Moons
Moons

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Moons

5.1 What we’ve learned about the Moon

Rocks are the key evidence for the Moon’s story. The meteorite-battered lunar highland rocks are more ancient than anything on Earth, and the ancient volcanoes on the Moon are better preserved than many modern volcanoes on Earth.

Dave Vaniman reflects on his experience of seeing rocks brought back from the Moon, the importance of the interaction with the Moon for the history of life on Earth and what we’ve learned about the Moon.

Last week you learned about the unique characteristics of the surface of our Moon and its exploration by Apollo astronauts. Now you will look in more detail at the rocks on the Moon’s surface and what they can tell us about the formation of the Moon.

It may surprise you to learn that the Moon rocks returned by the Apollo missions are still being analysed today. Unlike rocks on Earth, these samples have not been subjected to terrestrial alteration caused by water (on Earth, even in the desert, rocks on the surface become altered in a few years); neither have they been subjected to contamination by soils and windblown dust. The sophisticated analytical techniques of today allow us to find out more about these amazing samples than we could when they were first returned to Earth and one particularly exciting discovery (water) will be explored next week. This week, you will be introduced to the geology of the lunar surface and the rock types returned by the Apollo missions. You will also be introduced to how planetary scientists examine rocks under the microscope and how these are dated, in order to piece together the structure and formation of the Moon.

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DAVID VANIMAN
What struck me about lunar samples was how totally foreign they are to the materials I was used to. I've done a lot of field work. I've worked with granites, basalts, soils on Earth. But the things that I found in the first samples I saw from the Apollo 16 drill core were just stunning. Here were basalts, fragments of lava, that were almost four billion years old, and they were as fresh as if you'd collected them in Hawaii the day before. That just doesn't happen on Earth.
The Moon is a time capsule. It preserves rocks in states that just cannot be found on Earth. And that's one of the really intriguing things about the Moon, is it's a very, very old encyclopaedia. We can go back into events that occurred in the Solar System far earlier than the things that we're familiar with on Earth. We can see things that have happened that we have no record of on Earth. And in that regard, it's just a phenomenal repository of history. And when you get right down to it, at least in my perspective, geology is all about history on the very large scale. Not within the span of a human lifetime, but within the span of billions of years.
One of the key scientific questions that was in the forefront when the Apollo mission was being designed was, how did this thing form and what does it mean for us? Was it captured? Did it form along with us? Did it split off from the Earth? There is now something called a giant impact theory, the concept that a very large body at some point impacted the Earth. So there is an aspect of something coming from outside the Earth's regime, something then forming around the Earth as a result of the impact, and also with parts of it coming from the Earth. All of this seemed to play into this origin theory. And it's fascinating because no one had thought of stringing those things together. They were all considered separate, and the Moon was able to unify this.
The Earth is a complex system, and we still have poor understanding about what would happen if you tweaked part of that system. If you took away our Moon, what would really happen to the Earth? How would it have evolved? It would certainly be a different planet, but how different? Earth used to spin faster than it does now. And it has slowed down over time because of tidal drag from the Moon. It has affected the length of our day. It affects the cycles within the Earth's ocean. All of this shows up in the way that life has evolved on Earth - the way we adapt to day-night cycles, the way life in the ocean has developed. It has moderated the way that the Earth behaves in many ways. There should be many Earth-like planets out there. But we're really special because of this complex interaction and relationship we have with our Moon. It gives us a companion that steadies our dynamics in this habitable zone around the Sun. We don't have serious extremes of orientation that could really be a significant issue for creating an environment that is steady enough, stable enough, and favourable enough for life. And it's a real question - are we unique or not? How often does this happen? And how important is this relationship with our Moon? Is it really that critical? And I don't have the answer for that, and I don't think anyone else really does right now. But it's something that deserves really serious consideration, especially as we're looking at the role of Earth and life in the universe.
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