Research recently revealed that the Earth and Moon had a much closer relationship about 2.5 billion years ago: The Moon orbited nearer our planet, and Earth’s spin was much faster.
“It’s possible to get this information about the Earth-Moon dynamics, and also the solar system, by looking at old rocks,” says Margriet Lantink, a post-doctoral earth scientist at the University of Wisconsin-Madison and lead author of the latest study. “It’s really cool.”
Of course, researchers couldn’t say for sure the distance between even the modern-day Earth and the Moon until we first reached the satellite half a century ago. At that time, astronauts put reflectors on the Moon that could be seen from Earth. By monitoring their distance over time, scientists determined that the Moon is moving away from us at a rate of about 3.8 centimeters per year on average — due to a gradual decrease in tidal energy that decelerates the Earth’s spin on its axis.
