Wipeout

252 million years ago, the Earth was hit by a confluence of Very Unfortunate Events.

First, most of the large continental land masses locked up into a single supercontinent, Pangaea.  This had multiple effects, including alterations of oceanic currents, massive desertification, and the collapse of the convection cells powering seafloor spreading at mid-ocean ridges.  The latter caused a drastic lowering of sea level and exposure of continental shelves, reducing habitat for marine species that live in shallow water (which is most of them).

Second, the tinder box that had formed in the Carboniferous Period -- enormous deposits of coal, oil, and limestone produced when the Earth was basically one giant greenhouse -- found its lit match when the Siberian Traps erupted.  This is one of the largest volcanic events known, and produced an almost unimaginable four million cubic kilometers of basaltic lava.  This ripped through all that coal and carbonate rock, releasing catastrophic amounts of carbon dioxide and sulfur dioxide into the atmosphere.  The portion of the excess absorbed into the ocean caused acidification, killing any marine animal with carbonate shells or skeletons.  The resulting temperature rise caused worldwide oceanic anoxia.  It very likely also triggered the unraveling of unstable methane clathrate deposits on the seafloor, releasing gaseous methane and further boosting the temperature.

If that weren't enough, right around this time the Araguainha Impactor hit what is now Brazil.  The spot where it struck was at the time mostly composed of another gift from the Carboniferous -- oil shale.  This was flash-incinerated, releasing yet more carbon dioxide.

The result: the extinction of between 80% and 95% of the species on Earth, depending on how you count them and who you ask.  

What there's no doubt of, though, is that it was devastating.  It's the closest the Earth has come to undergoing a complete wipeout.  Entire taxa went extinct, including eurypterids (sea scorpions), trilobites, blastoids, tabulate and rugose corals, and acanthoid fish; 99% of radiolarian species vanished, as well as 98% of gastropods and 97% of ammonites and foraminiferans.  The entire food web collapsed.

Afterward, the Earth was an overheated, sulfur-smelling, hypoxic, largely lifeless wasteland.

And yet, somehow, it recovered.  How exactly the Earth's living things made it through the largest bottleneck ever is the subject of a paper last week in the Geological Society of America Bulletin, authored by a team from University College Cork, the University of Connecticut, and the Natural History Museum of Vienna.  And what it found was that the bounce-back didn't happen all at once.  It was far from a linear progression toward rebuilding the biosphere -- there were further shifts and setbacks over several million years as life "found a way."

The team focused mainly on the plants, given that they're the base of the food web.  Some of the first recolonizers were conifers, but they suffered a reversal not even a million years after the main pulse of extinctions with the Smithian-Spathian Boundary Event, a further spike in global temperature that ultimately saw sea surface temperatures of 40 C (104 F), but which was then followed by an unexplained and equally rapid drop.  The wild pendulum swings in temperature caused the collapse of the resurgent coniferous forests; ultimately they were replaced by seed ferns and club mosses (the latter were larger than the ones we have today, but not as big as the enormous Lepidodendrons that were around during the Carboniferous).  

An early Triassic seed fern, Lepidopteris [Image licensed under the Creative Commons Vivi Vajd, Stephen McLoughlin, Sam M. Slater, Ola Gustafsson, Allan G. Rasmusson, Lepidopteris life restoration, CC BY 4.0]

Eventually the climate stabilized, but any way you spin it, the Early Triassic Period was a horrible time to be alive.  It was largely hot and dry, but then -- with startling rapidity -- terrestrial biomes were swamped during the weird Carnian Pluvial Episode, a two-million-year-long thunderstorm which I wrote about not long ago.  Then, at the end of the Triassic, there was yet another massive extinction, this one probably caused by the volcanism from the Central Atlantic Magmatic Province (which would ultimately open the Atlantic Ocean).  Things had largely settled down by the beginning of the Jurassic Period, at which point we were heading into a period of lush forests and (mostly) stable climate -- the long, glorious Age of Dinosaurs.

But as you know, even their salad days weren't destined to last forever.

