They're called catastrophists, a group of British scientists who question many of the aspects of Darwinian evolution and argue that life on Earth and the geology of the planet have been constantly reshaped by asteroid strikes and other external shocks.

The latest sally from the catastrophist camp comes from the astronomer and mathematician Chandra Wickramasinghe, who told a scientific congress in California in July that he had found microbes in air samples scooped up by a balloon flying 25 miles (about 40 kilometers) above the Earth's surface.

Mr. Wickramasinghe, director of the department of Astrobiology at Cardiff University in Wales, said it was the first positive identification of extraterrestrial microbial life outside the atmosphere. The fact that a major British university has set up a department dedicated to a theory still regarded with much skepticism and hostility in the academic community is one indication of how accepted catastrophist ideas have become in British science.

There is no school of catastrophists as such in Britain. They are a loosely linked community of scientists drawn together by the gravitational pull of common interests, and who occasionally work together on joint projects or books. "There is no sense in which we come together to push a common view," said Mark Bailey, an astronomer who is director of the Observatory at Armagh in Northern Ireland, now a center for catastrophist thinking. "We are really individuals," he continued, "although most of us have worked together in different combinations, so in that sense we get on well with one another."

Catastrophism has never had much of a following in the United States, partly because of the debate between creationists and evolutionists, and partly because of the cultish influence of Immanuel Velikovsky, a pseudo-scientist who believed ancient myths could be explained by a near collision between Venus and Earth.

Comment: Interesting how in many cases in our society, person who cultivates deep and original (interdisciplinary) thinking in others is immediately labeled as having cultist influence with all the implied, negative and distorted, connotations. Read The Science Cartel vs. Immanuel Velikovsky to learn more about the man who became the target of nearly universal abuse and derision.

Because of the impact of the Velikovsky affair in America, "it is very hard for practicing scientists there to embrace the concept that catastrophism is really an ongoing process," Mr. Bailey said. On the other hand, the Society for Interdisciplinary Studies in Britain, which Mr. Bailey described as "a broad church," includes some Velikovskians.

Mr. Wickramasinghe and his mentor, the astronomer Fred Hoyle, have long argued that diseases like influenza that strike suddenly and simultaneously at many places around the Earth arrive here from space. They say that bombardment by external viruses or bacteria is a more logical explanation of life on Earth than the Darwinian view that micro-organisms evolved into higher life forms by constant replication and evolution.

While the Venus theory has been dismissed, two other British astronomers, Victor Clube and Bill Napier, developed the theory that the Earth is orbiting in the tail of a giant destroyed comet, and is under constant bombardment by bits of cometary debris, ranging from dust to sizable rocks. Occasionally, they say, it is hit by a particularly large chunk of rock, like the asteroid that fell in Siberia in 1908, or possibly a huge body that resulted in the extinction of the dinosaurs.

A leading astronomer of the last century, Ernst Opik of Estonia, who was the first scientist to compute the collision probabilities of comets and asteroids against planets, worked at Armagh from the 1940s to the 1980s. His grandson, Lembit Opik, a member of Parliament, successfully helped lead the scientific campaign that led the British government to set up the official Task Force on Potentially Hazardous Near Earth Objects.

Another leading catastrophist is Mike Baillie, an expert in early climate change, at Queen's University in Belfast. Mr. Baillie starts from scientific grounds, such as the measurement of tree rings and the examination of ice core samples, and then delves into mythology to find out if legends can throw light on the extraordinary, perhaps catastrophic climatic events revealed by the records. In a book, Exodus to Arthur, Mr. Baillie asks whether the simultaneous emergence of legends about dragons in China and angels in Western mythology were common reactions to the appearance of a comet.

Mr. Baillie points out that contemporary accounts at the time of the Black Death, which killed one third of Europe's population in the 14th century, mentioned droughts, floods, masses of dead fish, earthquakes, sheets of fire, stinking smoke, huge hailstones and blasts of hot wind - all possible descriptions, he said, of a close encounter with an asteroid or comet.

One record spoke of a large bright star over Paris, and another said that the sky looked yellow and the air red because of burning vapors. Tree ring studies reveal evidence of massive climate disturbance at the same time, Mr. Baillie added.

Catastrophism began receiving a fairer hearing in the 1980s after Walter and Luis Alvarez published an article in Science proposing that the extinction of the dinosaurs had been caused by the impact of an asteroid about six miles in diameter.

This was later linked to the crater, about 110 miles in diameter, identified in 1990 at Chicxulub in the Yucatan Peninsula of Mexico. About 130 such craters have now been identified on Earth. In 1994, scientists watched at least 21 large fragments from the Shoemaker-Levy 9 comet plunge into the surface of Jupiter, throwing up fireballs as big as the Earth. That, and a mass of research culled from space observation, lends some credence to the catastrophist view that a future disastrous impact on Earth is not a question of if, but when.