by Riskin, Dan
Whenever you mention extinctions, people usually think of dinosaurs, but the funny thing about dinosaurs is that they didn’t actually go extinct. There was an event 65 million years ago, at a point in time that separates the Cretaceous period from the Paleogene period. That moment in geological time is called the Cretaceous-Paleogene boundary, or K-Pg boundary. It was then that almost all the dinosaurs disappeared, but a few did survive. In fact, their descendants live on to this day, and you see them all the time. Those descendants are the birds, and because all birds are direct descendants of the dinosaurs, birds, by definition, are also dinosaurs.XIX (Watch a chicken run and tell me it doesn’t look like a velociraptor from Jurassic Park.)
Because the dinosaurs didn’t go extinct, paleontologists are always careful to call the group that did die off at the K-Pg boundary the “non-avian dinosaurs.” That’s their way of saying “all the dinosaurs except the birds.”
The K-Pg extinction may have wiped out charismatic animals like Tyrannosaurs and Triceratops, but the non-avian dinosaurs weren’t the only ones that disappeared. Flying reptiles called pterosaurs did too (they weren’t technically dinosaurs), as did the big swimming reptiles that looked like Loch Ness monsters (also not dinosaurs) and a whole bunch of other plants and animals. In all, roughly 70 to 75 percent of all species on Earth disappeared.27
The evidence is very strong that the K-Pg extinction event began when a massive meteor smashed into what is now Mexico, right near Mérida, on the Yucatán Peninsula. How big was it? For context, think back to that fireball that lit up the sky over Chelyabinsk, Russia, in February 2013. That meteor was about fifty-five feet across28—big enough that when it burned up in the sky, it released a flash of light brighter than the sun and sent out a shock wave powerful enough to knock over building walls, shatter windows, and injure more than a thousand people. Millions of rocks of various sizes hurtle into our atmosphere each year, but the Chelyabinsk meteor is the biggest one Earth has seen in the past century.
The meteor that wiped out the non-avian dinosaurs? Oh, slightly bigger.
It left behind a crater about 125 miles in diameter, which means the asteroid itself was probably about 6 miles in diameter. Six miles! That makes it more than five hundred times wider than the Chelyabinsk meteor, and more than 200 million times heavier.29
Animals standing right under it would have been vaporized by the fireball when that impact occurred, and those nearby would have been killed by the wildfires and tidal waves that spread out from the impact site, but the global-scale problems came in the ensuing months. The dust kicked into the atmosphere by that impact would have blocked out sunlight, and since energy coming into the living world must be harnessed by plants from sunlight (as you’ll recall from the chapter on gluttony), this debris cut off the flow of energy not only to plants but also to all animals. By the time the dust settled, months or even years later, most of Earth’s species were dead.
Events like the asteroid at the K-Pg boundary are part of nature, as are the smaller-scale events we’ve seen in our lifetimes, like earthquakes, tsunamis, hurricanes, tornadoes, and blizzards. When natural disasters happen, animals die, and when the event is big enough, a whole species or multiple species can vanish. Those extinctions are an important factor in how life has evolved on our planet. For one thing, mammals were only able to become things like horses, bats, and apes because the non-avian dinosaurs were gone.30 If that asteroid hadn’t hit, if all that death hadn’t happened, humans wouldn’t exist. By the same token, humans will surely someday experience an extinction of our own. That’s just how nature rolls.
The mass extinction at the K-Pg boundary wasn’t the only one in Earth’s history. In fact, it wasn’t even the biggest. Before dinosaurs ever existed, an extinction event 251 million years ago killed 95 percent of all species on Earth. That mass extinction, between the Permian and Triassic periods, is (not surprisingly) called the Permo-Triassic boundary, or P-Tr boundary. Some people, however, just call it the Great Dying. Almost every single kind of plant, insect, fish, amphibian, and reptile disappeared, including some reptiles as big as bears. All that was left was a tiny sliver of the biodiversity that had existed before.