It always strikes me, when I read papers like this one -- the colossal hubris and ignorance of people who think we can mess around with Earth's ecosystems with complete impunity.  They often shrug off any Cassandras with breezy lines like, "The Earth's climate has had swings in the past, and has always recovered."  And in one sense, sure, that's true.  Faced even with a catastrophic extinction like the Permian-Triassic, enough species made it through the bottleneck -- and the whipsawing that happened afterward, as the climate gradually restabilized -- to repopulate the Earth.

But keep in mind that a great many species didn't make it.  Most of them, in fact.  Then, at the end of the Cretaceous, the non-avian dinosaurs -- that had been the dominant group worldwide for two hundred times longer than humans have existed -- were completely eliminated.  Okay, life recovered once again, but even for the survivors, living through the event itself was no fun.

Oh, and allow me to put this whole grim story into perspective by mentioning the second paper that came out this week; a huge study out of James Cook University and the University of Adelaide showing unequivocally that tropical forests are dying off because of human-induced climate change -- that they're not adapting fast enough to cope with how quickly we're altering the climate.

We are the first species that has sufficient brainpower to understand how our actions affect the biosphere, and (perhaps) enough power to work toward mitigating them.  And instead, we're largely doing nothing, selling out the future in exchange for short-term expediency, a use-it-once-then-throw-it-away lifestyle, and enriching the coffers of corporate billionaires.  The current so-called administration's mottos with regards to the environment are "Deregulate everything," "Cut down more trees," and "Drill, baby, drill."

They, and all of us, should remember: sure, it's likely that whatever we do, in a million years there still will be plenty of life on Earth.  No matter the mistakes we make, the biosphere will survive.

But there is no guarantee that the survivors will include us.

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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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Deadly fireworks

I've always thought it would be amazingly cool to witness a supernova.

Imagine it.  Within a few hours, a dim, ordinary-looking star increases in luminosity until it outshines every other astronomical object in the sky except the Sun and Moon.  It's visible during the day and you can read by its light at night.  It's not a blink-and-you'll-miss-it phenomenon, either; the light from the massive explosion peaks rapidly but declines slowly.  Most supernovae will be visible for months, before dimming to near-invisibility, ending as neutron stars or black holes.

There are lots of candidates for what could be the next supernova, although don't get your hopes up; most of these fall into the "some time in the next million years" category.  Yeah, it could happen tomorrow, but I wouldn't put money on it.  Still, the list is sizable, and here are five of the best possibilities:

• Betelgeuse (720 light years away, in the constellation Orion).  This one got some serious press a few months ago because it suddenly started to decrease in brightness, and astronomers wondered if this was a prelude to an explosion.  What appears to have happened is that there was turbulence in the star's core that blew a cloud of dust from its surface, obscuring the star and making it appear to dim.  So we're still waiting for this red supergiant to explode, and probably will be for a while.
• IK Pegasi (154 light years away, in the constellation Pegasus).  IK Pegasi isn't well known because at an apparent magnitude of 6, it's not visible to the naked eye, but it bears mention as the nearest serious supernova candidate.  It's a double star -- a main-sequence star and a massive white dwarf orbiting a common center of mass.  As the main-sequence star evolves, it will become a red giant, with a radius large enough that its white dwarf companion will start suctioning matter from its surface.  When the white dwarf reaches what's called the Chandrasekhar Limit -- 1.4 solar masses -- it will explode cataclysmically as a Type 1a supernova.  This will not only be spectacular but potentially dangerous -- a topic we will revisit shortly.
• VY Canis Majoris (3,820 light years away, in the constellation Canis Major).  Another star not visible to the naked eye, VY Canis Majoris is a lot more spectacular than you'd think to look at it.  It's the largest star known, with a mass fifteen times that of the Sun, and a radius so large that if you put it where the Sun is, its surface would be about at the orbit of Jupiter (so we'd be inside the star).  This "hypergiant" is one of the most luminous stars in the Milky Way, and is only dim because it's so far away.  This one is certain to go supernova, probably some time in the next 100,000 years, and the remnants will collapse into a black hole.
• Eta Carinae (7,500 light years away, in the constellation Carina).  Eta Carinae is another huge star, with a radius twenty times that of the Sun, but what makes this one stand out is its bizarre behavior.  In 1837 it suddenly brightened to being one of the five brightest stars in the night sky, then over the next sixty years faded to the point that it was only visible in binoculars.  Detailed observations have shown that it blew out a huge cloud of material in "The Great Eruption," which is now the Homunculus Nebula.  It's a unique object, which makes it hard to predict its future behavior.  What seems certain is that it'll eventually explode, but there's no telling when that might occur.

