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The Giant Impact Theory  (Source:
Two new studies attempt to prove the Giant Impact Theory in different ways

Two different studies say they've found evidence supporting the theory that the moon was created from a collision between Earth and a Mars-sized body.

The Giant Impact Theory, which was proposed back in 1975, suggests that the early Earth and a Mars-sized planet called Theia collided with one another. This completely obliterated Theia, and its composition created a ring around Earth and eventually came together to create the moon.

While scientists have been able to explain how this event occurred, one major thing didn't add up: the composition of the moon.

Scientists long believed that for this theory to be true, the moon would have to be composed mainly of Theia's elements. Moon rocks from that were brought to Earth were studied, and surprisingly, they had the same types and amounts of elements that the Earth had, including titanium, silicon and oxygen. This didn't make sense, and has left the theory wide open for the last 30+ years.

However, scientists from Washington University in St. Louis managed to measure a small excess of a heavier variant of zinc in moon rocks from that were brought to Earth in the 1970s. They believe the excess is due to heavier zinc atoms condensing out of the collision's cloud faster than the lighter zinc atoms, and the vapor that remained escaped before it condensed.

This bit of sorting by mass is called isotopic fractionation, and it's what scientists have been looking for all along. This shows that the moon rocks were depleted of easily evaporated elements called volatiles, and a large collision could explain this depletion while other theories can't.

"The magnitude of the fractionation we measured in lunar rocks is 10 times larger than what we see in terrestrial and Martian rocks," said Frédéric Moynier, PhD, from Washington University in St. Louis. "So it's an important difference."

But the Washington University team isn't the only one to bring new evidence to the table. Robin Canup, a planetary scientist from the Southwest Research Institute Colorado, used Harvard scientists' findings to create a theory of her own related to the collision.

According to the Harvard team, which used computer simulations to create its theory, ancient Earth had to have been spinning too fast for today's 24-hour rotation. They suggested that early Earth and a body half the size of Mars could have collided where both were obliterated and combined elements to create both the moon and Earth's heavy iron core/lighter rock layers.

At a later point, Earth's rotation could have slowed due to the moon and sun aligning in a way that changed Earth's orbit.

Canup used the idea that Earth's rotation was slowed and came up with the theory that two bodies similar in size collided at a slow speed, and their materials merged to create the Earth and moon.

Source: Science Daily

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By Goty on 10/20/2012 11:46:40 AM , Rating: 5
This isn't in any way a new idea. I've been telling this exact same story (including the complete destruction of Earth and Theia) to my astronomy students for years.


At a later point, Earth's rotation could have slowed due to the moon and sun aligning in a way that changed Earth's orbit.

Yeah, no. The shape and size of the orbit have nothing to do with the rotational period of the Earth. The effect you want is called tidal braking and it doesn't have anything to do with the alignment of the Earth, Sun, and Moon, either, it only requires that you have orbiting bodies with dissimilar rotational periods.

I understand that you probably have a quota on articles to write, but you really need to understand the material before you write, first.

RE: *sigh*
By DanNeely on 10/20/2012 2:15:52 PM , Rating: 2
From better quality reporting I saw a week ago; what's new is that researchers have found an additional mechanism to drain angular momentum from the Earth-Moon system. As a result the proto-Earth could have been spinning faster when it was hit than previously believed. One of recent paper used the higher initial spin rate to get a more thorough mixing of the protoplanets mantles needed in order for the Earth-Moon isotope ratios to match as closely as they do. A second paper by a different group accomplished the same by colliding two protoplanets of approximately equal sizes.

I don't recall where I first read it. lists the names of the authors and the Journals they were published in so you (or anyone else was access) could read the actual papers being mangled here; and its article mentions everything I did except the additional spindown mechanism.

RE: *sigh*
By ET on 10/22/2012 7:35:14 AM , Rating: 2
Thanks. This makes more sense.

RE: *sigh*
By vol7ron on 10/20/2012 2:27:48 PM , Rating: 1
This isn't in any way a new idea. I've been telling this exact same story (including the complete destruction of Earth and Theia) to my astronomy students for years.

I hope you address it as that, a theory

RE: *sigh*
By Goty on 10/20/2012 3:00:11 PM , Rating: 3
Of course it's a theory. So is Newton's law of gravity, so is relativity. I don't think you really know the scientific meaning of the word.

RE: *sigh*
By Samus on 10/20/2012 10:09:23 PM , Rating: 1
Na, it's not a theory man. I was there when it happened, MAN.

