The leading theory for the formation of the Moon is the Giant-Impact Hypothesis. This theory proposes that a Mars-sized object, named Theia, collided with the early Earth about 4.5 billion years ago.

Here's what happened:

1. Collision: Theia, a protoplanet, struck the young Earth at a glancing blow. The impact was incredibly powerful, releasing immense energy.

2. Ejection: The impact vaporized a massive amount of material from both Theia and Earth, sending it into orbit around the Earth.

3. Accretion: The ejected material, composed of rock and gas, started to clump together due to gravity. Over time, these clumps coalesced into the Moon.

Evidence supporting the Giant-Impact Hypothesis:

* Moon's composition: The Moon's composition is similar to Earth's mantle, supporting the idea that it formed from Earth's material.

* Moon's orbit: The Moon's orbit is tilted and eccentric, which is unusual for a natural satellite. This could be explained by the impact's chaotic energy.

* Earth's tilt: The Earth's axial tilt is believed to have been caused by the impact of Theia.

While the Giant-Impact Hypothesis is widely accepted, it's still a complex theory, and there are ongoing research efforts to refine it.