  The lunar farside highlands problem refers to the curious and unexplained
fact that the farside lunar crust is thicker, on average, than the nearside
crust. Here we recognize the crucial influence of Earthshine, and propose that
it naturally explains this hemispheric dichotomy. Since the accreting Moon
rapidly achieved synchronous rotation, a surface and atmospheric thermal
gradient was imposed by the proximity of the hot, post-Giant-Impact Earth. This
gradient guided condensation of atmospheric and accreting material,
preferentially depositing crust-forming refractories on the cooler farside,
resulting in a primordial bulk chemical inhomogeneity that seeded the crustal
asymmetry. Our model provides a causal solution to the lunar highlands problem:
the thermal gradient created by Earthshine produced the chemical gradient
responsible for the crust thickness dichotomy that defines the lunar highlands.
