Current Cratering Rate

The above left figure shows the cratering rate for the Moon in units of number of craters with diameter > 1 km formed per year. The above right figure shows the cratering rate for the Earth. Note the frequency of the dinosaur killer, the KT crater. The cratering rate for the land masses on the Earth is roughly 10 times higher (can you think of reasons why?).

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History of the Cratering Rate

At left is shown the cumulative crater number as one looks back in time. So, if we start from now, 0 TIME BEFORE PRESENT, there are no craters formed yet. As we look back in time (moving to the left in the plot) we see more craters have been formed and counted. The dashed line shows how the cumulative crater number would increase if the impact rate was constant. Until around 4 billion years ago, the crater accumulation rate was slow and roughly constant. But starting from around 4 billion years ago, the crater accumulation rate jumped suggesting the impact rate also jumped! What could cause the rate to jump? This jump corresponds to the so-called Late Heavy Bombardment which likely produced the large impacts responsible for the maria and perhaps impacts that may have brought in much of our (the Earth's) oceans. Not apparent in the plot, there was also a smaller increase, around a factor of 2.6 in the impact rate about 290 million years ago.

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