How the Moon formed: giant impact of Theia
A Mars-sized body called Theia hit Earth 4.5 billion years ago and debris formed the Moon.
The giant impact that made the Moon
About 4.5 billion years ago a Mars-sized body named Theia struck the young Earth at 10 kilometers per second. The collision vaporized rock and threw 70 percent of debris from Earth's mantle into orbit.
The debris ring clumped into the Moon in only 100 years, a blink in geology. The newborn Moon was 10 times closer at 38,000 kilometers and looked 20 times larger in the sky.
Why the Moon matters today
The Moon stabilizes Earth's tilt at 23.5 degrees, giving steady seasons. Without it models show chaotic wobbles of 60 degrees. Tides from the Moon also mixed early oceans where life evolved.
Laser mirrors left by Apollo show the Moon drifts 3.8 centimeters farther each year. Total eclipses will end in 600 million years when the Moon looks too small to cover the Sun.
- Impact 4.5 billion years ago
- Theia was Mars-sized, 6,000 km wide
- Moon formed in about 100 years
- Newborn Moon only 38,000 km away
- Moon drifts 3.8 cm farther yearly