Quote:
The moon doesn't get a lot of action. Unless humans come along to muck things up, the lunar surface remains pretty much as it has been for hundreds of millions of years. But this rock managed to leave a trail in the regolith as recently as 50 million years ago. How did it manage that?
Trails have been made on the moon at various points in lunar history, but studies suggest that regolith buildup from micrometeorite impacts erases any evidence of movement over the course of tens of millions of years. According to current estimates, this trail, made by a boulder nine meters in diameter, would be a mere 50-100 million years old. That's pretty recent for movement on the moon, and the folks at the Lunar Reconnaissance Orbiter suggest the movement may be extralunar in origin. Perhaps the boulder was hit by a very small meteorite, knocking it from its post and sending it on a rare journey through the regolith.
http://io9.com/5884344/50-million-years-ago-this-boulder-rolled-across-the-moons-surface
CKA Uber 
