how astronomers came up with the theory that the moon is a piece of a super-planet that earth was once part of or is a piece of something the earth was struck by

Question

how astronomers came up with the theory that the moon is a piece of a super-planet that earth was once part of or is a piece of something the earth was struck by

In: Earth Science

Answer 1

[Giant Impact Hypothesis](https://en.wikipedia.org/wiki/Giant-impact_hypothesis)

Paraphrased for simplicity

About 4.5 billion years ago a Mars sized planet (Theia) hit the Earth. Supporting evidence:

* Earth’s Spin and Moon’s Orbit have similar orientations
* Earth-Moon System has high angular momentum
* The moon was once molten to an unknown depth
* The moon has a small iron core
* Moon is depleted of volatile elements compared to Earth
* Evidence of similar events in other star systems
* Giant collisions consistent with leading theory for formation of the Solar System
* Lunar and Earth rock similarities imply a common origin

This evidence makes an impact theory reasonable.