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

Re:Another explanation

[confused one]

Orbit is too circular for that solution to work.

Re:Earth's atmosphere was different

[TapeCutter]

Causing an environmental catastrophe at the time.

Yep, oxygen build up was a disaster for the cyanobacteria that created it and had reigned Earth for 3+ billion years. On the plus side the free oxygen enabled collagen to form, which is the substance that holds single cells together in multi-cellular organisms. We call that transition "The Cambrian explosion". The collision we are talking about occurred 3.5 billions years before the Cambrian explosion.