Moonquakes

On earth, the shaking of the ground from an earthquke is measured by an instrument called a seismometer. Four seismometers were left on the moon after the Apollo missions in the '70s, and they radioed back through 1977. Today they help bolster the theory that the earth and the moon did not form at he same time.

When the data was first recorded, there wasn't a computer fast enough to analyze it. Researchers spread the data in long, squiggly pages and analyzed it by eye, looking for evidence of moonquakes. Recently, the data was analyzed by modern computers. Here's a summary of what they found.

There are frequent moonquakes. Certain interior parts of the moon brake repeatedly, and the rate of moonquakes suggested that they are caused by the pull of tidal forces between the moon and the earth. Almost all of the deep moonquakes originate on the side that faces earth. The moon's crust is 25 percent thinner than earlier believed.

The moon's interior has a considerably different chemical make-up than the Earth's upper mantle. This supports the idea that the moon and the earth did not form at the same time, because if that had been the case, the two bodies would be expected to have similar. Link.