The Sixth Extinction: An Unnatural History by Elizabeth Kolbert
Reviewed by Caspar Henderson
One 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. As it hit with a force equivalent to more than 100m megatons of TNT, or about1,500 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.
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. 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. 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.
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