The consensus amongst astronomers, however, is that the next likely supernova probably isn't on the list -- that it will be a previously-unknown white dwarf or an unremarkable-looking red giant.  We know so little about supernovas that it's impossible to predict them with any kind of accuracy.  And while this is an exciting prospect, we'd better hope that the next supernova isn't too close.

The Homunculus Nebula with Eta Carinae at the center [Image licensed under the Creative Commons ESA/Hubble, Cosmic Fireworks in Ultraviolet Eta Carinae Nebula, CC BY 4.0]

Not only do supernovas produce a lot of light, they generate a tremendous amount of radiation of other kinds, including cosmic rays.  A close supernova could produce enough cosmic rays to wipe out the ozone layer -- leading to a huge influx of ultraviolet light from the Sun, with devastating effects.

Scarily, this may have already happened in Earth's history.  One of the lesser-known mass extinctions occurred at the end of the Devonian Period, 359 million years ago.  Because it is poorly understood, and was dwarfed by the cataclysmic Permian-Triassic Extinction a little over a hundred million years later, it's not one you tend to read about in the paleontology-for-the-layperson books.  Even so, it was pretty significant, wiping out 19% of known families and 50% of known genera, including placoderms (armored fish), cystoids (a relative of the starfish), and graptolites (colonial animals not closely related to any living species).  Most striking were the collapse of reef-forming corals -- reefs didn't begin to form again on any significant scale until the Mesozoic Era, almost two hundred million years later -- and the near-complete wipeout of vertebrates.  The latter left no vertebrate species over a meter long (most of them were under ten centimeters), and again, it was millions of years before any kind of recovery took place.

Fortunately for us, it eventually did, because we're talking about our ancestors, here.

The cause of this catastrophe has been a matter of speculation, but a team led by Brian Fields, astrophysicist at the University of Illinois, may have found a smoking gun.  In a paper this week in Proceedings of the National Academy of Sciences, we find out that the most likely cause for the End-Devonian Extinction is a nearby supernova that caused the collapse of the ozone layer, leading to the Earth's surface being scorched by ultraviolet light.  This triggered a massive die-off of plants -- which had only recently colonized the land -- and worldwide anoxia.  

The result?  A mass extinction that hit just about every taxon known.

The idea that a supernova might have been to blame for the End-Devonian Extinction came from the presence of hundreds of thousands of plant spores in sedimentary rock layers that showed evidence of what appeared to be radiation damage.  This isn't conclusive, of course; the Fields et al. team is up front that this is only a working hypothesis.  What they'll be looking for next is isotopes of elements in those same rock layers that are only produced by bombardment with radiation, such as plutonium-244 and samarium-146.  "When you see green bananas in Illinois, you know they are fresh, and you know they did not grow here," Fields said, in an interview in Science Daily.  "Like bananas, Pu-244 and Sm-146 decay over time.  So if we find these radioisotopes on Earth today, we know they are fresh and not from here -- the green bananas of the isotope world -- and thus the smoking guns of a nearby supernova."

So as much as I'd love to witness a supernova in my lifetime, it'd be nice if it was one well outside of the terrifyingly-named "kill zone" (thought to be about 25 light years or so).  And chances are, there's nothing inside that radius we need to worry about.  If any of the known supernova candidates explode, we'll almost certainly be able to enjoy the fireworks from a safe distance.

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Fan of true crime stories?  This week's Skeptophilia book recommendation of the week is for you.

In The Poisoner's Handbook:Murder and the Birth of Forensic Medicine in Jazz Age New York, by Deborah Blum, you'll find out about how forensic science got off the ground -- through the efforts of two scientists, Charles Norris and Alexander Gettler, who took on the corruption-ridden law enforcement offices of Tammany Hall in order to stop people from literally getting away with murder.

