it's hard even to conceive.  But Kanigel doesn't just hold up Ramanujan as some kind of odd specimen; he looks at the human side of a man whose phenomenal abilities put him in a class by himself.

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

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!]