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.

****************************************

The bottleneck

When I was young, I was very much attracted to stories where things worked out because they were fated to happen that way.

It explains why so many of my favorite books and movies back then were Hero's Journey stories -- The Lord of the Rings, The Chronicles of Prydain, A Wrinkle in Time, Star Wars.  The idea that there's a reason things happen -- that life isn't just chaotic -- is seductive.  (And, of course, it's a major theme in most religions; so many of them have some version of "God has a plan.")

Appealing as this is, my view now is more like the conclusion Brother Juniper comes to by the end of Thornton Wilder's brilliant and devastating novel The Bridge of San Luis Rey -- that either God's plan is so subtle the human mind can't fathom it, or else there is no plan.  In my sixty-two years on this planet, most of what I've seen is much less like some orderly pattern than it is like a giant pinball game.

This seems to be true not only in the realm of human affairs, but in the natural world as well.  There are overall guiding principles (such as evolution by natural selection), but much of what happens isn't destined, it's contingent.  Even such basic things as our bilaterally symmetric body plans with paired organs, and our having five digits on each appendage, seem to be the result of what amount to evolutionary accidents.  (Which is why, if we're ever lucky enough to contact alien life, it is extremely unlikely to be humanoid.)

Another chaotic factor is introduced by random geological and astronomical occurrences -- the eruption of the Siberian Traps, for example, that kicked off the cataclysmic Permian-Triassic Extinction, and the Chicxulub Meteorite collision that took out (amongst many other groups) the non-avian dinosaurs.  Each of those events radically altered the trajectory of life on Earth; what things would look like now, had either or both of these not occurred, can only be vaguely guessed at.

It's a little humbling to think of all of the different ways things could have happened.  Most of which, it must be said, would result in Homo sapiens never evolving.  And researchers have just identified one more near miss on nonexistence our species had -- a colossal genetic bottleneck around nine hundred thousand years ago, during which our entire ancestral population appears to have dwindled to around thirteen hundred breeding individuals.

[Image licensed under the Creative Commons Jerónimo Roure Pérez, Homo heidelbergensis. Museo de Prehistoria de Valencia, CC BY-SA 4.0]

Species like ourselves, that are slow to reach maturity, which have few offspring at a time and require lots of parental care -- ones that, in the parlance of ecological science, are called K-selected -- tend not to recover from events like this.  The precariousness of the situation is highlighted by evidence that the population didn't really bounce back for over a hundred thousand years.

We were teetering on the edge of oblivion for a long time.

Evidence for this bottleneck comes from two sources -- a drastic decrease in human remains in the fossil record, and strong genetic evidence that all modern humans today descend from an extremely restricted gene pool, a little less than a million years ago.  This event coincided with the onset of a period of glaciation, during which sea level dropped, ice coverage expanded from the polar regions, and there were widespread droughts.  These conditions destroyed all but a tiny remnant of the human population -- and those few survivors are the ancestors of all seven billion of us modern humans.

Populations this tiny are extremely vulnerable, and that they survived long enough to recover is downright astonishing.  "It’s an extraordinary length of time," said Chris Stringer, of the Natural History Museum of London, who was not involved in the study.  "It’s remarkable that we did get through at all.  For a population of that size, you just need one bad climate event, an epidemic, a volcanic eruption and you’re gone."

We made it through, though.  Somehow.  And I guess near-catastrophes like this don't really settle the issue of whether it was all Meant To Be.  You can just as well interpret our winding path from the origins of life four billion years ago, with all of the close calls and almost-wipeouts we survived, as coming from our being part of some Master Plan.  But to me, it seems more like the vagaries of a chaotic universe -- one where all of us, humans and non-human species alike, are walking a tightrope.  If you went back sixty-seven million years and looked around, you'd have seen no reason to believe that the dinosaurs would ever be anything but the dominant group on Earth, but in the blink of the eye geologically, they would all be gone.  It's a cautionary tale about our own fragility -- something we should take to heart, as we're the only species on Earth that has evolved the intelligence to see the long-term consequences of our own actions, and potentially, to forestall our own being toppled from our position of dominance.

****************************************

Roots of the problem

It's natural enough to think that humans are the only organisms that damage their own habitat.  We certainly seem to be doing a damn good job of it.  But there have been other times living things have sown the seeds of their own destruction.

One good example is the Great Oxidation Event -- sometimes, justifiably, nicknamed the "Oxygen Holocaust."  It occurred just over two billion years ago, and hinges on one rather surprising fact; oxygen is a highly reactive, toxic gas.

