Interior of the Moon and Geologic History of the Moon

          Before the Apollo missions we knew almost nothing of the geologic history of the moon. The Apollo missions returned nearly half a ton of rock and soil samples. Close observation and analysis of these samples show that they contain minerals SIMILAR to those of Earth rocks BUT NOT exactly the same!

          This evidence refutes some theories of formation.

For example:

          If the moon simply broke off the Earth, then we should expect the moon to have the same proportion of minerals of the same type. We do not see this in the evidence though. The minerals are similar BUT NOT the same. They are different enough to make it unlikely that the moon was made directly from a large chunk of the Earth breaking off. For example: many minerals incorporate water into the structure of the mineral , water IS NOT found in similar minerals on the moon.

          Also, if the moon formed somewhere else in the solar system or outside the solar system, and was captured by the Earth's gravity, we would NOT expect the mineral structure and composition to be so similar to those of Earth!

          The Apollo missions performed MANY geologic experiments and left quite a few scientific instruments on the moon's surface. One of the most important experiment/ instrument projects of the Apollo missions was Seismology. Seismology is the study of waves that move through solid materials (like rock). By studying earthquakes, seismologists are able to determine the internal structure of the Earth.

          By studying the seismic record of the "MOONQUAKES" scientists were able to determine the internal structure of the moon! The moon appears to be built like this:

          It has a crust about 65 km thick, a mantle about 1000 km thick, and a core that is about 500 km in radius.

Image from Astronomy 161
by Dr. Stephen Daunt Univ. Tenn.

          A limited amount of seismic data suggests that the outer core may be molten.

          It has no magnetic field to speak of, but magnetization of Lunar rocks suggests that it may have had a larger one earlier in its history.

          Most Lunar seismic activity appears to be triggered by tidal forces caused in the Moon by the Earth.

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