Page 54 - Curriculum Visions Dynamic Book

 This Apollo 16 lunar sample (usually just called “Moon rock”) weighed 128 grams when returned to Earth (but just a sixth of that when collected on the Moon, due to the Moon’s lower gravity).
The sample is a collection of broken fragments that have been fused together. This kind of rock is called a breccia.
This rock, like all lunar highland breccias, is very old (about 3.9 billion years), older than 99.99% of all Earth surface rocks.
Analyzing the rocks
The rocks that were collected by both the American and Russian missions to the Moon have been invaluable in adding to our knowledge of the Moon and have helped in developing a model of how it formed.
For example, it has been possible to date the rocks using their radioactive content.
As soon as a rock cools, any radioactive isotopes in it start to decay. If we know the rate of decay, the radioisotopes can be
used as a geological clock.
Isotopes of rubidium and strontium can
be used to date rocks that are billions of years old. Analysis of the lunar rocks showed conclusively that the Moon
has a long history during which its components have formed into a crUst, mantle, and core, and that many of the surface rocks are volcanic.
Highland rock samples were shown to be four billion years old. This proved the Moon’s crust was already solid by then. Because the Solar System is 4.6 billion years old, the formation of the Moon must therefore have occurred at an early date.
Samples of mare lavas show that the volcanic rocks are much younger than the highland rocks, and so it is believed that after the Moon emerged, it heated up enough internally for liquid rock to form.
The Moon’s interior
What is not so obvious is anything about the Moon below the surface. The Moon has an average density of 3.34 g/cm3. That is higher than the density of the Earth’s crust and about the same as that of the Earth’s mantle. It may possibly have a small metal core, but we simply
don’t know.
By studying its orbit, we know that the center of gravity of
the Moon is not quite in the center, but about 2 km toward the Earth. There are also more-dense and less-dense regions on the Moon’s surface. The higher-density areas are called mascons. These facts have been determined by examining the pattern of gravity of the Moon.
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