The book as a whole is beautifully written. Here's a small sample.
In fact, much of the planet was probably uninhabitable. The ancestor ocean to the Atlantic had been closing since the Ordovician, and by the Permian this marriage of the continents was consummated: the planet's landmasses were reunited, after hundreds of millions of years apart, to form one giant supercontinent stretching from pole to pole. The endless interior of this supercontinent was savagely bleak and arid -- a sort of global North Dakota -- with unearthly heat and ferocious cold, virtually untouched by rain. This was Pangaea.
At what they interpreted to be the boundary between the Permian and the Triassic, the therapsid world all but vanished in what looked to be a timescale of thousands of years, not millions, as had been previously thought.
Ward1, inspired by the Alvarez Asteroid Impact Hypothesis, sought to make a name for himself here in these ominous layers between the reigns of the fallen gorgonopsids and the surviving Lystrosaurus. He was after the debris from a catastrophic asteroid collision that could explain the devastation. He hunted for a layer of iridium, bits of fallout ejecta - anything to explain the sudden death of the biosphere. But he couldn't find it. What Ward and others found instead at the end of the Permian was a wild swing in the carbon cycle.
Where did all this extra light carbon in the atmosphere come from? There are a few ways to increase this reservoir. One way is to kill all the plants, plankton, and animals in the world. Plants are picky about their carbon and prefer the isotopically lighter stuff, locking up a vast amount of the world's supply. So too for plankton. And since animals eat those plants, and carnivores eat the animals that eat those plants, the entire living world pulls a huge amount of light carbon out of the system.
... when almost all the plants and animals in the world die, that lighter carbon is no longer locked up in trees and in plankton blooms and animal flesh and there's more of it left over in the atmosphere and oceans. Perhaps, then, this mass death explains the shift in the rocks to lighter carbon isotopes. But the carbon isotope swing at the End-Permian mass extinction is so severe that many other scientists think that the collapse of the biosphere alone isn't enough to explain it.
When the Industrial Revolution began in the eighteenth century and enormous coal measures were ignited in British factories, the world's atmospheric balance of carbon shifted toward isotopically lighter values, reflecting this huge injection of CO2 from fossil plants. This is another, more straightforward way to get the signal found in the rocks of the End-Permian: simply inject huge amounts of carbon dioxide into the atmosphere.
As Ward said, it doesn't matter whether carbon dioxide comes from "Volvos or volcanoes." At the End-Permian, there were plenty of the latter.