We are living in a time of highly elevated extinction rates
BRENT: In the normal course of events, extinctions should take place only very rarely. This is what scientists refer to as the “background extinction rate.” We are living in a time of highly elevated extinction rates. Among well-studied groups the figures are quite alarming — it’s estimated that a third of all reef-building corals, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles and a sixth of all birds are now vulnerable to extinction. Even schoolchildren know of animals that have gone extinct in their lifetimes, or that have been driven to the very edge of extinction. The Indian vulture is one example: populations have dropped more than 90% just in the last decade or so. The government has taken steps to address the cause of this decline, which is a drug that was widely dispensed to livestock, but vulture populations are so low at this point it’s hard to know whether they will ever recover.
Periods of very high extinction rates are called mass extinctions. There have been five major mass extinctions over the last half a billion years; these are known as the Big Five. Each of these events killed off something like three-quarters of the species on earth. The most recent was the extinction that killed off the dinosaurs. The Sixth Extinction is the name that’s been given to the current extinction event, though whether this one will be as severe as the Big Five remains to be seen.
