General Question

ETpro's avatar

Where did the Moon come from?

Asked by ETpro (34428points) August 7th, 2010

You would think we knew that, wouldn’t you? But do we? Silly answers aside, what do you think its origin is?

The Moon’s materials and makeup match Earth’s in some ways we do not see in, say, material found floating in the asteroid belt or objects that enter the Solar System from distant space. It has lots of oxides, for instance, indicating that oxygen and other gases were present in its formative stages. It’s oxygen isotopes are identical to those of Earth. It has water, now frozen, and may well have had more that was lost into space due to its relatively small mass, and thus low gravity. But it has no iron core as Earth does, and thus a much lower density (3.346 g/cc versus Earth’s 5.519 g/cc).

How old is the Moon? Why does it share some features with earth, but differ so substantially in other features? How did it get where it is today?

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38 Answers

saraSKELLINGTON's avatar

The moon was basically a meteor that got sucked into earth’s gravitational pull. The moon is pretty old, so I cant really tell you exactly though.

Cruiser's avatar

The moon is just a giant lint ball that has been collecting earth dust for 4,375,762 years.

marinelife's avatar

” 1984 when a new theory of the moon’s origin began to gain attention. The new theory stemmed from the recognition that the early solar system 4,500 million years ago was a more violent place than had been previously assumed. Rather than being filled with swarms of 10 km diameter planetesimals accreting directly into the four inner planets, it was realized that accreting matter would form embryonic planets with a large range of sizes in closely spaced orbits. The final stages of planetary formation would involve the coalescence of often rather large bodies, punctuating this era with giant impacts in which bodies of comparable size crashed into one another at high speed. The chaos of this era explains the wide variations in orbital inclinations, eccentricities, rotational periods and spin axis directions observed among the inner planets at present.

A giant impact provides just the right circumstances for a body with the moon’s peculiar chemical composition to arise. The vapor squirted from the contact point between the proto-earth and the impacting smaller protoplanet would consist predominantly of material from the mantles of the two objects and should exclude core metal. Condensing in space, the high-speed cloud of rock vapor would preferentially incorporate refractory elements, while volatile elements would be slow to condense and hence may be greatly depleted. The large amount of angular momentum brought in by the projectile would mostly go into the orbiting debris, although the proto-earth would also be spun up. From the angular momentum of the present earth-moon system the projectile must have had a mass comparable to that of the planet Mars.”

University of Arizona

CaptainHarley's avatar

The latest theories say that the moon was formed when a small planet collided with Earth. Vast quantities of material were ejected into orbit around Earth, containing material from both Earth and the planetoid. This material coalesced into what we now call the Moon.


Artistree's avatar

A very big cheese factory.

ucme's avatar

The big bang, wasn’t it?

ragingloli's avatar

God did it.~
No seriously, the moon is accumulated debris from an ancient collision of terra with another large object.

cockswain's avatar

@ETpro You’d normally be one of the first I’d go to with a question like that.

filmfann's avatar

While in the molten stage, a large body (comet, asteroid, rogue planet) hit the Earth, causing an equal sized Moon to emerge. We know the Moon came from Earth because of its rotation (we only see one side of the moon).
The giant impact that belched the Moon out of Mother Earth is probably the same impact that skewed its axis.

cookieman's avatar


Like everything else in this wonderful, magical universe of ours.


CaptainHarley's avatar


God uses an incredible variety of processes and actions to bring about change in the universe. Simply saying “God did it” does not adequately explain it.

cockswain's avatar

@CaptainHarley regardless of you define God, that is a great answer.

ETpro's avatar

@saraSKELLINGTON Why would the moon have Earth-like oxygen isotopes, then? Comets do not.

@marinelife Aside from Earth being more like 4.5 billion than 4.5 million years old, excellent answer. That’s my favorite postulate as well, as it seems to explain both the similarities and differences in Earth and its Moon.

@CaptainHarley GA and thanks for the link.

@cockswain Flatery will get you a GA even without trying to address the question. :-)

@filmfann GA. Any idea where the impact crater might be found?

ragingloli's avatar

marinelife said 4500 million which is the same as 4.5 billion
There is no impact crater, because the planet back then was largely liquid, and as with any liquidm the surface evens out eventually.

Nullo's avatar

I’ve heard four different theories.
First, the Moon was created In the Beginning.
Second, the Moon was a passing celestial body that got snared in Earths’ gravity well.
Third and, if you ask me, most preposterous that some time ago a passing celestial body failed to pass far enough, and smacked a hunk of Earth into space.
Fourth, that when the stew of superheated hydrogen that supposedly formed all of the celestial bodies cooled and coalesced, the glob at the 93,000,000 mile mark cooled into a planet and a moon, respectively.

ragingloli's avatar

Somehow I am not surprised that you would consider the explanation that is most likely to be true, the “most preposterous”.

Rarebear's avatar

The camp that states that there was a massive collision at the formation of the solar system creating a two body system is most likely the correct camp.

Here are a couple of interesting articles

There is a good story dramatized well in the HBO series “From Earth to the Moon” where Apollo 15 astronauts were looking for anorthosite , a mineral that was formed over 4 billion years ago. They found it and brought it back home, proving that the Moon is about as old as the Earth. It was the geologic find of a lifetime, and certainly the most important geologic find in lunar exploration (except, perhaps most recently for water on the moon). When I went too the Smithosonian National Air and Space Museum in Washington I looked specifically for a sample of anorthosite. They have on display a small sample of it in the middle of the Apollo exhibit. While everybody else was staring at the space suits and rocket ships, I stared for about 15 minutes at this stupid piece of rock and I unexpectedly broke into tears. I must have looked really weird.

kess's avatar

all physical perceptions manifest their reality within the mind.
For those things must first exist within this Mind otherwise there can be absolutly no perception of it.

