Sir George Darwin:
Sir George Darwin, an English astronomer and mathematician, proposed the concept of the earth and the moon forming a single rapidly rotating body to form the moon. He was the son of Charles Darwin, the renowned naturalist. Sir George Darwin made significant contributions to the field of celestial mechanics and the study of the evolution of the Earth-Moon system.

The Concept:
According to Sir George Darwin's concept, the moon was formed as a result of a giant impact between the early Earth and a Mars-sized celestial body named Theia. This impact caused the ejection of a large amount of material into space, which eventually accreted to form the moon.

Rapid Rotation and Tidal Forces:
Darwin proposed that in the early stages of the Earth-Moon system, the Earth and the moon were much closer to each other than they are today. The Earth was rotating much faster, completing a day in just a few hours. The gravitational forces between the Earth and the moon caused tidal bulges to form on both bodies.

Transfer of Angular Momentum:
The tidal bulges on the Earth and the moon created a transfer of angular momentum between the two bodies. This transfer of angular momentum caused the Earth's rotation to slow down and the moon to move away from the Earth. As a result, the moon's orbit gradually expanded over billions of years.

Formation of Moon:
According to Darwin's concept, as the Earth's rotation slowed down, the tidal bulges on the Earth became more pronounced. Eventually, the tidal forces and the rapid rotation of the Earth caused the material in the Earth's equatorial region to be pulled away and form a disk-shaped structure. This disk eventually accreted to form the moon.

Evidence:
Darwin's concept is supported by various lines of evidence, including the similarities in the isotopic composition of the Earth and the moon, the moon's synchronous rotation, and the presence of large impact basins on the moon's surface.

Conclusion:
In conclusion, Sir George Darwin proposed the concept of the earth and the moon forming a single rapidly rotating body to form the moon. His concept explains the formation of the moon through a giant impact between the early Earth and a celestial body. This concept is supported by various lines of evidence and has contributed significantly to our understanding of the evolution of the Earth-Moon system.