what evedence supports the current theory about our moon's orgin?

Answer 1

A brief summary off the top of my head:

Three theories were proposed early on. The Moon was spun off the Earth, the Moon formed near the Earth, or the Moon formed elsewhere and was captured by the Earth. The first was quickly discarded because no-one could produce a model that allowed the earth to spin fast enough to have a great chunk of itself spontaneously flung out. The Apollo lunar missions brought back rock and soil samples for analysis.

1: The lunar rocks show a similar elemental composition to rocks from Earth, suggesting they formed in the same part of the solar system (elemental composition is a bit like an address label; different areas of the solar system have different amounts of varying elements).

2: Oxygen isotope ratios are almost identical to Earths, also supporting the idea that it formed around here.

3: The moon is less dense than Earth, suggesting a different composition overall. Earth has a dense core of iron. The moon's overall density is almost the same as the rocky crust and mantle section of the Earth, suggesting it lacks an iron core. If it formed at the same time (as radioisotope aging of the rocks suggests it did) then it should have the same proportion of iron in it as Earth does overall. Apparently it doesn't.

4: A type of rock called Anorthosite was found on the Moon. It's the oldest rock brought back and is believed to be part of the original crust. Geologists believe it could only have formed if the crust was molten at one time, but the Moon is too small to have been that hot if it formed by aggregation of loose material as Earth did.

5: There is no water whatsoever in moonrock. Not even chemically bound into the rock itself.

So, the Moon was definitely formed around when the Earth was in the same general area, but has a different density and an odd crust that suggests it must have been molten.

The giant impact theory was proposed to explain these inconsistencies. A body the size of Mars collided with the Earthearly in its development. Debris was flung off and some coalesced to form a Moon. The reason for the different density is that the Earth had already differentiated by that time into the core and mantle layers, with the heavier elements at the centre and the lighter ones around the outside. The debris flung off was therefore composed entirely of the stuff that now makes up the mantle of the Earth, hence the Moon is effectively a big chunk of the outer layers of the Earth. The heat of the collision would have driven out the water from the debris that was ejected, hence the lack of water in the moonrocks.

Hope that helps

Answer 2

what is it
and theories about space don't usually have to much evidence behind them if any at all