Guide to Magellan Image Interpretation
Subduction of underthrust slabs, mantle plume upwelling and downwelling, crustal shortening, and rifting all probably play a significant role in the formation of surficial Venusian tectonic features.
Impact craters are found on both the plains and the highlands of Venus. Schaber et al. [1992] found the spatial distribution of craters to be highly uniform with a size-frequency distribution lower than those of the other terrestrial planets (except that of Earth), indicating a relatively young age of 0.5 Ga. The number of small craters is much smaller than that on other planets because of atmospheric filtering. One theory holds that the majority of Venusian craters appears pristine because the planet was resurfaced 0.5 Ga ago and there has been very little geologic activity and weathering since to degrade and destroy the craters [Schaber et al., 1992]. Phillips et al. [1992] found that the crater size-frequency distributions, locations, and preservation states implied a range of surface ages.I was wrong to assume old craters from 4 billion years ago. Apparently, half a gigayear is about it. Still, that's pretty old for what we're talking about.