This is an image of Venus. Click on image for full size version (40K GIF) Image from: NASA

Like Mars, there is no plate tectonics on the surface of Venus. The surface of Venus does not *seem* to have changed or moved in billions of years. Unlike the case of Mars, however, careful examination of the evidence supports the idea that the surface of Venus may be active in a way that is very different from the Earth.

• 1.) An examination of the surface of Venus shows cratering at all latitudes and longitudes. Craters are wiped out when the surface of a planet moves. Heavy cratering stopped soon after the solar system formed, about 4 billion years ago, so a surface which still shows evidence of that catering has not changed in a very long time.
• 2.) Although heavy cratering has stopped, some cratering continues to this day. The impact of the SL-9 comet shows that planets can still be hit by objects in space. The cratering record of Venus is *very* peculiar in that
  • all surfaces are evenly cratered
  • the cratering rate is roughly the same as that of the Earth at present.
• 3.) Features which suggest a lithosphere in motion are present, but few on Venus.

This evidence suggests that Venus has a completely different cooling history than that of the Earth, and the entire surface is forced to change every few hundred million years or so.