Giant impact hypothesis
Also called: Big splat · Topic: Origin and Evolution of the Earth and the Solar System · NCERT: Class 11, Ch 2 "The Origin and Evolution of the Earth"
Meaning
The giant impact hypothesis is the leading explanation of how the Moon formed. A Mars-sized body called Theia hit the young Earth about 4.5 billion years ago. The debris thrown out by the crash came together to form the Moon. NCERT notes that the impact also heated the Earth further. Older ideas, such as fission (the Moon splitting off from the Earth), capture and forming side by side, have been set aside.
Example
Moon rocks brought back by the Apollo missions match the Earth's mantle in their oxygen isotopes (different forms of oxygen atoms). The Moon also has only a small iron core. India's Chandrayaan-3 landed near the lunar south pole on 23 August 2023, and lunar missions like it help test this story.
Don't confuse with
- Capture hypothesis: this older idea said the Earth's gravity trapped a Moon that had formed somewhere else. The matching oxygen isotopes go against it.