The P-Tr extinction seems to have been triggered by giant volcanoes in what is now Siberia. Volcanoes don’t sound that threatening, but we’re not talking about lava flowing down a hillside. We’re talking about massive fields of volcanoes that burped up enough lava that it ultimately covered an area of 1.6 million square miles—roughly half the area of the contiguous United States. The lava would have been bad for the animals right at the volcanoes, but the gases that came out wreaked havoc worldwide. They triggered a cascade of environmental changes that animals on land and in the oceans simply could not handle—poisonous gases, steep drops in aquatic oxygen levels, and runaway global warming with increases of around 11˚F (6˚C). To give you some idea of how bad it was, in some places the soil was completely wiped away, killing everything that had once lived there, except the molds and other fungi that could cling to the bare rock left behind. Despite the magnitude of that carnage, a few living things did manage to survive, and after a few million years, their descendants evolved to fill the roles of some of the creatures that had died. Some of those new creatures, for example, were the dinosaurs.31
The K-Pg and P-Tr extinctions are the best-known mass extinctions, because there are heaps of fossils from those events. But there’s one other extinction that most experts believe was even more catastrophic. It’s a little bit more mysterious than the others, though, because it happened so long ago that everything that lived was single-celled. And all the fossils of single-celled organisms look very similar, making it hard to tell exactly which species survived and which did not. But it’s an extinction with special relevance for us, because unlike the K-Pg and P-Tr extinctions, which were caused by meteors and volcanoes that you can’t really blame on anyone, that early extinction was caused by living things.
It happened 2.4 billion years ago, and it was devastating. Just about every form of life on Earth died, killed by a poisonous gas. That poisonous gas had only existed on Earth before in trace amounts, but suddenly it increased in concentration more than a thousandfold, wreaking death on land and in the seas. The gas was oxygen, and it came out of algae as a waste product from the new trick they’d just learned, photosynthesis. The name for that massive extinction is the Great Oxygenation Event.32
It might be hard to think of oxygen as a poisonous gas, but to many creatures it is. In fact, the word poisonous almost doesn’t do it justice. Oxygen is horrible, and to live in a world of it, you need an arsenal of molecular defenses at the ready.
Oxygen loves electrons and will rip them off anything it can get near. Iron rusts because oxygen rips the electrons out of it. When you see a piece of wood burn, you’re watching the oxygen all around it tear the electrons out of it, releasing energy as heat and light. (That’s why fires need oxygen.) When our bodies break down sugars, we’re using a complex molecular machinery to harness the energy that is released when the oxygen we breathe rips the electrons out of the sugars we’ve consumed.
Living things didn’t have that kind of molecular machinery 2.4 billion years ago, so when oxygen invaded their bodies, they were corroded alive. The oxygen was coming out of early algae that were just doing their best to survive and as a result ended up pumping oxygen out of their bodies. This had the consequence of changing the rules of life for the other creatures of Earth. Most organisms had been doing just fine breathing gases like methane, but after the Great Oxygenation Event, either they found a way to cope with oxygen or they died.XX
Today, oxygen makes up more than 20 percent of the atmosphere, and animals have adapted to use oxygen’s volatility to their advantage. You can get almost twenty times more energy out of oxygen than you could ever possibly get from methane, so looking back you could try to argue that the Great Oxygenation Event was a good thing. It’s not like Earth was getting things ready for us, thou
gh. Humans breathe oxygen because that’s what we evolved with. We’ve played with the cards we were dealt.XXI
The wrath of nature goes well beyond the pain and suffering of a person bitten by a rattlesnake. Time and time again, living things are swept off the face of the Earth before new forms of life grow again. All three of the extinctions I mention serve as reminders of the wrath inherent to nature, but they’re also good reminders that life carries on despite them. There’s nothing permanent about Sam or his DNA or any living thing on the planet. DNA churns away, making meat robots, and those meat robots do their best to survive, subject to the whim of fate. Sometimes the rules change suddenly, but that’s just how the cookie crumbles.