In a book that reads more like a crime thriller than it does history, Blum takes us along with Norris and Gettler as they turned crime detection into a true science, resulting in hundreds of people being brought to justice for what would otherwise have been unsolved murders.  In Blum's hands, it's a fast, brilliant read -- if you're a fan of CSI, Forensics Files, and Bones, get a copy of The Poisoner's Handbook, you won't be able to put it down.

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

The tipping point

There's a common comment from climate change deniers that I'm sick unto death of, and it usually takes the form of something like "the Earth's climate has had ups and downs in the past, and life has gone along just fine."

First, it's the pure ignorance of this attitude that gets me.  If you did ten minutes' worth of research online, you'd find that a number of these "ups and downs" coincided with mass extinctions.  Life survived, yes, but dramatic losses in biodiversity and overall population numbers hardly constitutes "getting along just fine."  (In fact, the largest mass extinction ever -- the Permian-Triassic Extinction, which wiped out an estimated 96% of marine species and 65% of terrestrial species -- was coincident with a huge spike in temperature and atmospheric carbon dioxide, thought to have been triggered by a colossal volcanic eruption.)

But second, and honestly worse, is the blithe attitude that we can continue doing whatever we want to the environment and face no consequences whatsoever.  This raises entitlement to the level of an art form; apparently, we humans occupy such an exalted niche that no matter what we do, the rest of nature is magically going to make sure we not only survive, but thrive.

Even the most diehard deniers, however, are getting some serious hints that their determination to ignore science is not working out so well.  First of all, we have the fires in the Amazon, which have reached unprecedented levels in Brazil, with 74,000 acres burned to the ground already.  The cause is twofold -- the natural dry season, and the incomprehensible policy by Brazilian president Jair Bolsonaro of recommending large-scale slash-and-burn to "encourage agriculture."  The problem is larger in scale than just South America, however.  Environmental scientist Jonathan Foley explained why in an interview with Science News:

Some computer models... show a hypothetical scenario that when we clear rainforest, it starts to almost immediately warm up and dry out the atmosphere nearby.  When we stand in a forest, it feels cool and moist.  But when you clear-cut large areas of the forest, the air right around you gets hotter and drier, and it affects even rainfall patterns.  The worry is if you start clear-cutting more of the Amazon, in theory, a tipping point could be reached where the rest of the forest dries out, too. 

If that happens, the idea is that the Amazon could flip suddenly from being a rainforest to being a dry savanna-like ecosystem.  We’re not absolutely certain about it, but even that theoretical possibility is kind of terrifying...  Globally, about 10 to 15 percent of our CO2 emissions comes from deforestation.  If this is going back up again in Brazil, that’s going to make climate change even worse.

The only amendment that needs to be made to Foley's statement is his use of the word "if" in the last sentence.

Smoke from the 2019 Amazonian wildfires [Image is in the Public Domain, courtesy of NASA]

The other piece of alarming information this week comes from some research done at Stockholm University that firmed up a link between the salinity of the North Atlantic and climate throughout the world.  The team, made up of David K. Hutchinson, Helen K. Coxall, Matt OʹRegan, Johan Nilsson, Rodrigo Caballero, and Agatha M. de Boer, were studying the Eocene-Oligocene Transition (EOT), which occurred 34 million years ago and involved a shift from a "hothouse" to "icehouse" climate.  

The authors write:

The Eocene–Oligocene transition (EOT), ~34 Ma ago, marked a major shift in global climate towards colder and drier conditions and the formation of the first Antarctic ice sheets.  A gradual decrease in CO2 is thought to be the primary driver of the transition, causing long-term cooling and increasing seasonality through the Eocene, culminating in the glaciation of Antarctica.  Deep water circulation proxies suggest that the EOT, including the preceding 1 Myr, also marked either the onset or strengthening of an Atlantic meridional overturning circulation (AMOC).

Catch that?  An event occurring the North Atlantic is the probable trigger for the formation of the Antarctic Ice Sheet, and a radical change in Earth's climate -- and, unsurprisingly, a massive extinction that wiped out 20% of the Earth's species (large mammals were the hardest hit).

