Extinction!

The death of the dinosaurs wasn’t unique. There have been 17 major extinctions of life during the past 600 million years. And, in most cases, an asteroid probably wasn’t to blame. The answer may lie in great volcanic eruptions.

Extinction has always been a controversial subject. Even after decades of intense study, researchers are still arguing over the cause of the best-known mass extinction, the ‘death of the dinosaurs.’ And there’s a topical slant in the idea that - even today - species are regarded as "endangered" if they are relatively susceptible to extinction. Then too, what thinking person could have avoided wondering whether our own species is slated for extinction and, if so, how long we have before we meet our fate?

The disappearing Mammoth

Two centuries ago extinction held centre-stage in an even more fundamental debate: whether the Bible should be interpreted literally. The bones of a very large fossil elephant (a ‘Mammoth’) had been collected in the then new world of North America. Discussing the Mammoth at the National Institute of Sciences and Arts in Paris in 1796, the French anatomist Baron Georges Cuvier argued that the bones belonged to a unique species of which no living examples were known. It was extremely unlikely that such a large animal could have gone undetected if its descendants had survived to the present day, so Cuvier pronounced the species extinct.

This conclusion contradicted religious dogma of the time. A benevolent creator, it was assumed, would not allow any of his creation to disappear from the Earth. In this way, Cuvier fired off one of the first salvos in a debate between theologians and natural historians that culminated 60 years later with the writings of Charles Darwin - and still continues in some quarters of society to this day.

Observing extinctions

Since Cuvier's time, extinctions have studied primarily by palaeontologists - scientists who investigate the remains of ancient life. For all that is said in popular books, articles and television programmes, the study of extinction is a surprisingly problematic and young field of inquiry. Extinction is one of the most common observations in palaeontology, but it remains very difficult to understand precisely why a particular ancient plant or animal species went extinct.

Much of this difficulty stems from the way that scientists ‘observe’ an extinction. Stated rather badly, we study extinction by observing what isn’t there. When we collect a fossil from a rock deposit, we assume that the species represented by this fossil lived at the place and time the rock was formed. If we sample a younger deposit and find that the species is not present, and if it never reappears in still younger deposits, we assume the species has become extinct, and that the time of extinction corresponds to the date of the youngest observed fossils.