Geology and Earth ScienceWhere did the Moon come from (part 1 - The Big Three) by Joe Leddy
Where did the Moon come from? (part 1 The Big Three)
Since the beginning of civilization man has been fascinated by the Moon. It has been worshiped,
feared, and studied. For centuries we have theorized how the Moon came to be.
The first modern scientific studies we conducted by Galileo in 1610, when he discovered that the light and dark spots were plains and mountains. Galileo was on the right path in his discoveries of how the Earth/Sun system worked, until the Church tried him for heresy and all published thoughts along these lines (at least within the influence of the Church) stopped.
Charles Darwins son George put the first theory of the origins of the Moon to gain some measure of acceptance forth. George Darwin theorized the Earth spun the Moon into existence. According to Darwin, the Earth in its infancy spun so rapidly that a chuck was pulled of an elongated Earth. Darwin initially put forth his theory in 1878. Four years later geologist Osmond Fisher added to the theory by stating the scar left behind from this fission was in the
Pacific Ocean. The Fission Theory was widely accepted well into the 20th century.
In 1909, some competition enters the Moon origins discussion. Thomas Jefferson Jackson See, an astronomer with quite possibly the most American name of all time, advocated the Capture Theory. According to See, the Moon was really a wandering planet that was captured by the Earths gravity.
There was still another theory that entered the fray. Edouard Roche, an astronomer advocated a co-accretion theory that the Earth and the Moon formed simultaneously from the same material that all of the planets formed from. This would come to be known as the Co-accretion Theory.
These theories were dubbed the Big Three, and were a source of much debate. Selenology, the study of the moons origins, really gained some footing after the Apollo missions (and corresponding Russian missions) brought over 800 pounds of lunar rock to study.
Studies of these rocks showed some remarkable similarities between the Earth and the Moon. Studies of the isotopes present in the rocks showed both bodies to be roughly 4.5 billion years old, and the quantity of stable oxygen isotopes showed a similarity in the distance both bodies formed from the Sun. The Earth and Moon were shown to be a system. This still does not tell us which of the Big Three was correct, if any.
The Fission Theory falls apart under study. It might explain the lack of a core in the Moon and the Moons similarity to the Earths Mantle, however it stops there. The physics behind the Fission Theory does not work. The speed at which the Earth would have had to been spinning is off the charts. Add that to the fact that the Pacific Basin is 70 million years old, not 4.5 billion and the theory is dead.
The Capture Theory also fails under a combined geological and physics based study. Geologically the chances that a planet developed elsewhere in the galaxy/solar system would have the same properties as the mantle, but no core, does not work. In addition the chances of an object the size of the Moon being captured by the Earth, at just the right angle and speed, are so small they are statistically impossible.
The Co-accretion Theory does not explain the lack of a core in the Moon. In addition, the chances that the Earth develops with all of the iron while the Moon has none make this theory very improbable.
If the Big Three are out, what's left? In part two of this post I'll look at a new theory that is leading the way "The Big Whack'.
1 Comments:
The moon, along with the rest of the universe is fascinating and in the beginning there was nothing but speculation of what it is or where it came from. Galileo discovered many things about the moon such as, the craters that are visible from earth. Galieo was more concerned with proving that the sun was and is the center of the universe while is son george was more concerned with how the moon came about. There were other astronomers that had their own theories of how they came about but in the end, all of them were fill with many gaps and were eventually overlooked.
The first theory is from George Galileo, who believed that during the beginning stages of the earth, it spun very rapidly, forcing a chunk to brake off. This is a very good theory considering the technology that was available. This reminds of the solar nebula theory, but except with the sun it’s the earth. Wouldn’t there be more than one moon? It’s hard to believe that if it as spinning that rapid more pieces of earth would have broke off and we would have multiple moons probably different in size and at different location away from earth because of gravity. Again this is a great theory considering the time period it was given in. with todays technology us to land on the moon and find out the earth is of different composition than the moon or at least in the wrong proportions, so this theory is wrong.
This next theory by Thomas Jackson Jefferson See, to me is the most ridiculous. Like it was noted, perfect conditions in space like gravity and angles working together to capture the moon is virtually and statistically impossible. I would not have forgotten about spiining theory to take over this one. It is a good attempt, but to me very unlikely. Instead of capturing the moon, I would think that moon could have impacted earth destroying because of it’s size.
I would have to agree with this article about the co-accretion being the best theory for the time period. This is like the spinning theory but given a more specific time zone, the accretion of earth and that both of these, the moon and earth were created at the same time. Again they are composed of different material or the proportions are off. There is no iron on the moon while there is an abundance on earth. The reason I like this one the best is that best describes why the moon has a small core.
In conclusion all of these theories have negatives and positives about them and I can see why there was a debate over which one of these is to be accepted. It is all about the way you look at the senerio and which one makes more sense. Again I am looking at these theories as a scientise/astronomers, who did not have the technology then as we do now. It is very weird that we know how most moons of there planets cam to exist and we still don’t know for sure how the earths moon came about. I guess it is up to the “Big
Whack Theory” to take over.
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