There's good evidence that aerobic respiration -- the set of biochemical reactions that allows us to burn the glucose in our food, and which provides us with the vast majority of the energy we use -- evolved first as a mechanism for detoxifying oxygen, and only afterward got co-opted into being an energy pathway.  The problem was that prior to the Great Oxidation Event, all of the organisms had been anaerobes, which are capable of releasing energy without oxygen.  To the vast majority of anaerobes, oxygen is a deadly poison.  That's why when there was a sudden, massive injection of oxygen into the Earth's atmosphere a couple of billions of years ago, the result was that just about every living thing on Earth died.

The tipping point came with the evolution of yet another energetic pathway: photosynthesis.  Photosynthesis was a tremendous innovation, as it allowed organisms to harness light energy instead of chemical energy, but it had one significant downside.  The first part of the reaction chain of photosynthesis breaks up water molecules and releases oxygen.  So when the first photosynthesizers evolved -- probably something like modern cyanobacteria -- oxygen gas began to pour into the oceans and atmosphere.

Something like 99% of life on Earth died.

The survivors fell into three groups: (1) the handful of organisms that had some early form of aerobic respiration as a detoxification pathway; (2) anaerobes that had a way of hiding from the oxygen, like today's methanogens that live in anaerobic mud; and (3) the photosynthesizers themselves.

From the organisms that survived that catastrophic bottleneck came every living thing we currently see around us.

So we're far from being the only organisms that cause ecological problems.  The reason the topic comes up, in fact, is because of another example I'd never heard of until I bumped into a paper in the Geological Society of North America Bulletin last week; the Devonian mass extinctions, which are one of the "Big Five" extinction events that have struck the Earth.  This particular series of cataclysms wiped out an estimated seventy percent of marine species, but it may have been triggered by the evolution of something that seems innocuous, even benevolent.

Tree roots.

Plants had only colonized the land during the previous period, the Silurian, enabled to do so by yet another innovation; the evolution of vascular tissue.  The internal plumbing vascular plants have (the xylem and phloem you probably remember from your biology classes) allow plants to move water farther and faster, so they were no longer so tied to living in ponds and lakes.  Plus, vascular tissue in many plants doubles as support tissue, so this facilitated growing taller (a significant advantage when you're competing with your near neighbors for light).

But if you're taller, you're also more likely to topple when it's windy.  So then there's selection for who's got the best support system.  The winners: plants with roots.

Devonian Forest by Eduard Riou (ca. 1872) [Image is in the Public Domain]

Like vascular tissue, roots are multi-purpose.  They not only provide support and anchoring, they're good at creating lots of absorptive surface area for water and nutrients.  (Some roots are also evolved to store starch -- carrots come to mind -- but that's an innovation that seems to have come much later.)  So now we have a competition between plants for who's got the best supports, and who can access nutrients from the soils the fastest.

Roots very quickly became good at twisting their way into rocks.  You've undoubtedly seen it; tree roots clinging to, and breaking up, rocks, asphalt, cement, pretty much any barrier they can get a foothold into.  When that happened, suddenly there's an erosive force breaking up bedrock and transporting nutrients (especially phosphorus) into plant tissue.  Phosphorus began to leach out of the rock into the soil, and when the plants died all the phosphorus in the tissue was released into rivers, streams, and lakes.

The result was a massive influx of nutrients into bodies of water.

Have you ever seen what happens when chemical fertilizers get into a pond?  It fosters algal blooms, and when the algae dies and decomposes, the oxygen levels plummet and the entire pond dies.

That's what happened during the late Devonian Period -- but planet-wide.

The huge reef-building rugose and tabulate corals and stromatoporid sponges were wiped out en masse.  Other groups, such as trilobites and brachiopods, which depended on the reefs for habitat and food, got knocked back hard as well.

All, the authors claim, because of a nifty innovation in the structure of land plants.

It's tempting to think that the environment is stable; we look around us and think things have always been this way, and will always be this way.  What more of us need to understand is that while the global ecosystem is resilient up to a point, there is always a tipping point.  The scary part is we can pass that point suddenly, without even realizing it.  Then before we're even aware of what's happened, the last chance to turn things around is gone.

The difference between what happened during the Great Oxidation Event and the Devonian Mass Extinctions, and what's happening now, is that back then there was no conscious awareness on the part of the organisms who created the problem and those that were affected.  Now, we have (or should have) the awareness to see what is happening, and enough knowledge to make some smart decisions and halt the self-destructive path we're on.

