Moon Geology

The lunar crust is a three layer cake affair, with an upper regolith, lower regolith, and then the mantle layer. The upper regolith extends from 3 feet to 60 feet in depth, and is the result of millions of years of constant bombardment of meteorites and geologic stress from heating and cooling. The lower regolith extends to a depth of 12 miles, and is made up of basalt rocks. Below the two layers of regolith is the mantle, consisting of less rigid material that is low in iron content. Scientists have postulated from the available data gathered from Apollo and unmanned lunar mis­sions that the core of the Moon is small and iron-rich.

There are three major types of features that dominate the surface of the Moon: impact craters, marias (or seas), and highlands. Most familiar are the many craters, caused by the eons of meteorite impacts on the surface. The wide, dark seas are composed of iron and titanium rich volcanic rock known as basalts. And the high­lands are made up of various types of silicate type rocks.

Unique to the Moon’s geology in the highlands, and not found on Earth, is the presence of a type of rock called KREEP. This acronym is formed from potassium (chemical symbol K), rare-earth elements (REE), and phosphorus (chemical sym­bol P). First discovered from the samples brought back by Apollo 12, KREEP is made up of normally incompatible elements, and represents part of the evidence for the formation of the Moon. The leading theory for the Moon’s formation is that it was formed from the remains of an ancient impact between the Earth and a Mars­sized proto-planetary body.

The Apollo missions provided detailed knowledge of the nature of the lunar soil and rocks, and evidence for the impact theory of the lunar genesis.