What Hutchinson and his team showed is that the likely cause of this transition was the closing of a oceanic channel between the Arctic Ocean and the North Atlantic.  The Arctic Ocean at that time had very low salinity (something the team demonstrated using the species of algae that show up in the fossil record from that time and place).  As long as the channel was open, fresh water flooded into the North Atlantic, keeping the salinity of the surface water low.  When the channel closed due to tectonic movement, the salinity of the surface of the North Atlantic spiked.  Saline water is more dense than fresh water, so this surface water began to sink, kicking off the "North Atlantic Thermohaline Circulation" and (more germane to our discussion here) drawing down dissolved carbon dioxide by the metric ton.

The result: a drastic drop in temperature, Antarctica becoming an ice-covered wasteland, and a mass extinction worldwide.

How anyone can read this and not be freaking out over the spike in carbon dioxide we've seen in the last hundred years -- that appears to be the fastest carbon dioxide concentration change anywhere in the geological record -- is beyond me.  There's no doubt that there's a tipping point, as the Eocene-Oligocene Transition shows.  The only question is where that tipping point is -- and whether we've already passed it.

What's driving it all is money.  Altering our lifestyle, protecting the rain forests, and divesting ourselves from fossil fuels all require that we make sacrifices ourselves, but more importantly, that we end the chokehold the fossil fuels industry has on our elected officials.  Of course the politicians don't want anyone to understand and accept climate science, because that would mean cutting off one of their biggest sources of donations -- the petrochemical industry.

It is fitting to end with a quote from Upton Sinclair: "It is difficult to get a man to understand something, when his salary depends upon his not understanding it."  The problem is, here what we're jeopardizing is not simply someone's salary, but the long-term habitability of the Earth.

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This week's Skeptophilia book recommendation is about a subject near and dear to my heart; the possibility of intelligent extraterrestrial life.  In The Three-Body Problem, Chinese science fiction writer Cixin Liu takes an interesting angle on this question; if intelligent life were discovered in the universe -- maybe if it even gave us a visit -- how would humans react?

Liu examines the impact of finding we're not alone in the cosmos from political, social, and religious perspectives, and doesn't engage in any pollyanna-ish assumptions that we'll all be hunky-dory and ascend to the next plane of existence.  What he does think might happen, though, makes for fascinating reading, and leaves you pondering our place in the universe for days after you turn over the last page.

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

A bolt from the blue

Two weeks ago, I wrote about a surprising fossil find in China showing that insects had rebounded after the horrific Permian-Triassic Extinction, 252 million years ago, with amazing speed considering the scale of the extinction and how slowly evolution generally goes.  An extinction opens up hundreds or thousands of ecological niches, which increases the selective pressure on the survivors to occupy them and avoid competition with the others -- which insects did, par excellence, and have been doing ever since.

The cause of the "Great Dying" has been a subject of conjecture for as long as we've known about it.  Candidates include:

• The formation of the Siberian Traps, an unimaginably huge lava flow covering most of eastern Siberia.  (Its volume is estimated at four hundred million cubic kilometers.)  The eruption would have burned everything in its wake, pumping tons of carbon dioxide into the atmosphere, and it would have released huge amounts of sulfur dioxide -- not only a poison, but one of the most powerful greenhouse gases.  The result; massive global warming and a catastrophic change in ecosystems worldwide.
• The lockup of Pangaea.  The collision of smaller continents to form a supercontinent has a number of effects -- the eradication of coastline along the colliding margin, ecological changes from shifting ocean currents, and collapse of mid-ocean ridges (resulting in a huge drop in sea level) among them.
• A "methane burp."  This sounds innocuous, but really, really isn't.  There's a tremendous amount of methane locked up in the form of clathrates -- a network of water ice with methane trapped inside.  These "frozen methane hydrates" coat the entire deep ocean floor.  The stuff is stable under cold temperatures and high pressures, but if something disturbs them, they begin to come apart, releasing bubbles of methane gas.  The bubbles expand as they rise, displacing more and more water, and when they hit the surface it causes a tsunami, not to mention releasing tons of methane into the atmosphere, which is not only toxic, it's also a greenhouse gas.
• Bombardment by swarms of comets and/or meteorites.  The problem with confirming this hypothesis is that any geological evidence of meteorite collisions would be long since eroded away.  If the object(s) that impacted the Earth were metallic meteorites, it's possible that you could use the same technique Luis Alvarez pioneered to explain the Cretaceous Extinction, which wiped out most of the dinosaurs -- enrichment of a layer of sediment by dust that's high in metallic elements not found in large quantities elsewhere.  But if it was a comet (mostly ice) or a rocky meteorite, we might not see much in the way of evidence of the event.

