Budleigh Salterton, on the south coast of Devon, sits above the most terrifying cliffs on Earth. They are not very high. Even if you do not want to stand under them, they are not very prone to collapse. The horror takes a different form. It’s in the story they tell. Because they capture the moment when life on Earth almost ended.
The sediments preserved in these rocks were laid down during the early Triassic period, just after the largest mass extinction in the history of multicellular life that brought the Permian period to an end 252 million years ago. About 90% of the species died and fish and quadrupedal animals became more or less extinct between 30 degrees north of the equator and 40 degrees south.
Most remarkably, while biological abundance (if not diversity) tends to recover from mass extinctions within a few hundred thousand years, our planet remained in this almost inanimate state for the following 5 million years. When you study these cliffs, you will see the precipice where we waver.
The lowest layer at the western end of the beach is a bed of rounded pebbles. These are the rocks washed away from the Triassic mountains by floods and deposited in large garbage dumps by temporary rivers. Since the forests and savannas that may have covered the mountains had died, there was nothing that held soil and underground together, so erosion is likely to have accelerated greatly.
At the top of the stone bed there is a rocky desert surface. The pebbles here have been sculpted by the wind at sharp angles and varnished with shiny oxides, suggesting that the surface has remained unchanged for a long time. Above it are towering Red Triassic dunes. Through a peculiarity of erosion, these soft deposits have been sculpted into depressions that look eerily like fangs and screaming skulls.
We now know that there were two main extinction pulses. The first, which began 252.1 million years ago, most affected life on land. It coincided with a series of massive volcanic eruptions in the region that is now known as the Siberian Traps. The second, more devastating phase, began about 200,000 years later. It almost completed the extinction of terrestrial life, as well as wiping out the vast majority of species in the ocean.
While we cannot yet be sure, 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 escalating cycle of collapse.
The second phase seems to have been driven by global warming. 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, into rocks rich in coal and other hydrocarbons. The heat from the magma (underground lava) boiled the hydrocarbons, releasing huge amounts of carbon dioxide and methane. In other words, although there were no people on the planet, this disaster seems to have been caused by the burning of fossil fuels.
Temperatures are thought to have risen by between 8C and 10C, although much of the second phase of extinction may have been caused by an initial increase of between 3C and 5C. The extra carbon dioxide also dissolved in the oceans, raising their acidity to a point where many species could no longer survive. The rise in temperature seems to have caused ocean currents to stop, through the same mechanism that now threatens the Atlantic Meridional Tipping Circulation, which drives the Gulf Stream.
As wildfires raged across the planet, burning the vegetation protecting its surface, ash and soil would have poured into the ocean, triggering eutrophication (an excess of nutrients). Combined with the high temperatures and stalled circulation, this starves the remaining life forms of oxygen.
A paper released as repression in September may explain why the recovery took so long. Because so many of the world’s rich ecosystems had been replaced by desert, plants struggled to reestablish themselves. Their total weight on Earth decreased by about two-thirds. During these 5 million years, no carbon deposits were formed, since there was not enough crop production to make peat bogs.
In other words, the natural processes that remove CO2 from the atmosphere and turn it into wood and soil or bury it as fossil carbon stalled. For 5 million years, the world was trapped in this greenhouse state. In the cliffs at the eastern end of the bay, you can see when conditions finally began to change, as the fossilized roots of semi-desert plants wind down through the ancient dunes.
The story the rocks tell is about planetary tipping points: Earth systems pushed past 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 major life forms: the monsters of the Permians were replaced almost everywhere by dwarf fauna.
Could it happen again? Two parallel and contradictory processes are at play. At climate summits, governments develop weak voluntary commitments to limit the production of greenhouse gases. At the same time, almost every state with significant fossil reserves – including the UK – intends to extract as much as they can. A report by Carbon Tracker shows that if all the world’s reserves of fossil fields are extracted, their burning would exceed the carbon budget that governments have agreed to seven times.
While there is less carbon in these reserves than the amount produced during the Permian-Triassic extinction, the compressed time scale could make this release just as deadly for life on Earth. The increase 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. Even now, we seem to be approaching a series of possible turning points, some of which could trigger cascading collapse.
Everything now depends on what process prevails: the sometimes well-intentioned, but always weak, attempts to limit the burning of fossil coal, or the ruthless determination – often on the part of the same governments – to extract (and therefore burn) as much of it as possible, giving profits from older industries precedence over life on Earth. At the climate summit this month in Egypt, a nation where protests are prohibited and the interests of the people must always shift to the interests of power, we will see how close to the cliff edge the world’s governments intend to take us.