Photograph: Joana Kruse / Alamy
Budleigh Salterton, on the south coast of Devon, sits above the scariest cliffs on Earth. They are not particularly tall. Even if you don’t want to be under them, they’re not particularly prone to collapsing. Horror takes on another form. It is contained in the story they tell. Because they capture the moment when life on Earth has almost come to an end.
Sediments preserved in these reefs settled in the early Triassic, just after the largest mass extinction in the history of multicellular life that ended the Permian period 252 million years ago. About 90% of the species died and fish and quadrupeds were more or less exterminated between 30 degrees north of the equator and 40 degrees south.
More surprisingly, while biological abundance (if not diversity) tends to recover from mass extinctions within a few hundred thousand years, our planet remained in this nearly lifeless state for the next 5 million years. Studying these cliffs, you see the precipice on which we totter.
The lowest layer at the western end of the beach is a rounded pebble bed. These are the stones washed from the Triassic mountains by flash floods and deposited in large landfills by temporary rivers. Since the forests and savannas that could have covered the mountains were dead, there was nothing holding the soil and subsoil together, so erosion is likely to have accelerated considerably.
At the top of the cobblestone bed is a stony desert surface. The cobblestones here have been wind-sculpted in sharp angles and painted with glossy oxides, suggesting that the surface has remained unchanged for a long time. Above it rise red sand dunes from the Triassic period. Through an oddity of erosion, these soft deposits have been carved into hollows that look eerily similar to fanged and screaming skulls.
We now know that there were two major extinction impulses. The first, which began 252.1 million years ago, primarily affected life on land. It coincided with a series of massive volcanic eruptions in the region now known as the Siberian traps. The second, more devastating phase began about 200,000 years later. It has nearly completed the extinction of terrestrial life, as well as wiping out the vast majority of species in the sea.
While we can’t be sure yet, the first phase may have been triggered by acid rain, ozone depletion, and metal pollution caused by volcanic chemicals. As rainforests and other ecosystems were wiped out, more toxic compounds were released from exposed soils and rocks, creating an increasing cycle of collapse.
The second phase appears to have been driven by global warming. By 251.9 million years ago, so much solidified rock had accumulated on the surface of the Siberian traps that the lava could no longer escape. Instead it was forced to spread underground, along horizontal cracks, in rocks rich in coal and other hydrocarbons. The heat of the magma (underground lava) has cooked the hydrocarbons, releasing large quantities of carbon dioxide and methane. In other words, although there were no humans on the planet, this disaster appears to have been caused by the burning of fossil fuels.
Temperatures are believed to have risen between 8 ° C and 10 ° C, although much of the second extinction phase may have been caused by an initial increase of between 3 ° C and 5 ° C. The extra carbon dioxide also dissolved in the oceans, increasing their acidity to the point that many species could no longer survive. The rise in temperature appears to have stopped ocean currents, through the same mechanism that now threatens the southern Atlantic overturning circulation, which drives the Gulf Stream. As fires raged across the planet, incinerating vegetation and protecting its surface, ash and soil would spill into the sea, triggering eutrophication (an excess of nutrients). Combined with the high temperatures and blocked circulation, this has starved the remaining life forms of oxygen.
A paper released as a pre-press in September could explain why the recovery took so long. As so many of the world’s rich ecosystems had been replaced by the desert, plants struggled to recover. Their total weight on Earth has decreased by about two thirds. In these 5 million years, no coal deposits were formed, as there was not enough production of plants to build peat bogs. In other words, natural processes that remove CO2 from the atmosphere and turn it into wood and soil or bury it as fossil carbon freezes. For 5 million years, the world has been trapped in this greenhouse state. In the cliffs at the eastern end of the bay, you can see when conditions have finally started to change, as the fossilized roots of semi-desert plants meander through the ancient sand dunes.
The story told by the cliffs is of planetary tipping points: Earth systems have passed their critical thresholds, beyond which they collapsed into a new state of equilibrium, which could not be easily reversed. It was a world hostile to almost all great life forms: the Permian monsters were replaced almost everywhere by dwarf fauna.
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Could it happen again? Two parallel and contradictory processes are at stake. At the top on the climate, governments produce weak voluntary commitments to limit the production of greenhouse gases. At the same time, nearly all states with significant fossil reserves, including the UK, intend to mine as much as possible. A Carbon Tracker report shows that if all of the world’s fossil reservoirs were extracted, their combustion would exceed seven times the carbon budget that governments have agreed upon. While these reserves contain less carbon than the amount produced during the Permian-Triassic extinction, the compressed time scale could make this release just as deadly to life on Earth. The rise in atmospheric CO2 at the end of the Permian took about 75,000 years, but many of our fossil fuel reserves could be consumed over decades. It appears that we are already approaching a number of possible tipping points, some of which could trigger a cascade collapse.
It all now depends on which process prevails: the sometimes well-intentioned, but always feeble attempts to limit the burning of fossil carbon, or the ruthless determination – often by governments themselves – to extract (and then burn) as much as possible. , granting the profits of legacy industries priority over life on Earth. At this month’s climate summit in Egypt, a nation where protests are banned and the interests of the people must always yield to the interests of power, we will see how close to the precipice the world’s governments intend to take us.