[A] We now know that there were two main pulses of extinction. The first, which began 252.1m years ago, mostly affected life on land. The second, more devastating phase, started about 200,000 years later. Though we cannot yet be sure, the first phase might 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.

[B] Budleigh Salterton, on the south coast of Devon, sits above the most frightening cliffs on Earth. They are not particularly high. The horror takes another form. For they capture the moment at which life on Earth almost came to an end.

[C] A paper released might explain why recovery took so long. Because so many of the world’s rich ecosystems had been replaced by desert, plants struggled to re-establish themselves. Their total weight on Earth fell by about two thirds. Throughout these 5m years, no coal deposits formed, as there wasn’t sufficient plant 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 5m years, the world was trapped in this hothouse state.

[D] The sediments preserved in these cliffs were laid down in the early Triassic period, just after the greatest mass extinction in the history of multicellular life that brought the Permian period to an end 252m years ago. Around 90% of species died, and fish and four-footed animals were more or less exterminated 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 near-lifeless state for the following 5m years.

[E] Could it happen again? Two parallel and contradictory processes are in play. At climate summits, governments produce feeble 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 were extracted, their combustion would exceed the carbon budget governments have agreed sevenfold. While less carbon is contained in these reserves than the amount produced during the Permian-Triassic extinction, the compressed timescale could render this release just as deadly to life on Earth.

[F] Everything now hangs on which process prevails: the sometimes well-meaning, but always feeble, attempts to limit the burning of fossil carbon, or the ruthless determination—often on the part of the same governments—to extract as much of it as possible, granting the profits of legacy industries precedence over life on Earth. At the climate summit in Egypt, a nation in which protests are banned and the interests of the people must at all times cede to the interests of power, we will see how close to the cliff edge the world’s governments intend to take us.

[G] The second phase appears to have been driven by global heating. By 251.9m 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 fissures, into rocks that were rich in coal and other hydrocarbons. The heat from the underground lava cooked the hydrocarbons, releasing vast amounts of carbon dioxide and methane. Temperatures are believed to have climbed by between 8°C and 10°C, though much of the second phase of extinction might have been caused by an initial rise of between 3°C and 5°C.

【G1】_____→【G2】__→A→【G3】__→C→【G4】__→【G5】_____

【G3】