Country: United States
Date: April 2006
Why are impact craters rare on the earth?
It is not so much that the Earth somehow was not subjected to the same
meteor bombardment as the other planets and moons in the solar system.
Rather, because there is so quite a bit of geological activity on Earth
(wind, rain/erosion, volcanic activity, techtonic plates motion, etc.) and
human activity (building of cities, roads, etc), these activities tends to
"erase" such features over time.
Greg (Roberto Gregorius)
Scientists believe that the Earth was impacted in its past, and may once
resembled present-day Mercury and our Moon in terms of craters. Earth has
very active weathering and erosion, and a lot of rocks and land that were
around when the Earth was heavily cratered are no longer present. They have
long since eroded and became other rocks and sediments. We no longer have
the heavy bombardment thought to have been present in the early solar
and craters found now are likely to be more recent. So, impact craters are
rare on Earth because few impacts are occurring now, and impacts which
occurred in the past are long-since eroded away.
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Update: June 2012