The Late Heavy Bombardment (LHB) was a period approximately 3.8 to 4 billion years ago during which the Moon, Earth, Mercury, Venus, and Mars were subjected to many impacts from space. The evidence for this and the dating comes mainly from analysis of the craters of the Moon and Moon rocks. It formed some craters the size of continents. This bombardment came after a relatively calm period of several hundred million years. It is not yet clear exactly what brought about the renewed bombardment. One possibility is that Jupiter's orbit shrank, causing it to clean out the outer edges of the asteroid belt, a portion of which would have been sent careening into the inner solar system. Or somewhere in the Solar System a big collision created a lot of flying fragments which became new asteroids. Recent computer models also suggest that resonances and perturbations caused by the four large outer planets settling into their current orbital configurations could have displaced large volumes of material into the inner solar system.

On Earth, the Late Heavy Bombardment would have produced:-

22,000 or more impact craters with diameters > 20 km

about 40 impact basins with diameters about 1000 km

Several impact basins with diameter about 5,000 km

with a serious environmental damage event about every 100 years.

External links

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• "Late Heavy Bombardment was asteroidal, not cometary," The Geological Society, March 4, 2002.
• Britt, Robert Roy, "Evidence for Ancient Bombardment of Earth," 24 July 2002.

Solar system | Impact events