The Sixth Extinction by Elizabeth Kolbert

It may seem like a diffuse, drawn-out affair to us as individuals but compared with many natural processes (for which animals and plants are, in Jacob Bronowski's phrase, equipped with 'exact and beautiful adaptations'), it is virtually instantaneous. Humans are affecting the Earth system in many ways, and have been doing so every moment for decades and indeed centuries. But first glances are sometimes misleading. The additional input of heat into the world's oceans resulting from greenhouse gases put there by the combustion of fossil fuels, for example, is equivalent to only about four atomic bomb detonations, or well under a tenth of a megaton per second. This event, known as the Cretaceous-Paleogene (and formerly as the Cretaceous-Tertiary) extinction, is counted as one of five mass extinctions over the last 500m years or so, where a mass extinction is defined as an event in which a significant proportion of life is eliminated in a geologically insignificant amount of time.Īt first glance, the footprint of industrialised humanity on the biosphere may look small compared with that of the Chicxulub asteroid. It took millions of years for life to recover and surpass its previous diversity, this time with a new ensemble of species that included our distant ancestors. Many scientists believe that about three-quarters of animals, including the pterosaurs, the mosasaurs and, as every child now knows, the non-avian dinosaurs were wiped out as a result. As it hit with a force equivalent to more than 100m megatons of TNT, or about 1,500 times the total content of the world's present nuclear arsenals, the asteroid sent a vast cloud of scalding vapour thousands of miles in all directions, and blasted more than 50 times its own mass of pulverised rock high into the sky where, as tiny particles, it incandesced and heated the entire atmosphere to several hundred degrees centigrade, killing almost everything unprotected by soil, rock or deep water.

O ne day around 66m years ago – it was in June or July if the evidence from fossilised pollen traces has been interpreted correctly – an asteroid somewhat larger than Manhattan ploughed into the Earth near what is now Chicxulub in the Yucután Peninsula, Mexico at 45,000 mph.

The Sixth Extinction by Elizabeth Kolbert