Philosopher and historian Thomas S. Kuhn has suggested that
scientific disciplines act a lot like living organisms: instead
of evolving slowly but continuously, they enjoy long stretches
of stability punctuated by infrequent revolutions with the
appearance of a new species--or in the case of science, a new
theory. This description is particularly apt for my own area of
study, the causes and consequences of mass extinctions--those
periodic biological upheavals when a large proportion of the
planet's living creatures died off and afterward nothing was
ever the same again. Since first recognizing these historical
mass extinctions more than two centuries ago, paleontologists
believed them to have been gradual events, caused by some
combination of climate change and biological forces such as
predation, competition and disease. But in 1980 the
understanding of mass extinctions underwent a Kuhnian revolution
when a team at the University of California, Berkeley, led by
geologist Walter Alvarez proposed that the famo