A comet from the deep space far beyond Pluto probably won't smash into the Earth and obliterate all life, reassuring researchers said today. New calculations have determined that most extinction events that have occurred over our planet's history probably weren't caused by killer comet showers, which bodes well for the future, too. The findings are both welcome and well-timed since only last week an object dramatically smashed into Jupiter; many researchers believe the culprit was a comet. In the new study, published in Science, researchers focused on long-period comets, which