Variation in thickness of the lunar crust may have been caused by early chemical differentiation of the crust soon after the Moon was locked to Earth by gravitational attraction.
(Variation in thickness of the lunar crust; may have been caused soon; T:after the Moon was locked to Earth by gravitational attraction) (the Moon; was locked; by gravitational attraction)
Variation in thickness of the lunar crust the Moon
may have been caused soon was locked
T:after the Moon was locked to Earth by gravitational attraction
by gravitational attraction