RE: *sigh*
By wordsworm on 10/21/2012 11:58:26 AM , Rating: 1
The law of gravity is not a theory. It's a law. Relativity is a theory, which is why it's called the theory of relativity.

RE: *sigh*
By Goty on 10/21/2012 12:39:30 PM , Rating: 2
I'll go ahead an lump you in the group with the other guy. I guess gravity being a "law" explains why breaks down in regimes where relativity still functions and why relativity can predict things that Newton's law of gravity cannot (like the precession of Mercury's orbit or the bending of light around massive objects)? Yeah, that must be it.

If you know so little about the subject as to not even recognize that general relativity is a replacement and extension of Newton's law of gravity, you really shouldn't be commenting in this thread.

RE: *sigh*
By StormyKnight on 10/23/2012 1:01:55 AM , Rating: 2

RE: *sigh*
By delphinus100 on 10/21/2012 12:45:59 PM , Rating: 2
But that 'law' only describes what gravity does, not what it is.

Laypeople tend to use the word 'theory' in the way scientists use the word 'hypothesis.' One poses a hypothesis, tests it with experiment and/or observation, and theories are built on, or modified by, or invalidated by the results of those experiments or observations.

And no, we don't yet fully understand the actual nature of gravity, mostly because we can't yet reconcile General Relativity and Quantum Mechanics (both well-supported theories that describe certain aspects of the Universe in different, inconsistent ways) into a single theory.

RE: *sigh*
By KPOM1 on 10/21/2012 12:46:07 PM , Rating: 2
Is it a theory or a hypothesis?

RE: *sigh*
By Goty on 10/21/2012 2:36:30 PM , Rating: 3
Theory. General relativity has been rigorously tested and no contradictions have yet been observed.

RE: *sigh*
By JNo on 10/21/12, Rating: -1
RE: *sigh*
By Goty on 10/21/2012 11:44:49 PM , Rating: 5
Actually, none of these theories have been proven. That's the crux; to be scientific a hypothesis must be disprovable, so absolute proof is unobtainable.

As to the rest of your self-righteous ranting, since when is it wrong to expect a journalist to inform themselves on a subject before publishing or to exhibit self-control in abstaining from adding extraneous, made-up statements to an article instead of making a five minute visit to Wikipedia beforehand? Laziness is not an excuse for poor writing.

RE: *sigh*
By retrospooty on 10/20/2012 9:03:13 PM , Rating: 2
"This isn't in any way a new idea. I've been telling this exact same story (including the complete destruction of Earth and Theia) to my astronomy students for years."

Exactly... I have seen this all over the science channel for at least the last decade. Anything but new. Cool , but not new.

RE: *sigh*
By ShaolinSoccer on 10/21/2012 11:13:50 PM , Rating: 2
Kind of like Reddit. They recycle "old" stuff there constantly and get tons of upvotes for it... Gotta love teenagers...

RE: *sigh*
By Chemical Chris on 10/20/2012 10:04:06 PM , Rating: 2
I wish I still had it, but my grandfather (retired librarian) had a book from the late 1800's about astronomy. In it, it said that they once thought the moon was formed from a collision between two objects a long time ago (as we now believe); but that that theory had been discarded as nonsense and the earth instead trapped the moon by its gravity.
I love how the state of 'truth' changes over time!
(thats a good thing, btw, changing ones opinion based on new evidence/facts)

RE: *sigh*
By Goty on 10/21/2012 12:41:08 PM , Rating: 2
That would be awesome to have. The big difference between now and then (and why I'd say our claims today are much stronger) is that we have evidence of the composition of each body, whose similarity is best explained by the giant impact hypothesis.

RE: *sigh*
By maugrimtr on 10/22/2012 8:52:56 AM , Rating: 3
The "truth" doesn't change. All we have are hypothetical scenarios that could lead to the formation of the moon we have. The trick is finding one which fits all the observations and known composition of the moon so it graduate a little bit closer to "truth".

So the article above is a bit of a mess. We've known about the broad strokes for many decades - either we captured the moon or it formed in orbit from Earth debris, i.e. most likely from a collision with another planet. Capture seems improbable so collision is not the frontrunner. The new information provides a scenario where we end up with a moon closer to the composition we expect - that's why it's big news.

RE: *sigh*
By kattanna on 10/22/2012 10:56:07 AM , Rating: 2
I understand that you probably have a quota on articles to write, but you really need to understand the material before you write, first

sadly.. that statement can be made to much of what passes for "journalism" these days

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