Pummelled into life

Life on earth may have started after an asteroid banged into her. Scientists at the Scripps Institution of Oceanography in California say that an asteroid collided with Earth between 3.6 and 4 billion years ago, thawing her frozen oceans and creating the right conditions for life to begin humming (New Scientist, Vol 141, No 1915).

The scientists believe that Earth's surface was infested with icepacks because the sun was 20 to 30 per cent fainter 4 billion years ago. They suggest that only the death impact of an object 100 km in diameter could have released enough energy to melt all the ice, thus sparking off the magical chemistry of life.