Earth Is Near Moon

Earth Is Near Moon

All the evidence that the Crater Giordano Bruno was gouged out less than a thousand years ago, is inferential and indirect. The odds are against such an event happening in historical times. But the evidence is at least suggestive.

As the Tunguska Event and Meteor Crater in Arizona also remind us, not all impact catastrophes occurred in the early history of the solar system. But the fact that only a few of the lunar craters have extensive ray systems also reminds us that, even on the Moon, some erosion occurs (on Mars, however, where erosion is much more efficient, although there are many craters, there are virtually no ray craters, as we would expect). By noting which craters overlap which and other signs of lunar stratigraphy, we can reconstruct the sequence of impact and flooding events of which the production of crater Bruno is perhaps the most recent example.

Cosmic Rays. Attempt to visualize the events that made the surface of the lunar hemisphere we see from Earth. Image: © Elena

The Earth is very near the Moon. If the Moon is so severely cratered by impacts, how has the Earth avoided them? Why is Meteor Crater so rare? Do the comets and asteroids think it inadvisable to impact an inhabited planet? This is an unlikely forbearance. The only possible explanation is that impact craters are formed at very similar rates on both the Earth and the Moon, but that on the airless, waterless Moon they are preserved for immense periods of time, while on the Earth slow erosion wipes them out or fills them in. Running water, windblown sans and mountainbuilding are very slow processes. But over millions or billions of years, they are capable of utterly erasing even very large impact scars.

On the surface of any moon or planet, there will be external processes, such as impacts from space, and internal processes, such as earthquakes. There will be fast, catastrophic events, such as volcanic explosions, and processes of excruciating slowness, such as the pitting of a surface by tiny airborne sans grains. There is no general answer to the question of which processes dominate, the outside ones or the inside ones; the rare but violent events, or the common and inconspicuous occurrences. On the Moon, the outside, catastrophic events hold sway. On Earth, the inside, slow processes dominate. Mars is an intermediate case.