CHEMICAL COMPOSITION OF THE SURFACE
The moon appears to have formed from the same chemical elements, although in somewhat different proportions, as those that formed the earth. It has less iron, more of the substances that are hard to melt (refactory materials) - such as calcium, aluminum, and titanium-and less of the easily vaporized atoms and molecules (volatile compounds)-such as sodium and potassium-than the earth does.
The most common surface rocks are anorthosites (silicates mainly of aluminum and calcium), iron-rich basalts from the maria, and thorium-rich and uraniumrich rocks. No traces of water and no organic compounds, the indicators of living processes, were discovered in any of the lunar samples. I n fact the Apollo lunar rocks contain only tiny amounts of carbon and the carbon-based compounds from which life originates. With no water or oxygen present the minerals in the lunar rocks could not react with water to form clays or rust, nor did the iron react with oxygen to forrn oxides. The lunar highlands, which cover about four-fifths of the lunar surface, are the oldest preserved terrain. They consist mostly of material rich in aluminum and silicon and lighter than the mare basalts.
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