We just got a new piece of the puzzle last week, from research that also took place in China at a rock outcropping called the Penglaitan Section.  This formation dates from just before and just after the Permian-Triassic Extinction, and has the advantage of being 27 meters thick -- the sediment was being deposited rapidly when it formed, which means that you can see fine gradations in composition and narrow down the time range for when things happened.  (By comparison, the previous formation used is only 30 centimeters thick.)

Part of the Penglaitan Section [Image by Shuzhong Shen]

And what Penglaitan tells us is rather alarming.  The Permian-Triassic Extinction, which wiped out 95% of life on Earth and dwarfed the more familiar Cretaceous Extinction, happened in a relative flash.  And it wasn't (or wasn't solely) caused by temperature rise; the main pulse of extinctions happened suddenly, without any warning, and occurred when the temperature had only started its upward trajectory.  There was a five-degree temperature increase that occurred at the same time as the extinctions, but a much larger increase followed that, after the vast majority of the extinctions had already taken place.

Right now, the leading hypothesis is that the eruption of the Siberian Traps is the most likely cause.  But that in itself is horrific; it means that this colossal outpouring of lava not only happened suddenly, it happened with no warning.  Immediately prior to the extinction event, life was doing just fine -- the biodiversity was high, and there were no minor die-offs to presage the big one that was coming.

"We thought we would see a gradual decline in the diversity of life forms or, for example, certain species that are known to be less resilient than others, we would expect them to die out early on, but we don’t see that, said Jahandar Ramezani, of MIT's Department of Earth, Atmospheric, and Planetary Sciences.  "We can say there was extensive volcanic activity before and after the extinction, which could have caused some environmental stress and ecologic instability.  But the global ecologic collapse came with a sudden blow, and we cannot see its smoking gun in the sediments that record extinction...  The key in this paper is the abruptness of the extinction.  Any hypothesis that says the extinction was caused by gradual environmental change during the late Permian — all those slow processes, we can rule out.  It looks like a sudden punch comes in, and we’re still trying to figure out what it meant and what exactly caused it."

So that's pretty scary.  The idea that something on this scale could strike with essentially no warning whatsoever makes me realize how precarious life is, and how easily the interconnections between ecosystems that keep everything going could be disrupted -- not to mention the scale of the destruction if that happens.

Anyone out there still wondering why I'm so alarmed at the rate at which we're pouring fossil-fuel-derived carbon dioxide into the atmosphere?

Anyhow, that's our cheery message for today.  Monkey around with the ecosystem, and you could kill 95% of life on Earth.  I mean, I don't think it's likely to happen day after tomorrow, or anything, but the fragility of it all should give you pause.

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This week's Skeptophilia book recommendation is a fun one.  If you've never read anything by Mary Roach, you don't know what you're missing.  She investigates various human phenomena -- eating, space travel, sex, death, and war being a few of the ones she's tackled -- and writes about them with an analytical lens and a fantastically light sense of humor.  This week, my recommendation is Spook, in which she looks at the idea of an afterlife, trying to find out if there's anything to it from a scientific perspective.  It's an engaging, and at times laugh-out-loud funny, read.

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

Science shorts

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

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

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

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

The authors write:

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

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

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

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

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

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

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

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

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

Feldman writes, in a press release to EurekAlert!:

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

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

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


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

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

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

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

The dark side

I love science, but sometimes scientists can be their own worst enemies.

The reason I say this is that scientists sometimes have a tendency to throw caution to the wind and engage in speculation, which then gets reported by the media as "scientific fact."  When said speculation turns out to be false, or is superseded by other models for which there is more evidence, laypeople get the wrong idea that scientists sit around all day making shit up, and when it turns out to be wrong, they just make more shit up, and on and on it goes.

So media bears a large share of the blame for this, as usual.  But that said, it would be nice if there was some way for scientists to identify in their academic papers when they're engaging in tentative hypothesis, and when they're elaborating on a well-established and rock-solid theoretical model.

