Is this mass extinction a dark mirror to our future?
Burning fossil fuels may have driven the extinction of almost all life on Earth two hundred and fifty million years ago
It’s an unassuming place for an apocalypse. A quarry. There are no flashes of lightning, no peals of thunder, burning sconces, or horned, multi-eyed creatures. But the rocks in this quarry read like the Book of Revelation. The messengers delivering the grim story are equally unassuming. Geologists. They’re unlikely angels, typically a pretty light-hearted bunch, scruffy and bearded: the women not so much.
Picture our two geologists sitting in the dirt, hammers in hand. They are chipping out pieces of rock, placing them carefully in plastic bags, like treasure, labelling each with the number of the layer from which it came. Bed 23, Bed 24. A piece here shows the radiating, wing-like shell of a brachiopod, there a cluster of spiralled ammonites. These ancient, fossilized sea creatures are scattered throughout the rubble. But above Bed 25 they’re gone. Above Bed 25 the rocks are grey and barren. No creatures call back through the thousands of millennia from those silent years in Bed 26, 27, 28. Bed 25 records the Permian mass extinction, two hundred and fifty two million years ago, when ninety six percent of all life on Earth died.
Geologists have long known about the Permian mass extinction. But now they have new evidence that most life on Earth died remarkably quickly and of what, ultimately, tipped life into the abyss. Their conclusions cast a dark shadow on the future.
Exactly why the Permian mass extinction happened has long been debated, but most researchers agree that — like the perfect storm — it was a combination of many bad things, all happening at the same time. Take your worst day and multiply it by ten million. First, gradual environmental change made life more difficult. Food was hard to find. Then a series of massive volcanic eruptions released greenhouse gases into the atmosphere and it became hot, everywhere. About eight degrees hotter. The Earth — even the tropics — dried out, wildfires raged, forests burned. Like a sponge, the ocean soaked up all the extra carbon dioxide in the atmosphere, making the water acidic and toxic to all but the toughest creatures. Now life was really difficult. And somewhere in the midst of this hideous juxtaposition of worst days ever, something very bad happened. A tough existence became, literally, a cataclysm.
What was that very bad something that happened? Now, researchers have found sniffs of actual smoke in the rocks, drifting back to us through the eons, and forming a dark image of, not just that distant past, but perhaps — even probably —the future.
But first, let’s look at the timing. New research from China shows that the Permian mass extinction happened remarkably fast. This wasn’t easy to figure out: looking at ancient layers of rock, it can be difficult to say whether a few thousand or a few million years passed from one rock layer to the next. The layers are often thin, sporadically deposited sediments. It’s like a book with many pages torn out. Were there ten pages between each page that is preserved, or fifty? That’s where dating rocks comes in. A tiny mineral called zircon, in the ash from volcanoes, contains a small amount of uranium, which — over time — breaks down and becomes lead. By measuring the amount of uranium and lead in the zircon, we know exactly how old it is, and therefore we know when the volcano erupted. So we can measure the ages of ash layers above and below the extinction layer. But this still leaves us with a problem. If we have pages (or layers) ten to twenty and thirty to fifty, we know that the mass extinction happened between pages twenty and thirty, but we still don’t know whether it was on page twenty-one or page twenty-nine.
But this year, a breakthrough. In Penglaitan, South China, researchers found rocks with many thick sedimentary layers and many ash layers that were deposited before, during, and after the Permian mass extinction. Now they could date every bed and find out exactly how long it took for everything to die. The startling, horrific, result was that the extinction happened in 31,000 ± 31,000 years. It’s horrific because it shows that almost all life on Earth was wiped out, not in millions, but in thousands, or possibly even hundreds of years. Instead of thinking about this long gone event in geological time — millions of years, which are difficult to imagine — it’s much more akin to thinking of it as a brief period, or moment, in time. It’s more like referring to the 80s, or last Tuesday.
What worries researchers now, is that these thin layers of rock, this window into the past, is not a window, but a mirror. The Permian mass extinction event was the largest of five mass extinctions that rocked life on Earth. We are now in the midst of the sixth.
A sixth mass extinction? Could this really be true? It is true that we’ve seen — even caused — species extinctions. But species come and go all the time. If they didn’t, we might all still be jellyfish. That’s evolution. And did we need all those animals? What was the deal with dodos anyway? They couldn’t fly. They weren’t even very fast walkers. And quaggas? Yes, we killed them all, but they were only half a zebra in the first place. Do we need half a zebra? And giant beavers? Surely they were asking for it. But, looking closely, you have to admit that the list does go on a bit: North American megafauna, mammoths, all those weird Australian animals, really a LOT of birds and frogs. And I like frogs.
