As the work of Dr. Burgess documents, when this magma started spreading into the shallow crust of Siberia, it intruded into one of the world’s largest coal basins, cooking huge deposits of carbon-rich rocks. The superheated fossil fuels then ruptured at the earth’s surface in spectacular gas explosions, as documented by a team led by the Norwegian geologist Henrik Svensen.

Though volcanoes in Siberia had already been erupting for around 300,000 years, Dr. Burgess’s work indicates that it wasn’t until the magma started burning through fossil fuels on a colossal scale that the mass extinction began. The carbon dioxide was delivered to the atmosphere just as effectively as by any coal-fired power plant or minivan muffler today.

In the resulting chaos, as temperatures rose and life died in the acidifying, oxygen-starved oceans, the planet nearly lost its pulse. I asked Dr. Burgess what a time traveler visiting the End-Permian earth would have experienced. “It would be hot and it would be terrible,” he said, laughing.

Though the asteroid that would wipe out the dinosaurs 186 million years later might get more attention, the Great Dying dwarfs that catastrophe in destruction. It brought about the end to a less well-known but similarly fascinating, and much older world — a supercontinental wilderness stocked with an odd collection of uncanny pre-mammal forbears and, in the seas, an archaic hallucination of shells and tentacles that had prevailed since the dawn of animal life.

Today humanity plays the role of that primeval Siberian supervolcano, burning through the world’s ancient stores of carbon, long buried underground in the form of oil, coal and natural gas. Though there were likely other killers afoot in the Great Dying — like ozone-destroying halocarbons, acid rain and a heavy dose of toxic heavy metals raining from the volcanic smog — it was the chemistry-warping pulse of carbon dioxide that has attracted the most suspicion for its role in nearly ending the world. And we have only to look at the modern ocean to see why.

Excess carbon dioxide reacts with seawater to make it inhospitable to the animals that use carbonate to build their skeletons. Our modern oceans have already become 30 percent more acidic since the start of the Industrial Revolution, and the shells of fluttering planktonic snails — which form a foundational part of the food web in the Antarctic and the Pacific Northwest — have been found pitted with holes in our newly souring seas.

By 2050 the Southern Ocean will no longer be able to host those creatures, which also form a critical part of the diet of salmon. Acidification will also doom, perhaps by midcentury, the already ailing coral reefs that host 25 percent of the ocean’s biodiversity. And the world’s shallow oceans are losing oxygen as the planet warms and nutrient pollution pours in from agricultural heartlands and urban watersheds. Paleontologists have seen all these changes before.