But the coup de grâce had been the giant magma plume that had burst, unexpectedly and explosively, through the crust beneath Yellowstone.

It was an explosion that had been ten thousand times as powerful as all mankind’s nuclear weapons, at their peak, ignited together. From a caldera the size of New Hampshire, blazing material had punched out of the atmosphere — some even entering low orbit — most of it falling back as giant fireballs which ignited what was left of the Earth’s vegetation.

And from the crater itself a huge fireball, followed by a dust plume, had swept up to the stratosphere, and added to the soot and dust from the burning forests to create a planet-covering pall of darkness.

Lights out, all over the Earth.

The atmospheric shock-heating was enough to cause oxygen and nitrogen to combine to nitrous oxide, which had combined with rain water to make acid; and enough acid rain had fallen on the planet to make the top three hundred feet of the oceans sufficiently acidic to dissolve calcareous shell material, so driving still more orders of life to final extinction. The food chains, already tenuous, had finally collapsed. Death soaked the planet, starting with the phytoplankton.

Ash falling, all over the Earth, like the thin layer that had been found in the rocks following the Cretaceous extinction, once puzzled over by scientists like Henry in bright, clean labs…

The magma plumes, giant wellings-up in the Earth’s molten substance that originated as deep as the core-mantle boundary, had been significant in Earth’s deep history. They had shattered continents, breaking up the Pangaea supercontinent, splitting Gondwanaland into two halves, splitting India, Madagascar and Antarctica from Africa. But all that had taken hundreds of millions of years. Now, the plumes” violence was manifested on timescales of mere decades, even years.

There was the mountain-building event in Antarctica, for instance, where the Indo-Australian plate had suddenly decided to set off south. More of the great magma plumes under Earth’s hotspots had come boiling through the crust, at the Canaries, under the tsunami-lashed wreckage of Hawaii, under Iceland. And the rift valleys all over the Earth had started to open up, in east Africa and Lake Baikal and the Red Sea, the continents just splitting apart. The river Rhine had disappeared into a crack in the ground, and then the graben through which it once flowed started to bubble with new ocean-floor plate.

What all the volcanism was mostly doing, in addition to killing people and boiling the seas, was pumping out a new atmosphere for the Earth: an unwelcome air of carbon dioxide and sulphur dioxide and hydrogen laced with arsenic and chlorine, that would, the estimates went, finish up ten times as thick as the old nitrogen-oxygen one. Immense greenhouse cycles had already started, and the oceans were evaporating and would soon start to boil…

And Henry’s beloved Earth was turning into what Venus used to be.