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This assumes, of course, that the cratering rate has been fairly constant for the last few billion years.
The heavy bombardment of about 3.8 billion years ago must be taken into account when using the crater age dating technique.
The oldest fossil evidence of ancient organisms dates back to 3.5 billion years ago and evidence for biological activity based on isotopic ratios of carbon date back to about 3.85, even up to 4.2 billion years ago, though the carbon isotope ratio evidence is controversial.
The number of craters per unit area on a surface can be used to determine an approximate age for the planet or moon surface if there is no erosion.
Also the pressure from the surrounding solid rock squeezes the molten rock upward.
Molten rock contains trapped gases that expand as it rises causing it to rise even faster.
See the "Not Round" page from the THEMIS site for what can make an impact crater not round (links will appear in a new window).
Careful studies of how the craters overlap other craters and other features can be used to develop a history or sequence of the bombardment on the moons and planets. Worlds with less volcanism or erosion or tectonic activity in their history will retain more impact craters since the planet formed.
Worlds with more geological or erosional activity will have newer surfaces or craters that have been so worn away as to be unrecognizable.
The size of the craters having central peaks depends on the gravity of the planet or moon: on the Moon craters larger than about 60 kilometers in diameter have central peaks while the crater diameter on the Earth needs to be larger than just 1 to 3 kilometers.
Impact cratering was especially prevalent for the first several hundred million years after the planets formed as the planets swept up left-over material.