Early Bombardment

Early bombardment of the Moon by planetesimals, from geocentric and heliocentric orbits, are the possible cause of the lunar crustal thickness asymmetries. The Earth’s presence also causes the Moon to be bombarded non-uniformly. A very early, yet intense bombardment like this could have redistributed lunar crustal materials, thinning certain lunar regions. This period is suggested to be < 3.9 Gyr ago.