PLANETARY SCIENCE: Beating Up on a Young Earth, and Possibly Life

Lunar meteorite analyses reported on page 1754 of this issue reveal a burst of impacts on the moon 3.9 billion years ago and nothing before that; the cosmochemists conclude that the moon and Earth endured a storm of impacts 100 times heavier than anything immediately before or after. Such a lunar cataclysm would have scarred the moon with the great basins that now shape the man in the moon. On Earth, the same bombardment would have intervened in the evolution of life, perhaps forcing it to start all over again.