Like any other species before us that has enjoyed some time in the sun on this planet, our days here are numbered. There was nothing wrong with the methane-breathing cells that faced those first clouds of oxygen. They were just unlucky. The pterosaurs might well have survived through to today had it not been for a wayward asteroid. Humans are no different. A stroke of bad luck will one day put us out like a cigarette. In fact, that bad luck may well be our own brains, which have set to work causing nuclear meltdowns, wars, and rapid climate changes on a par with what has happened during other extinction events. We’ve wiped out many animals in the last century, including the Tasmanian wolf, the passenger pigeon, and the Caribbean monk seal. Perhaps you could say we are playing the role of the asteroid this time.
I find the fact that humans are causing animals around the world to face extinction overwhelmingly depressing, but I do get a sliver of solace knowing that no matter how badly we screw this world up, something new, and different, will thrive. Earth bounced back from those other disasters. We will never get the animals we’re killing back, but in 10 million years, the world just might look like nothing ever happened.
It’s fascinating how differently we humans treat the fate of our own DNA, depending on the time scale. We protect ourselves and our children at any cost, but when we think a few generations down the road, we’re barely willing to be inconvenienced. It makes sense. Our DNA has programmed us to live in the present—to protect those of our progeny that are on the Earth at the same time we are. Our DNA can’t think a century ahead to what climate change will do, or overfishing, or habitat loss. Besides, saving the environment would benefit other humans’ DNA as much as our own. Because that wouldn’t give our own DNA a selfish competitive advantage, it’s not really part of our DNA’s job description. Our instincts weren’t built to handle the kind of power our species now wields over the planet. Nature’s been playing rough with us for so long, maybe it’s no surprise that we’re being so rough with her now.
I certainly don’t want Sam to have to raise his own kids in a world without black rhinos, but it looks like that’s what’s going to happen.XXII However, I have the luxury of worrying about that because the odds are I’m not one of the parents who will lose a child to a venomous snake bite this year. I only get to think about long-term consequences because my DNA’s short-term needs are met. If we’re going to ask people around the world to preserve the plants and animals we think deserve to live here, we’re going to have to help those humans escape the wrath of nature first.
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I. We’ve known since the 1970s that killer whales fit into two groups: “resident” whales, which feed on fish, and “transient” whales, which eat marine mammals (Baird and Dill 1996). Recently, though, killer whales that feed on sharks out in the open ocean have been documented. It’s not yet known whether those whales form a third, separate group or whether they’re just a subset of one of the other two (Ford et al. 2011).
II. Once a pod of killer whales has killed a great big whale, they have way more food than they can eat right away. In Alaska, killer whales will sometimes store the giant’s carcass near a beach. The cold water acts like a refrigerator, and the killer whales can come back for leftovers repeatedly over the course of several days (Barrett-Lennard et al. 2011).
III. I was once told on a whale-watching tour that “killer whale” is no longer the accepted name for these animals, and that the term “orca” is preferred, to reflect the fact that wild killer whales/orcas don’t hunt humans. I think the name suits them beautifully. (Not everything has to be about humans.)
IV. The Portuguese man-of-war gets its name from the boatlike air-filled float that sits on the surface of the water, above the dangling tentacles (a man-of-war was a type of warship used in the sixteenth to nineteenth centuries). That float allows the jelly to be moved around by wind, in addition to ocean currents (Šuput 2009).
V. Obviously I don’t condone smoking, but if you’ve just been stung by a cone snail, an increased likelihood of lung cancer is the least of your problems.
VI. Only about 0.1 percent of those proteins have been analyzed well enough that we have any clue what they do (Lewis et al. 2012).
VII. An arachnologist (spider expert) named Norman Platnick at the American Museum of Natural History, in New York, keeps an online database of all the spiders that are known to science. Last time I checked, he had 44,032 species listed (Platnick 2013), but the list of spider species that haven’t been described yet may be four times that long (Vetter and Isbister 2008).
