Now we have to worry about gamma rays, too. University of Kansas astrophysicist Adrian Melott told the annual meeting of the American Astronomical Society last month that the Ordovician extinction, which wiped out most of the species on earth 440 million years ago, was probably caused by a huge burst of gamma rays from outer space. A giant star around 10,000 light years from here exploded, and when the resulting gamma rays struck our planet, they destroyed the ozone layer and created a toxic brown smog that cut the sunlight reaching the surface in half. Over two-thirds of the species that then existed became extinct. Oh, and you can expect another such event every few hundred million years.

Perhaps we should just hope it doesn’t happen again any time soon, since there is actually nothing we can do about bursts of gamma rays. But the past twenty years or so have seen a whole series of discoveries about abrupt and catastrophic events that have hugely affected life on earth in the past, and some of them are neither unpredictable nor unstoppable.

Take asteroids, for example. Many of us know that it was a giant asteroid smashing into the Gulf of Mexico that killed off the dinosaurs 65 million years ago, making way for the age of the mammals. Fewer people know that it was probably another asteroid, smashing into what is now eastern Quebec around 200 million years ago, that opened the way for the dinosaurs. It killed off only half the species on earth, but it did eliminate the mammal-like reptiles that were then the dinosaurs’ major competition.

Attacking asteroids

At least 900 asteroids more than half a mile in diameter cross the earth’s orbit. Small but still potentially dangerous asteroids hit our planet all the time: one that struck north of Lake Baikal in eastern Siberia in September 2002 flattened 40 square miles of forest. (If it had come down over Moscow or New York, it would have killed millions.) So you would think that human beings would be trying hard to create a defence against this danger, would you not?

“If we’re due to be hit within a day, week, month or year, we’re not going to spot it,” said astrophysicist Duncan Steel of Salford University. “A 200-metre object plonking down into the Atlantic would effectively take out all the cities around the seaboards. Those smaller events occur rather more frequently — (it’s a) once every several thousand years event.” Steel believes, however, that this sort of disaster can be prevented: “If one’s due in 50 years, I think we could spot it...I’m optimistic that we have the scientific and technical capability to detect and divert it.”

And volatile volcanoes

Good luck, but there is already a well-known object — much slower-moving but vastly more massive — that could produce a tsunami big enough to drown all the cities that face the Atlantic, and nobody is even watching it. An enormous chunk of the Cumbre Vieja volcano on the island of La Palma in the Canaries has become detached from the main body of the island and is sliding slowly towards the sea. It suddenly dropped more than 4 yards in 1949 and then stopped, but it continues to creep seaward.

If it drops into the sea one day, a tsunami 60 yards high will reach the west coasts of Africa and Europe in an hour or two, and the east-coast cities of the United States of America in four hours. A few hours’ warning could save millions of lives, so you probably think that somebody is monitoring the movement of this mass of rock. Wrong. Those who have most to lose if Cumbre Vieja slides into the sea are paying no attention at all.

We are also paying little attention to global warming, and failing to monitor 90 per cent of the world’s 3,000 volcanoes even though a really big once-in-50,000-years explosion would cause the equivalent of a nuclear winter. (There’s nothing you can do about a super-volcano exploding, but at least you can have a few years’ warning to prepare.) It’s a kind of cultural lag. We have discovered that our world is a far more dangerous place than we ever dreamed, but we still can’t accept the reality of it.