Lunar Geology: Types of Moon Rocks

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  • 0:02 The Geology of the Moon
  • 0:25 Lunar Mare, Terminator…
  • 2:25 Basalt, Breccias & Anorthosite
  • 3:41 The Moon's Interior
  • 4:12 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will discuss the layers of the Moon's interior, the dark and light colored areas of the Moon's surface, the Moon's craters, and how moon dust has formed over the ages.

The Geology of the Moon

Sedimentary rocks. Igneous rocks. Metamorphic rocks. Everyone has at least heard of the geology of Earth. But what about Earth's best friend? Our Moon?

What's the geology of a celestial body upon which only 12 people have set foot? Although few people have stood on the Moon, we can use photographs, samples brought back from these voyages, and measurements to help us figure out the geology of Earth's best friend.

Lunar Mare, Terminator, and Craters

The surface of the Moon is split into two differently colored terrains, like a yin and yang. There are the dark gray regions called maria, which are lowlands on the Moon filled by dark lava, and the brighter, more heavily cratered lunar highlands called terrae.

The singular for maria is mare, which is Latin for sea, while terrae means land. Galileo called the dark regions maria (or seas) likely not so much because he thought the Moon had a ton of water on it but more likely because such areas simply looked like large bodies of water more so than anything else. What Galileo didn't know for certain is that these areas are actually large swaths of solidified lava created over four billion years ago.

Galileo also didn't know that the Terminator lives on the Moon. I bet you had no idea that Arnold Schwarzenegger was an astronaut from the future, did you?

I'm just messing around. The terminator is the division between darkness and daylight on the Moon. Near the terminator, the lunar crater looks quite spectacular -- just look at the images on your screen.

Such craters on the Moon formed when meteorites struck it over and over again. Some of these craters are tiny, as they were formed by micrometeorites. Others are just huge!

One of the largest craters on the Moon is called Clavius. It is 220 kilometers in diameter and has a depth of several kilometers. Most of the craters, regardless of size, are very old.

The debris that is ejected out of a crater as a meteorite hits a planetary surface is appropriately called ejecta. If the ejecta is blasted out in a specific direction, it can form bright rays on the lunar surface. Rocks that are ejected from a large primary impact can fall back down to the Moon to form smaller secondary craters.

Basalt, Breccias, and Anorthosite

Some of the lowland rocks the 12 men who stood on the Moon found are called vesicular basalt. They are a kind of porous rock, meaning a bunch of bubbles formed holes in the rock as the lava solidified. To me, this kind of rock looks like Swiss cheese as a result.

The highlands contain a kind of rock called anorthosite, a low-density rock made of aluminum and calcium silicates. Its light color is partially responsible for the contrast seen between the bright highlands and the dark lowlands. A third kind of rock that's found on the Moon is called breccia, a type of rock made of fragments of previously broken rock that have been fused together under the pressure of meteorite impacts.

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