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For example, the highland regions on the Moon have ten times the number of craters as the maria, but radioactive dating (explained in the next chapter) shows that the highlands are approximately 500 million years older than the maria, not ten times older.At a minimum crater-age dating can tell you the ages of surfaces (which surface is older than another).
Volcanism is any eruption of molten lava onto the surface.
The molten rock has a lower density than solid rock so it rises.
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.
The last stage of that "sweeping up", called the occurred from about 4.1 to 3.8 billion years ago.
Impacts as large as the one that led to the demise of the dinosaurs in much more recent history were happening about once a month.
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.
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 first frame of a 3D movie flyover of Tycho Crater on the Moon as seen by Kaguya. It displays the classic terraced crater walls and central peak of a complex crater.