VIII. Specifically, the deadly spiders are the Australian funnel-web spiders (Atrax and Hadronyche), the South American armed spiders (also called banana spiders, Phoneutria), and the recluse spiders (Loxosceles) and widow spiders (Latrodectus) found across several continents (Isbister and Fan, 2011).
IX. Apparently, antivenin is the correct term for what should really be called an antivenom. I know. It drives me nuts too, but if you want to sound like you know what you’re talking about, you have to say “antivenin.”
X. The class Arachnida includes spiders (order Araneae), scorpions (order Scorpiones), mites and ticks (order Acari), and a bunch of other, less well-known eight-legged creatures. Personally, I’m very creeped out by tailless whip scorpions (order Amblypygi) and the so-called camel spiders (order Solifugae). I think it’s probably because the first time I ever encountered those animals I didn’t even know they existed, and because both of them have mouthparts that look like they were thought up by David Cronenberg.
XI. Fire ants aren’t actually native to the southern USA. They’re from South America but got introduced via cargo ship to Mobile, Alabama, in the 1930s. Today, fire ants span the southeastern USA and Puerto Rico, and there’s a very real possibility that their range will continue to spread until it covers the entire southern USA, right across from Florida to California.
XII. As a German colleague of mine once said outside a bat cave in Texas, right before she pulled her pants off in front of our whole lab group, “It is like hell!”
XIII. Last time I checked, there were 12,763 ant species known, but it’s likely at least that many are still out there waiting to be discovered. A running tally is kept by scientists at Ohio State University: http://osuc.biosci.ohio-state.edu/hymenoptera/tsa.sppcount?the_taxon=Formicidae.
XIV. I know that seems like a bit of a weird thing to think about, but it really does drive home just how many ants are out there (Fittkau and Klinge 1973).
XV. Indigenous tribes on the outskirts of Manaus, in the heart of the Amazon, make money by performing this ritual in front of tourists. Personally, I think tourists should have to perform the ritual instead (Botelho and Weigel 2011).
XVI. Dr. Schmidt isn’t some nut. He is a well-respected scientist, and I would argue that his willingness to experience those stings firsthand shows just how passionate he is about his subject of study. It’s a good thing he doesn’t study cone snails, though.
XVII. One of my closest friends during my PhD studies was a guy named Rulon who studied timber rattlesnakes in the wilds of upstate New York. When he would tell people about his research, they would often ask him “What are they good for?” So Rulon wrote a piece for Natural History magazine that answered that question beautifully. If you want a sense of what makes
those snakes such beautiful creatures, and want to see just how passionate a researcher can be about his research animals, I highly recommend that article (Clark 2005).
XVIII. My rattlesnake-expert friend Rulon once told me over beer that he thought dry bites might be the reason there are so many strange folk remedies for snake bites. After all, if only half of snake bites involve venom, then any remedy will appear to have saved you 50 percent of the time. That might explain some of the folk remedies that are out there, like sucking the bite hole, soaking the bite in kerosene, killing the snake and rubbing its body on the wound, or killing a chicken and wrapping its meat around the wound.
XIX. http://www.xkcd.com/1211/
XX. In those places on Earth that oxygen hasn’t reached, like hydrothermal vents at the bottom of the ocean, inside geysers, or deep within some caves, many of those non-oxygen-breathing organisms still thrive. That’s why you often hear people say that living things from those places might give insights into what life might be like on other planets where oxygen doesn’t exist.
XXI. There’s something beautiful to me about the fact that when a yoga class takes a deep breath of that clean, rejuvenating oxygen, they’re taking in a gas that wiped out almost every living thing on Earth. The world doesn’t provide for living things; it’s the living things that have evolved to thrive on whatever happens to be around.
XXII. The number of black rhinos killed in 2012 was 668, almost 15 percent of the entire population. Compare that with 2007, when only 13 were poached, and you get a sense of how rapidly things have deteriorated for those animals in the last decade (Biggs et al. 2013).