Let's hope that it's not too late.

****************************************

A terrestrial heartbeat

When I was an undergraduate at the University of Louisiana, I took a class called Introduction to Astronomy from a fellow named Daniel Whitmire.  Dr. Whitmire made a name for himself, along with a colleague named John Matese (whom I later took a class in Quantum Mechanics from), with something that's been nicknamed the "Planet X" hypothesis.  This isn't some crazy, Nibiru-is-headed-toward-Earth claim; Whitmire and Matese were looking at an apparent periodicity in mass extinctions, which they suggested could be the effects of a massive planet far beyond the orbit of Pluto, perhaps with an eccentric orbit, which every so often passes through a dense part of the Oort Cloud and sends comets and other debris hurtling in toward the inner Solar System.

Since the time I first heard about it (in around 1980), the Planet X hypothesis has lost currency.  There's been no evidence whatsoever of a massive planet outside the orbit of Pluto, and in any case, further study has indicated that the extinctions (1) don't really show that strong a periodicity, and (2) have been pretty well explained from phenomena other than collisions (other than, obviously, the Cretaceous-Tertiary extinction).

[Image is in the Public Domain courtesy of NASA]

I found out last week, though, that Whitmire and Matese may have been on to something after all.

A curious paper that recently appeared in Geoscience Frontiers suggests that focusing solely on the extinctions may have hidden an underlying periodicity.  In "A Pulse of the Earth: A 27.5-Myr [million year] underlying cycle in coordinated geological events over the last 260 Myr," Michael Rampino and Yuhong Zhu (of New York University) and Ken Caldeira (of the Carnegie Institution for Science) did some detailed statistical analysis (the mathematics of which is beyond me) on 89 different major geological events on Earth -- marine and non-marine extinctions, major ocean-anoxic events, continental flood-basalt eruptions, sea-level fluctuations, global pulses of intraplate magmatism -- and found that there are striking, 27.5 million year peaks that have yet to be explained.

What jumped out at me is that the analysis isn't just some vague, it-looks-like-it-might-be-a-pattern.  The software they used found that the periodicity has a 96% confidence -- i.e. there's only a 4% chance that it's just noise that happens to look like a rhythm.  This means that they're on to something.  What, exactly, they're on to remains to be seen; the natural inclination is to look for some kind of tectonic process that for some reason is on a really slow cycle, but they did note one other curious possibility:

On the other hand, the main period of about 30 Myr is close to the Solar System’s ~ 32 ± 3 Myr vertical oscillation about the mid-plane of the Galaxy.  In the Galactic plane region, increased cosmic-ray flux might lead to significant climatic changes, whereas encounters with concentrations of disk-dark matter might trigger comet showers from the Oort Cloud, as well as thermal and geophysical disturbances in the inner Earth.  We note that a 26 to 37 Myr cycle has been reported in the ages of terrestrial impact craters, using various statistical techniques and sets of crater ages potentially connecting the terrestrial and extraterrestrial cycles.

Of course, figuring out the mechanism that causes the pattern comes after establishing that the pattern itself is real.  As I pointed out in my post on the Ganzfeld Experiment a couple of weeks ago, developing a model to explain a phenomenon has to wait until you've shown that there's a phenomenon there to explain.

But a 96% confidence level is enough to indicate that there's some underlying mechanism at work here that's worth further study.  Something, apparently, is causing a strange, regular pulse of catastrophes.  (To put your minds at ease -- I know this was one of the first things I wondered -- the last peak the analysis found occurred 12.1 million years ago, so we've got another fifteen-odd million years to go before the next one.  That is, if we don't manufacture a cataclysm ourselves first.)

For now, all we have is an odd, unexplained pattern in geological upheavals.  It will be fascinating to see what refinements are put on the analysis -- and whether the scientists can find out what's actually going on.  Until then, we're left with a mystery -- a 27.5 million year terrestrial heartbeat.

**************************************

The catastrophe clock

The human brain is a pattern-seeking machine.

We are evolved to look for correlations, probably because those correlations can be awfully useful.  Our habit of noticing patterns and cycles allowed the ancient Egyptians to figure out the timing of the Nile floods, essential for agriculture in a place that was (and is) a desert.  The people of east Africa did the same sort of thing with the monsoons.  In cool climates, knowing when the growing season was likely to start and end was absolutely critical.

