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.

crater density used relative dating-24

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.

Earth has over 170 impact craters on its continents with the 1.2-km diameter Meteor Crater in northern Arizona being one great, well-preserved example.

Even Venus with its thick atmosphere has impact craters, though they all have diameters measured in kilometers because smaller projecticles burn up in its atmosphere.

Select the photographs to display the original source in another window.

There are still small chunks of rock orbiting the Sun left over from the formation of the solar system.

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.

Most of the impact basins---craters measured in hundreds of kilometers---were made during this time.