Collision With Earth's "Little Sister" Created the Moon

astroengine writes The primordial planet believed to have smashed into baby Earth, creating a cloud of debris that eventually formed into the moon, was chemically a near-match to Earth, a new study shows. The finding, reported in this week's Nature, helps resolve a long-standing puzzle about why Earth and the moon are nearly twins in terms of composition. Computer models show that most of the material that formed the moon would have come from the shattered impactor, a planetary body referred to as Theia, which should have a slightly different isotopic makeup than Earth.

Comments

Another explanation

[Tablizer]

What about this explanation: a planetoid smashed into early Earth and split Earth into two. The two halves eventually smashed back together, but created the moon in the process. One "half" may have mixed more with the collider than the other due to the angle of impact, creating the slightly different isotopes in the parts of it that became the moon.

Re:So how rare is this occurance?

[kenwd0elq]

Our substantial magnetic field may be due to the merging of the iron cores of the Proto-Earth and Theia. Earth is the most dense planet in the solar system, and from what we know of Mars and Venus, we suspect that our iron core is far larger than the other terrestrial planets.

Venus has a super-thick poisonous atmosphere; it's at least possible that our large Moon has, over a period of 4+ billion years, "skimmed away" enough of our atmosphere to have protected the Earth from a similar fate.

Of course, we only think that our atmosphere is right because we evolved here, in this atmosphere; if the atmosphere had been different, we would have evolved differently, and (had intelligent life developed at all) we'd think that THAT was the right sort of atmosphere.