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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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!]

Haremageddon

A couple of days ago there was a story out of North Dakota that's been making the rounds of the "Weird News" departments of various news agencies.  It's about a housing development in Fargo that has been "swarmed" by "dozens of dog-sized jackrabbits." 

Fargo resident Kayla Straabe told and ABC News reporter, "Every day, I feel like the crazy rabbit lady chasing them out of the yard where they're having a heyday.  There's at least 40 to 50 everyday, and they're in our yards and by a children's park."

The city pest control department claims not to be able to do anything about them, "because they're wild animals."  This strikes me as pretty peculiar.  Aren't all pests wild animals?  I mean, it's not like people are usually bothered by infestations of hamsters, or anything.

Be that as it may, the pest control department wouldn't do anything, but suggested that Straabe and others poison the jackrabbits, which she doesn't want to do.  So at the moment, the jackrabbits are still swarming in Fargo.

Which is an unremarkable enough story, until you look at the comments section.

Yes, yes, I know, sane people should never look at the comments section.  But I was curious as to what people thought about the cause, and what steps they thought should be taken, for this "flock of jackrabbits," a phrase which made me picture flying bunnies.  (I looked it up, and the correct collective noun for jackrabbits is a "husk," which to me sounds even weirder.  I suggest calling them a "lope of jackrabbits," which is much more euphonious.)

Some of the comments were reasonable enough.  A bunch of them suggested turning the jackrabbits into stew.  A couple recommended, given that it's Fargo we're talking about, running the jackrabbits through a wood-chipper.  But then things got weird, because people started weighing in on where the jackrabbits had come from in the first place, and it went downhill thereafter.

Here are a few samples.  Spelling and grammar have been left unaltered so you can get the full effect.

The government doesn't want you to see what's really happening with animals going on the rampage and flocks of birds dying and the news writes articles like it's completely normal?  Wake up.  This is only the first signs. 

Its a mutation.  Rabbits this huge, its not normal.  We spray pesticides all over the place and now we're reaping what we sow. 

Rabbits is one thing, what if this had been wolves? 

They can carry rabbies and they let them near a playground?  Bring them to Washington DC and let them go there.  You'll see how fast they disappear, and you won't hear the liberal lame stream media crying about the poor bunnies. 

Before the anti gun crazies got in charge, we would have known what to do about them before it became a problem. 

Giant rabbits, another sign of the unnatural things this government is doing.  Genetic engineering experiments gone wrong, and no one wants to blow the whistle, instead this will become more common until one day it becomes too late to do anything about it and people start dying.

Okay, will you people please just calm the fuck down?

These aren't vicious giant mutant bunnies, they're regular old jackrabbits.  According to the Wikipedia page on jackrabbits, this species normally gets to be two feet long and up to six pounds, which is (as the article said) the "size of a small dog."  No mutations, genetic engineering, or other "unnatural things" necessary.

And the bunnies haven't "gone on the rampage," they don't seem to be carrying "rabbies," and allowing people to run around shooting rabbits near a playground would create a whole different set of problems, you know?

So fer cryin' in the sink, let's take a deep breath, and relax.  This is not the Killer Rabbit of Caer Bannog we're talking about here.

Chances are, the jackrabbits have been driven into residential areas because it's winter and the foraging out in the wild is pretty slim, so they're going for decorative plantings in people's yards, which are more accessible through the snow.  The same thing happens in our area, but with white-tailed deer.  The deer, however, are kind of a nuisance year-round.  In some areas they make it impossible to have a garden unless you surround it by six-foot-high fence topped by razor-wire, and the number of car-deer collisions in upstate New York is astronomical.

On the other hand... maybe the deer are part of this whole evil scheme.  Mutated genetically engineered deer, released by Monsanto, so that we can't grow our own vegetables, and will be forced to purchase genetically-modified crops from grocery stores.  Probably the auto-repair industry is in on it, too, making sure the deer are bred to be attracted to car headlights.

And... and... it all started with Disney.  Remember Bambi?  Making us feel sorry for the poor little deer whose mother was killed by hunters.  And guess who Bambi's best friend was?

Thumper.  *cue scary music*

I guess that's enough evidence isn't it?  I believe we now have what the lawyers would call a "hare-tight case."