The Moon hung close
Six-hour days and tides hundreds of metres high
See it on the timeline →In depth
The Moon probably formed some 20,000–30,000 km away, against 384,000 km today. Tidal friction transfers rotational energy from Earth to the Moon's orbit: the Moon spirals outward by 3.8 cm a year, while Earth's rotation slows by about 1.7 milliseconds per century. Devonian coral fossils record roughly 400 days in a year, exactly as the theory requires. The violent early tides washed continuously between sea and land, and have been proposed as a way of concentrating organic molecules in tidal pools.
For children
Just after the Moon formed it was far closer than today — it filled a large part of the sky. Earth spun so fast that a day lasted only about six hours, and the tides were enormous. The Moon is still moving away from us, at about the speed your fingernails grow.
Connects to
Part of Terra Saga — the story of Earth on a timeline. terrasaga.org