Throughout history, the Moon has served many roles such as a basis for calendars, an ultimate destination, and the source of tides. More recently it has also been used to better understand our planet's past, as it is Earth's oldest and closest companion. Researchers at NASA and MIT have recently used the Gravity Recovery and Interior Laboratory (GRAIL) mission to probe that past and have been quite surprised by the results.
Depending on where you live on Earth, you may have a level of dislike for plate tectonics, as this is what causes earthquakes, but without plate tectonics to heal the crust and recycle our atmosphere, life likely could never have developed here. The Moon though has no plate tectonics, so every wound its crust has ever suffered has left a permanent scar, and GRAIL has found far more of those scars than expected. By precisely measuring the distance between the two GRAIL satellites it is possible to map the gravity of the moon, and by subtracting the gravity of mountains and other topographic features, the gravity map of just the crust is left.
Without a trained eye or understanding of geology it is apparent the Moon has been battered throughout its life as 98% of the crust is fragmented. What happened to the Moon likely happened to the Earth as well, in its younger years, but plate tectonics removed the evidence. Now that evidence can be incorporated into planetary science theories describing the younger ages of planets.