Heat Wave at the K-T Boundary?

Article excerpt

Heat wave at the K-T boundary?

The widespread death of microscopic ocean plants 65 million years ago could have triggered an extreme global heat wave that helped kill off roughly half the existing species of plants and animals, including the dinosaurs, at the Cretaceous-Tertiary (K-T) boundary. This scenario, derived from new calculations by scientists at New York University, is helping to bring into focus the series of climatic plagues that were dramatically changing the living conditions on earth at that time.

Scientists have spent years debating what catastrophic event let to the events at the K-T boundary. According to the leading-candidate theory proposed in 1980, a comet or meteor collided with earth, creating a global dust cloud that blocked out sunlight and cooled the planet for a period of up to several months.

More recently, however, researchers have realized that the climatic troubles would not have ended when the lights came back on. "What we're seeing is that the K-T boundary was a pretty complex event," says NYU's Michael Rampino. He and Tyler Volk have examined how the elimination of one type of life would have affected the climate.

According to the researchers, a catastrophic impact could have triggered the death of floating one-celled ocean plants, called calcareous nannoplankton. This, in turn, would have weakened the earth's ability to reflect radiation from the sun, raising surface temperatures by 6[deg.]C for several hundred thousand years. Such a rise would finish off many species that had survived the earlier changes in climate.

It was only recently that scientists discovered a connection between nannoplankton and the earth's climate (SN: 12/5/87, p. …