The moon must first exist within you for you to perceive it’s existence, and it origin is the same as you yourself, through the manisfestation of Light (knowledge) from the begining.

We become aware of the things within us by this light (knowledge) but what it is not merely the knowledge that is important, for not all knowledge by themselves are profitable for the good.

More importantly we need Truth, for Truth show us the nature of all knowledge whether they be good or evil.

Rarebear's avatar

@kess Sorry, but that’s a load of crap. The moon is there whether we perceive it or not.

LuckyGuy's avatar

It was the result of a large asteroid impact with earth. 4..5 Billion years ago. Ejecta was flung into space and gravity caused it to coalesce. Its velocity and angular momentum determined the orbit. If it was going faster it would have been in a higher orbit. Slower and it would be closer. There is nothing magical about its distance from earth.

The moon rocks the astronauts brought back are mostly Anorthosite. That same material is found in old deposits right here on earth (Eastern Canada) that date to ~4 Billion years.

CaptainHarley's avatar


I understand the depth of that emotion.

cockswain's avatar

Has anyone heard how the formation of Earth’s moon is similar or different to moons of other planets? let me know if this should be its own question

Rarebear's avatar

@cockswain Well, it’s useful instead of thinking of individual planets, to think of planetary regions. The inner planets are all made of rock. I include the Moon in this as the Moon/Earth is basically a local biplanetary system.

The outer planets are made of gas, and their moons are mostly captured bodies in their gravitational well. In between is the asteroid belt, which is also made of rock. The asteroid belt may not have coalesced into a planet because of the tidal force of Jupiter.

Outside the gaseous planets are the Kuiper Belt Objects, of which Pluto is one. There are hundreds, maybe thousands of KBOs, and these are probably made of ice. That’s one of the reasons why Pluto was “demoted” from a planet—it made more sense. There are others, but that’s out of the scope of this question.

Outside the KBO is the Oort Cloud, where the comets come from.

So your question is complicated. The solar system was formed from an accretion disk, but the regions formed differently.

cookieman's avatar

@CaptainHarley: Notice the ~ at the end. I was kidding sir.

@kess on the other hand…

CaptainHarley's avatar


Ah! I didn’t pick up on that. Sorry!

cookieman's avatar

@CaptainHarley: Sorry. I didn’t mean to be so glib. It’s been one of those days.

ETpro's avatar

@ragingloli How right you are. @marinelife dis say 4,500 million which is exactly the same as 4.5 billion. My apologies to @marinelife for the misreading.

@Rarebear Thanks for the links. That camp seems to best explain the known oddities about our Moon. I’m the sort who tears up over space rocks as well. Think nothing of it. Re the differences in regions of our solar system, aren’t those likely a by-product of proximity to our sun’s enormous gravitational well, and if they are, wouldn’t the something similar likely hold true in planetary systems around other similar sized stars?

gondwanalon's avatar

We can only sit and wonder of such a colossal event. We dare to ask questions and are never satisfied with any possible answer as we suffer for not knowing the secrets.

I like the hypothesis that a huge planetoid, comet or meteor collided with the Earth while the Earth was in its early stages of formation. This not only formed the moon but perhaps also caused Pangea to form as the impact caused all of the Earth’s crust to get pushed up and into one mass (the super continent of Pangea) on the opposite side on the Earth. The slow breakup of Pangea continues today as the continents continue to drift in an effort to fill the void caused by the moon creating impact.

So we continue to gather information, speculate, theorize and dream during our journey to find the answers to our questions. When will we reach our destination where none of has been but each of us will recognize as soon as it appears on the horrizon? Tomorrow, perhaps. For it is the land of our dreams where the air is sweet and pure and its name is truth.

Dr_C's avatar

insert rimshot here

BoBo1946's avatar

@cprevite my vote goes for your answer! Plus, there is no way to explain the process by any human being. Only God can explain that.

Dr_C's avatar

@BoBo1946 I think you missed the tilde at the end of his remark…

BoBo1946's avatar

@Dr_C I could not answer that. Have no clue. Thanks for pointing that out.

Nullo's avatar

@ragingloli Shrapnel (even, I suspect, large pieces of shrapnel made of dirt and rock) is not typically as round as your average Moon. Hence my incredulity.

BoBo1946's avatar

@Dr_C also, thank you for the info…tilde will be my new word to use!

ETpro's avatar

@gondwanalon Our best guess is that super-continent formation and breakup is cyclical and there were predecessors to Pangaea. Pannotia came before Pangaea and Rodinia even earlier. We have some names for ones predating that, but the record gets more and more speculative as we dial back over 1.1 billion years. What we do know is we are slowly chugging towards one another so we can all hook up in another super-continent a few hundred million years in the future.

@worriedguy Fantastic link. Thanks for posting it.

ragingloli's avatar

Earth, and by extension, the debris that eventually formed the moon, was in a liquid state at the time. You know what happens when two water bubbles fuse together in zero G? They form a new round water bubble. It would have been no different for the moon.

Nullo's avatar

@ragingloli That’s better, then.

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