How Did The Moon Come To Be?

If you have read my work before, you might know of my keen interest in the topic of Entropy. Research into entropy is a slippery slope; one topic leads to another, and I often find myself going down a rabbit hole, wondering how I spent so much time learning so little!

The latest rabbit-hole is my investigation into the formative years of the Earth. From what we know, the Moon did not exist during the early life of the Earth. That is crazy, right?! When I first learned this, I remarked:

“Wow! Imagine a time when there was no moon in the sky; that must have been strange.”

In hindsight, I find this remark quite ignorant (you’ll learn why later in this essay). But nonetheless, it was an important remark. You see, hidden deep inside that ignorance is curiosity — something very valuable.

I am a strong proponent of encouraging curiosity even at the cost of ignorance.

Curiosity is the flame that drives the engine of knowledge.

Before presenting what happened during the Earth and the Moon’s formative years, I feel the need to differentiate between what we know about this topic and what we think we know.

The Limits of Scientific Investigation

It should come to you as no surprise that human history does not date back to billions of years. As a result, we cannot say much about that time with one-hundred percent certainty.

What we can do, however, is make use of the nature and environment around us and combine it with our scientific knowledge thus far to come up with educated guesses.

In more formal terms, we call these “scientific theories”. One of the good things about a theory is that it is allowed to fail.

For instance, if we observe that the sky is blue, a scientific theory might try and explain why it is the way it is. But in the future, we might learn something new about the phenomenon that does not align with the existing theory.

That theory would then fail, and scientists would come up with new theories that would take its place.

The job of a scientific theory, then, is to explain scientific phenomena with no contradictions to everything we know currently about the topic. As better theories contend to displace the existing ones, science pushes its own boundaries, and we progress as a civilisation.

Now that I have gotten the “caveat” out of the way, it is time to dive into the main topic.

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The Hadean Period

Our journey starts immediately after the Sun was formed. At this time, our solar system must have been a very chaotic environment, with the debris from the formation of the Sun still floating around.

This interesting thing about the left-over debris is that it likely got compressed into a disc along a plane around the Sun. At this point, the natural effects of gravity would have started to kick in.

The bigger the object, the higher the gravitational pull is. Consequently, the chaotic environment would have featured awesome crashes between the left-over fragments.

Some of these collisions would have led to smaller dust clouds, and some would have led to bigger objects like planets, asteroids, etc. And one of these must have been the Earth.

The first half a billion years of the Earth is often referred to as the Hadean period. Hades was the Greek God of the underworld. Needless to say, the Hadean era on the Earth refers to a deadly environment featuring erupting volcanoes, flowing lava, and poisonous gases.

There are some alternate theories, however, that suggest a much more conducive environment in the early days of the Earth. This comes in the wake of the research on zircon crystals, which typically form when molten lava cools down and solidifies.

The really cool thing about the zircon crystals is that they are very long-lasting and extremely durable. Furthermore, they capture information (by locking-in impurities) about their environment in the moment they were formed. For this reason, they are sometimes nick-named “time-capsules”.

Based on these findings (especially the zircon crystals from Australia), scientists have speculated that the ancient Earth may very well have been a calm water world.

Regardless of whether the ancient Earth was raging with fire or calm with water, we are pretty certain that the situation changed drastically after a specific event.

The Encounter with Theia

There are several scientific theories that contend to explain how the moon came to be. However, almost all of them have one common point — Theia.

About 4.5 billion years ago, roughly fifty to one hundred million years after its birth, the Earth must have collided with a Mars-sized object (a protoplanet) we call “Theia”.

This impact must have been so violent that the Earth’s entire crust must have been vaporized, also destroying Theia in the process. Consequently, a cloud of gas and dust would have ended up departing from the collision thousands of kilometres into space.

Part of this cloud of dust and gas must have compacted due to gravitational forces, which ultimately must have led to the birth our friendly planetary satellite — the Moon.

Now, when I express phrases like “the Earth’s entire crust must have been vaporized…”, it might be pretty hard to imagine as it is not a regular phenomenon in our lives.

So, to give you some perspective, I suggest you checkout this mind-blowing supercomputer-based simulation by NASA that graphically illustrates one possible angle of the story:

As one of the commenters in the video points out, the more you look at it, the more the collision seems like it involves two fluid droplets rather than two solids because of the energy involved.

The first time I saw this simulation, it had such a deep effect on me that I saw it again and again in my dreams!

At this point, if you are the sceptical type, you might be asking:

“Hang on a minute! How are we able to describe an event like this with such detail? What proof do we have that something like this happened?”

If that is you, I understand and encourage your scepticism. Let us try and address how science operates in this area.

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The Detective Gets to Work

You may be aware of the race between the United States and the Soviet Union (USSR) to explore the moon in the 1960s and 70s. But did you know that the Apollo missions (from the United States) alone gave us approximately 382 Kilograms of lunar samples? That is a LOT of information.

Compared to the Earth, the effects of time work on a much slower scale on the moon. Any close-up picture of the moon reveals the famous craters on its surface.

A more interesting fact is that the Earth had similar craters at some point in its life. You see, after the Moon’s birth, both the Earth and the Moon were bombarded by smaller meteors.

All the geological activity on the Earth ensured that its wounds (craters) healed, whereas the Moon’s marked lack of activity like eroding winds meant that its scars were healing at a much slower rate.

Although this is bad news for the Moon’s complexion, it is great news for science. From the lunar samples we collected, scientists were able to learn that the chemical composition of the Moon rocks was very similar to the Earth rocks (backed by the data from oxygen isotopes as well).

This essay is supported by Generatebg

Furthermore, we are currently able to derive the mineral composition of the Moon’s surface based on the light it reflects. It turns out that the Moon contains ample amounts of anorthosite, which floats on top of magma as it cools. This indicates that the Moon must have formed from a big impact which resulted in a magma ocean on its surface.

I could go on and on with the list of evidence we have, but it would be too boring. The short version of it is that we have been collecting evidence and are constantly applying our knowledge to come up with the most coherent theories. And the best theory we have about the birth of the Moon is the Earth’s encounter with Theia.

Does this mean that we have reached the end of our lunar investigation? Well, not quite. There are still a couple of interesting things that I wish to share with you.

The Lingering Effects

During the Moon missions, we placed reflectors on the moon’s surface. Using these reflectors, we are able to measure that the Moon is drifting away from the Earth by approximately 3.8 centimetres per year.

What this means is that the Moon likely formed much closer to the Earth and that the Earth’s spin rate was also much higher in the past.

When you think about the fact that the tides in our oceans are, to a large part, caused by the gravitational forces between the Earth and the Moon, it is easy to take the current situation will last forever.

But the harsh reality is that the Earth’s spin-rate is slowing down and the Moon is slowly drifting away.

Speaking of tides, we have grown accustomed to the warm summer months and the cold winter months. We experience these seasonal variations because the angle of sunlight changes throughout the year. Do you know what causes this change in angle?

It is the Earth’s tilted axis of rotation — the summer sun rays are more direct and the winter sun rays are more slanted. What do you think is the cause of the Earth’s tilted axis of rotation?

The currently dominant theory suggests that the Earth’s collision with Theia not only birthed the Moon, but it also led to the Earth’s tilted axis.

If this is indeed true, then the Moon is also the source of our seasons (not just tides)!

On that note, I wish to conclude this essay. I humbly thank you for your interest and hope your curiosity burns bright!

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Further reading that might interest you: 

• Fermi Problems: How To Deal With Huge Numbers?
• How To Use The Superellipse For Elegant Designs?
• How To Really Use The 12-Hour Clock?

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References: NASA and Brian Greene.