The problem is, this same pattern-seeking feature can trick us into seeing illusory patterns in what are, in essence, random data.  Astrology relies on this sort of thing; a particularly common example recently is the freakout people have when Mercury goes into retrograde (an apparent backward motion of Mercury as seen from Earth because of their relative motion; obviously, Mercury doesn't actually start moving backwards).  Supposedly the whole world goes haywire when Mercury starts its retrograde motion, but believing this requires ignoring the fact that (1) Mercury goes into retrograde three or four times a year, for three or four weeks at a stretch, and (2) the world is kind of haywire all the time.  There's no reason to believe that humanity is any loonier during Mercury retrograde than it is at any other time of the year.

Sometimes those illusory patterns can be oddly convincing.  I remember when I was a kid that much was made of the strange coincidence that since William Henry Harrison was elected President of the United States in 1840, every presidential winner in a "zero year" has died in office: Harrison (1840), Lincoln (1860), Garfield (1880), McKinley (1900), Harding (1920), and Kennedy (1960).  Then Reagan (1980) and G. W. Bush (2000) stubbornly refused to die, forcing True Believers to come up with some kind of nonsense about how it was a 120-year curse and expired after JFK's assassination, or something.  Mostly, though, they just retreated in disarray, because it was a peculiar coincidence, not an actual meaningful pattern.

Fortunately, scientists have statistical methods for determining when you're looking at an actual pattern (i.e., whatever is happening occurs with a true cyclicity) and when you're just seeing random fluctuations or scatter in the data.  This can sometimes uncover odd patterns that are clearly real, but result from some as-yet unknown cause -- such as the natural disaster "heartbeat" that was the subject of a paper in Geoscience Frontiers last week.

Geologists Michael Rampino and Yuhong Zhu (of New York University) and Ken Caldeira (of the Carnegie Institution for Science) analyzed the timing of various major geologic events over the past 260 million years -- continental flood basalt eruptions, changes in the direction of plate movement, oceanic anoxia, major glaciations and changes in sea level, and mid-plate volcanism, as well as events like mass extinctions.  And they found that there was a statistically significant cyclicity to those events -- they tend to cluster every 27.5 million years, and have done so for hundreds of millions of years.

Artist's impression of the moment of the Chicxulub Impact 66 million years ago [Image is in the Public Domain courtesy of NASA and artist Donald E. Davis]

But detecting a pattern is not the same as determining what's behind it.  There is no known geological or astronomical event that occurs on a 27.5 million year cycle that might be the underlying cause of the periodic nature of catastrophes.  The authors throw out a few suggestions -- that it could be due to the motion of the Solar System relative to the rest of the Milky Way (oscillating above and below the plane of the galaxy, perhaps?), a thus-far unknown phenomenon originating in the motion of magma in the Earth's mantle, or the gravitational disturbance of the Oort Cloud by a massive, extremely distant planet orbiting the Sun.  (This latter idea has been around for a while; my college astronomy professor, Daniel Whitmire, was one of the first to treat it seriously, and he and his colleague John Matese wrote one of the first scholarly papers about the "Planet X" hypothesis.  But don't even start with me about Nibiru and the Annunaki, because I don't want to hear it.)

The upshot of it is we don't know.  But if you were worried, we're only about 7.5 million years past the last peak, so we have another twenty million or so years to go before the next one.  As optimistic as I am about my longevity, I seriously doubt I'll be around to see it.  The catastrophe clock has a lot of ticks left until the alarm goes off.

Which is a good thing.  As interesting as they are, flood basalt eruptions and oceanic anoxia and the rest are not events that would be fun to witness first-hand.

********************************************

Why do we have emotions?

It's a tougher question than it appears at first.  Emotions like joy and camaraderie can certainly act to strengthen social bonds; fear can warn us away from dangerous situations.  But how often do they get in the way?  The gray emotional vacuum of depression, the overwhelming distress of anxiety and panic disorder, and the unreasoning terror of phobias can be debilitating enough to prevent anything like normal day-to-day functioning.

In Projections: A Story of Human Emotions by Stanford University professor of bioengineering and psychiatry Karl Deisseroth, we take a look at case studies of emotions gone awry -- in Deisseroth's words, "using the broken to illuminate the unbroken."  His deeply empathetic and utterly fascinating account takes the reader through what can go wrong in our emotional systems, and the most recent, cutting-edge research in how the neurological underpinnings of our brains create our emotional world.

It is brilliant reading for anyone wanting to know more about where our feelings come from, and who seek to follow the ancient Greek maxim of γνῶθι σεαυτόν -- "know thyself."