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Various scientific theories regarding the origin of the moon have been considered as follows:<ref name="PSI">Planetary Science Institute: [http://www.psi.edu/projects/moon/moon.html The Origin of the Moon]</ref>

Various scientific theories regarding the origin of the moon have been considered as follows:<ref name="PSI">Planetary Science Institute: [http://www.psi.edu/projects/moon/moon.html The Origin of the Moon]</ref>

#The Moon formed in an orbit around Earth at the same time that Earth formed.

*The Moon formed in an orbit around Earth at the same time that Earth formed.

##This idea was discarded when it was discovered that the moon has proportionally far less iron in it than the Earth.

**This idea was discarded when it was discovered that the moon has proportionally far less iron in it than the Earth.

#The Moon formed in a part of the solar system that was low in iron, and was later captured into an orbit arount the Earth.

 

##This failed upon examination of lunar rocks, which exhibit the same oxygen isotope composition as the Earth, unlike rocks known to come from other sources in the solar system, e.g. Mars.

*The Moon formed in a part of the solar system that was low in iron, and was later captured into an orbit arount the Earth.

#The Earth was originally spinning so fast that it spun off a fragment of lower density (iron-poor) material which became the Moon.

**This failed upon examination of lunar rocks, which exhibit the same oxygen isotope composition as the Earth, unlike rocks known to come from other sources in the solar system, e.g. Mars.

##This solves the isotopic similarity and the relative lack of iron, but an analysis of the total angular momentum and energy involved ruled out this possibility.

 

#An impact with a large planetesimal (asteroid-like body) released a great quantity of debris into orbit, a portion of which collected under the influence of gravity. This theory is the currently accepted scientific explanation of the origin of the Moon as it is able to explain the facts which contradicted earlier ideas:

*The Earth was originally spinning so fast that it spun off a fragment of lower density (iron-poor) material which became the Moon.

##The impact of the planetesimal happened relatively late in the earth's formation, which would explain (among other things) the lack of iron: By the time of the impact, the Earth's iron had already sunk deeper towards the core. Thus, the debris that eventually formed the Moon came from the iron-depleted mantle.  Most of the planetesimal itself would have sunk into the earth's core.

**This solves the isotopic similarity and the relative lack of iron, but an analysis of the total angular momentum and energy involved ruled out this possibility.

##Since the Moon was created from debris blown out of the Earth, the Earth and the Moon have the same oxygen isotope composition.

 

##Enough energy would be released from a major collision such as this to put a substantial mass of the earth's crust into orbit.

*An impact with a large planetesimal (asteroid-like body) released a great quantity of debris into orbit, a portion of which collected under the influence of gravity. This theory is the currently accepted scientific explanation of the origin of the Moon as it is able to explain the facts which contradicted earlier ideas:

**The impact of the planetesimal happened relatively late in the earth's formation, which would explain (among other things) the lack of iron: By the time of the impact, the Earth's iron had already sunk deeper towards the core. Thus, the debris that eventually formed the Moon came from the iron-depleted mantle.  Most of the planetesimal itself would have sunk into the earth's core.

**Since the Moon was created from debris blown out of the Earth, the Earth and the Moon have the same oxygen isotope composition.

**Enough energy would be released from a major collision such as this to put a substantial mass of the earth's crust into orbit.

== Reference ==

== Reference ==

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