THE END OF LIFE ON EARTH

摘要

When it comes to what could wipe out all life on Earth, asteroids and comets are the likeliest culprits. If that doesn't do it, a swollen sun will (see "The end of the solar system," page 26). In the short term the greatest threat comes from comets, says Peter Ward at the University of Washington in Seattle. Comets hit at three times the speed of asteroids, he says, so they pack more of a punch. "Hale-Bopp is 50 kilometres in diameter. Had it hit, there would be no life on Earth."