Leading article: Bolt from the blue

Once upon a time there was the Big Bang theory of the origins of the universe. Now, you could say, we have another, more local, "big bang" – for the origin of life on Earth. According to scientists in Arizona, the crucial components necessary for life to start may not have been generated by our own planet in the first instance, but come from somewhere deep in outer space, carried by the barrage of meteorites that crashed into the earth four billion years ago. The key is the discovery that a meteorite was capable of providing nitrogen-containing ammonia.

In one way it might seem disappointing that the Earth was not self-sufficient and may not have produced its own life. But perhaps we should not be so surprised. Our planet, at that time, was an extremely inhospitable place, hot and devoid of oxygen. That the vital conditions may have come together by chance, in part, literally as bolts from the blue, brings a satisfactorily quixotic aspect to scientific study – and, happily, hammers some more nails into the coffin of Intelligent Design.

But it is not entirely consoling. If the humans of today are the consequence of a protracted and haphazard bombardment from outer space, will capricious extraterrestrial intervention also determine the end? And will it be another bang, or a whimper?