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The Worst of Times

How Life on Earth Survived Eighty Million Years of Extinctions
Paul B. Wignall
Publisher
Princeton University Press
Price
£19.95
ISBN
9780691142098
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EXTRACT COPYRIGHTED MATERIAL

From A Time of Dying

If you could travel back in time 260 million years, you would find our planet had an unfamiliar geography. Nearly all of the landmasses were united into a single, giant continent. This was Pangea, and it stretched from pole to pole. On the other side of the world you would find a vast ocean, even larger than the present Pacific, called Panthalassa. Plunging into the ocean you would see some vaguely familiar groups— including mollusks, corals, and fishes—present in abundance, but as you strolled around the land, everything would look entirely strange. Large, lumbering, reptile-like creatures with faces covered in blunt horns ruled the world, and they crashed and blundered their way through vegetation composed of giant fernlike trees and conifers.

Despite the strange and superficially primitive appearance of terrestrial life, it actually represented a spectacular evo­lutionary achievement. This was the middle of the Permian Period, and for the first time, animals and plants had spread throughout the land and away from the wet habitats around rivers and swamps. This was the result of innovations, such as reptilian eggs and conifer seeds, that meant many organisms could now survive on dry land. In contrast, there had been few recent changes in the oceans. The Middle Permian ma­rine realm was rather like that of the Carboniferous Period, and it was not a great deal different from that of the Devonian Period before that. But this business-as-usual story was about to change. The first mass extinction in 100 million years was shortly to strike. The dominant land animals would be wiped out along with many of the ocean's most common species. This was a disaster, and it was just the first of a series of six ca­tastrophes spread over the next 80 million years and included the worst examples the world has ever experienced. By the end of this age of extinctions, life everywhere had changed profoundly. In the oceans, the entire food chain, from the smallest plankton to the largest predator, was totally trans­formed. It was the same story on land. Dinosaurs now ruled the roost while swift little mammals darted around their feet. With the singular exception of the mass extinction that removed the dinosaurs, 66 million years ago, life was never again to experience such traumas.

This book attempts to explain and understand this worst 80 million years in Earth's history, a time marked by two mass extinctions and four lesser crises. To put the Pangean trauma into context, it is important to note that five major mass ex­tinctions have afflicted the course of life. Scientists define mass extinctions as geologically brief intervals when numer­ous species go extinct in a broad range of habitats, from the ocean floor to forests, and at all latitudes, from the equator the pole. A true mass extinction represents global devasta­tion with no hiding place. The first of the "big five" occurred 444 million years ago, at the end of the Ordovician Period. It was a fascinating event, associated with a short but intense glaciation (making it the only mass extinction event to be clearly linked to a cooling phase), and I wish I had reason to write more about it here, but it is not relevant to our story. Number two on the mass extinction list happened 70 mil­lion years later, during the Late Devonian Period.