Changes

==Giant Impact Hypothesis==

==Giant Impact Hypothesis==

===Development===

===Development===

In 1974, William Hartmann and Donald Davis suggested the hypothesis that a planetoid (early on estimed to be the size of Mars) impacted with a relatively young Earth and blasted mantle material into on orbit, where it would eventually form the Moon. This model also became known as the "Big Whack" hypothesis. Around the same time, Alastair Cameron and William Ward had come to a similar conclusion. However, their research had been motivated by studies of the angular momentum.<ref name="PSI"/><ref name="Nova2">PBS NOVA: "To the Moon - Origins" [http://www.pbs.org/wgbh/nova/tothemoon/origins2.html (Page 2)]</ref>

In 1974, William Hartmann and Donald Davis suggested the hypothesis that a planetoid, estimated in some calculations to be the size of Mars - impacted with a relatively young Earth and blasted mantle material into orbit, where this would eventually form the Moon. This model also became known as the "Big Whack" hypothesis. Around the same time, Alastair Cameron and William Ward had come to a similar conclusion. However, their research had been motivated by studies of the combined angular momentum of the Earth and Moon.<ref name="PSI"/><ref name="Nova2">PBS NOVA: "To the Moon - Origins" [http://www.pbs.org/wgbh/nova/tothemoon/origins2.html (Page 2)]</ref>

Initially, the the hypothesis was rejected with the claim that a catastrophic event of such a dimension and with such results seemed extremely unlikely.<ref name="Nova2"/> Still, it explained the lack of iron, the oxygen isotope issue and the angular momentum.

Initially, the hypothesis was rejected with the claim that a catastrophic event of such a dimension and with such drastic results seemed extremely unlikely.<ref name="Nova2"/> Still, it explained the lack of iron, the oxygen isotope issue and the angular momentum.

Ten years later, the Giant Impact Hypothesis emerged as the leading model after a conference about the Moon origin in Kona, Hawaii. In the 1990s, Robin Canup picked up the research and created simulations to determine possible scenarios that might explain the formation of the Moon.<ref name="PSI"/><ref name="Nova2"/>

Ten years later, the Giant Impact Hypothesis emerged as the leading model after a conference about Moon origin in Kona, Hawaii. In the 1990s, Robin Canup picked up the research and created simulations to determine possible scenarios that might explain the formation of the Moon.<ref name="PSI"/><ref name="Nova2"/>

Canup initially came to the conclusion that much of the material blasted off by a "Big Whack" would either fall back to Earth or fly off into space, thus requiring a very large impactor (one with a factor of two or three in mass, compared to the initial assumptions). However, later on, improved computer simulations suggested that the size of the impactor may have been smaller after all, thus leaving all calculations regarding mass and momentum intact.<ref name="PSI"/><ref name="SciAm">Scientific American: [http://www.sciam.com/article.cfm?chanID=sa006&colID=5&articleID=000A90B0-C919-1C6E-84A9809EC588EF21 "Earth-Shattering Theory"]</ref>

Canup initially came to the conclusion that much of the material blasted off by a "Big Whack" would either fall back to Earth or fly off into space, thus requiring a very large impactor, one two or three times larger than initially envisaged. However, later on, improved computer simulations suggested that the size of the impactor might not have to be so large after all, thus leaving all calculations regarding mass and momentum intact.<ref name="PSI"/><ref name="SciAm">Scientific American: [http://www.sciam.com/article.cfm?chanID=sa006&colID=5&articleID=000A90B0-C919-1C6E-84A9809EC588EF21 "Earth-Shattering Theory"]</ref>

===Criticism===

===Criticism===