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Originally Posted by vermonter
If all planet expand, why doesn't Venus show signs of expansion? Mercury? Why wouldn't the terrestial planets be the same size, if they are the same age? I'm not sure if Venus is considered one but Mars is a geologically dead planet. There isn't much activity going on what so ever.
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I think Venus does show it. Most of Venus has been resurfaced with magma, just as most of the Earth has been. The planets need not have started at the same size, and expansion may have been proportional to the initial sizes (at least according to decreasing G theories). Of course the gas planets will not show evidence of expansion in their surface features, even if they have expanded.
The statement that Mars is geologically dead puzzles me. Can we say for sure there is no 'seafloor' spreading along the Tharsis ridge, for instance?