So yes, although species extinctions happen as part of the natural order of things, the difference in a mass extinction event is that the rate of extinction is much higher than normal. It is widely accepted that the current rate of species extinction is drastically higher than normal, unprecedented in human history, and unusual in Earth history. For example, while about five hundred vertebrate species died out in the past one hundred years, normally it would take thousands of years, or more, for those species to disappear. And that’s just vertebrates. Let’s say, accounting for all life on Earth, that there are about two species extinctions per year, which is probably a significant underestimate. Given that there are about 8.7 million species on Earth, and assuming no acceleration in extinction rate as life is progressively wiped out, in less than four and a half million years there would be no life on Earth. But, in terms of the extinctions we’re now seeing, that’s a best case scenario.
When we’re thinking about mass extinction, it’s not just the extinction of species that should concern us. Being in the midst of a mass extinction, many species under threat are not yet extinct, but are suffering dramatic declines in geographic range and population. Indeed, researchers from Universidad Nacional Autónoma de México and Stanford University argue that population losses should be ringing more alarm bells, referring to the “biological annihilation” of vertebrate species. For example, the latest Living Planet Report — a measure of the world’s biodiversity based on vertebrate populations — estimates that, worldwide, wildlife abundance has decreased by almost sixty percent in the past fifty years. This means that, if you’re fifty, there were more than twice as many animals alive on Earth when you were born than there are today. And these losses are not restricted to ‘at risk’ species, but spread across the spectrum of common to rare species, and across diverse habitats and regions. So while species extinctions are estimated to be hundreds, maybe thousands, of times higher than background, and expected to increase, population loss — a prelude to species extinction — is worse. It seems that our mass extinction is ticking along nicely.
Why is everything dying? Are we really so awful? Well, yes. Our impacts on biodiversity are not restricted to climate change, though it is a central theme. In fact, our impacts are far more broad and long-ranging; population growth, land use changes — particularly agriculture, urbanization, burning and deforestation — all leading to habitat loss, over-exploitation, pollution, toxification, islandisation, reduction in resources, translocation of invasive species, competition, and climate-related changes such as temperature changes and changed ocean and atmospheric chemistry. All of this leads to pressures on individuals, populations, and ecosystems.
But let’s get back to that line in the sand in Penglaitan. What was it, exactly, that fated almost all life to such a sudden demise? Geologists have known for a long time that massive volcanic eruptions preceded the Permian mass extinction. There had to be a connection. And certainly those eruptions delivered large amounts of greenhouse gases to the atmosphere, stressing late Permian ecosystems. But there are two big problems that researchers had been grappling with. One — the timing doesn’t quite work. The volcanic eruptions began about three hundred thousand years beforehand, so why did it take so long before everything died? Two — researchers can’t squeeze enough greenhouse gases out of the eruptions to produce the huge climatic changes that actually happened. So where did those greenhouse gases come from? This is where the story gets ugly, for us in particular. This year, Dr Benjamin Burger, a researcher from Utah State University, identified mercury and lead in the rocks formed during the mass extinction. Mercury and lead are not produced by volcanoes, but they are common by-products of burning coal. And Canadian researchers have found fly-ash in rocks formed immediately before the extinction: fly-ash is also formed by burning coal. That’s right. It turns out that it’s not just us burning coal. It’s happened before. And here’s where we get to that worst day ever times ten million scenario.
The picture, now emerging, is that huge volumes of magma produced by the volcanoes, infiltrated into, and ignited, massive subsurface coal deposits, releasing vast amounts of methane and carbon dioxide into the atmosphere. It would seem that it was this sudden, massive dump of greenhouse gases from burning fossil fuels that pushed the, already stressed, Permian ecosystem over the edge, driving extinction of almost all life on Earth within a few thousand years, or less. Suddenly, the parallels are stark.
Perhaps the great day of wrath is, indeed, upon us. Perhaps the riders are coming, bringing war, famine, pestilence, death. Will any of us be marked with that seal that protects us from the hunger, fire, bitter water, and scorching heat? Or will the seventh seal bring the same silence that marks Bed 25 and the barren rocks above it?
From inside the system, living within a mass extinction event, rather than after the fact, it’s difficult to see clearly. But the scale and nature of our impact has dark parallels with the end Permian mass extinction. Unlike the last five mass extinctions, the one we are experiencing now has the unique and dubious distinction of being driven — largely, if not entirely — by the actions of a single species. It would be exciting, if one were looking at it academically from the distant future, as geologists today are looking at the Permian mass extinction. But unfortunately, we’re not. Unfortunately, we’re looking at it from the present, seeing dramatic and accelerating extinctions of species, reduction in their ranges, populations, and resilience. And what we perhaps fail to remember is that we are also a species. While we continue our dramatic domination of the planet, we too will, ultimately, hit the same wall that other animals are already hitting. A hundred million years from now, should there be geologists of some future intelligent species on Earth, they will note our mass extinction — quite literally — as a line in the sand.