Amongst the latter would be evolution and anthropogenic climate change.  Just had to throw that in there.

But as an example of the former, let's look at a paper by Michael Rampino, professor of biology at New York University, who recently published a paper in Monthly Notices of the Royal Astronomical Society proposing that the periodic mass extinctions that have occurred on Earth might be caused by the interaction between the Solar System and a thin layer of dark matter along the galactic plane.  Rampino writes:

A cycle in the range of 26–30 Myr has been reported in mass extinctions, and terrestrial impact cratering may exhibit a similar cycle of 31 ± 5 Myr. These cycles have been attributed to the Sun's vertical oscillations through the Galactic disc, estimated to take from ∼30 to 42 Myr between Galactic plane crossings. Near the Galactic mid-plane, the Solar system's Oort Cloud comets could be perturbed by Galactic tidal forces, and possibly a thin dark matter (DM) disc, which might produce periodic comet showers and extinctions on the Earth. Passage of the Earth through especially dense clumps of DM, composed of Weakly Interacting Massive Particles (WIMPs) in the Galactic plane, could also lead to heating in the core of the planet through capture and subsequent annihilation of DM particles. This new source of periodic heating in the Earth's interior might explain a similar ∼30 Myr periodicity observed in terrestrial geologic activity, which may also be involved in extinctions. These results suggest that cycles of geological and biological evolution on the Earth may be partly controlled by the rhythms of Galactic dynamics.

The difficulty, of course, is that dark matter is still yet to be detected, despite years of search.  We can observe that there's something out there that, from its gravitational effects, seems to make up most of the universe's mass.  But what it's made of, and what its properties are, are completely unknown.  "WIMPs" -- the Weakly Interacting Massive Particles Rampino references in his paper -- are one candidate for the constituents of dark matter.  But they, too, are yet to be confirmed to exist, despite multiple experiments designed to detect them at the Large Hadron Collider.

So Rampino is proposing that a 31 ± 5 million year mass extinction cycle (5 million years representing a 15% variability either way) links to a 30 to 42 million year galactic-plane-crossing cycle (which represents a 16% variability either way) via a mechanism connected to a type of matter we've never seen and whose properties can only be guessed at.

Map of the "dark matter halo" surrounding a galaxy [image courtesy of the Wikimedia Commons]

Now, don't get me wrong.  Thinking outside the box is the way great discoveries are made.  For example, it was Einstein's decision to throw away the "problem of the constancy of the speed of light" that led to the discovery of the Theory of Relativity.  Einstein's contemporaries had spent decades trying furiously to explain away the fact that in a vacuum, light seemed to move at the same speed in all reference frames, something that couldn't happen according to classical mechanics.  All sorts of wild ideas were proposed -- for example, a universal "ether" that permeated the universe, and through which light moved -- and one by one they were knocked down.

Einstein, however, decided to take the "problem of the constancy of the speed of light" and turn it into the "law of the constancy of the speed of light" and see what mathematical predictions came out of that assumption.  And then, run experiments to see if those predictions worked.  Lo: the Theory of Relativity, with its wild time dilation and Lorenz Contraction weirdness.

All of which is a long-winded way of saying that there's nothing wrong with speculation.  I just wish there was some way for scientists to differentiate between when they're proposing a speculative hypothesis and reporting on an experimentally-supported theory.

Maybe they should write speculative articles in "Comic Sans."  I dunno.

I say this because I'm seeing stories come up all over the place, just in the last couple of weeks, claiming that "dark matter killed the dinosaurs."  Which Rampino himself would admit is not justified at this time (note in the passage I quoted how many times he uses the words "could," "might," and "may").  And when someone else proposes a different mechanism to explain the periodicity of extinctions, it'll also get reported as fact, and laypeople will have further evidence that all scientists do is come up with wild tales all day long.

So I really should revise my initial statement.  It's not that scientists are their own worst enemies.  It's that popular media are the scientists' worst enemies.  That, and the fact that the public still doesn't really understand how science is done (look at the ongoing confusion about what the word "theory" means).

And given the fact that a significant proportion of the public still doesn't accept the findings of science that aren't speculative, the last thing we need is to sow more doubt in people's minds by misrepresenting the parts of science that are still only conjecture.