[ jī′ənt ] A theory that explains the origins of Earth’s moon, postulating that an asteroid roughly the size of Mars impacted the Earth during its formation. This impact resulted in rocky surface material being blown outward from the Earth, some of which accreted to form the Moon.

What are the major points of the giant impact theory?

The giant-impact hypothesis, sometimes called the Big Splash, or the Theia Impact, suggests that the Moon formed from the ejecta of a collision between the proto-Earth and a Mars-sized planet, approximately 4.5 billion years ago, in the Hadean eon (about 20 to 100 million years after the Solar System coalesced).

What is the problem with the giant impact hypothesis?

This hypothesis is implausible in its present form because: (1) it possesses a low intrinsic dynamical probability; (2) the collision would have melted and differentiated the Earth causing geochemical signatures quite different to those actually observed; and (3) the collision mechanics cause the Moon to be derived …