Many of the lunar mountain ranges actually mark ancient crater rims. Unlike Earth, none of these features were formed by volcanism or by plate tectonic collisions. Rills and ridges that cross the lunar surface show evidence of surface contractions due to cooling of the rocky material of the lunar surface. The nature of the Moon's surface leads astronomers to the conclusion that it is basically original and was modified only by cratering and lava flows. By analyzing the Moon's physical features, therefore, we can deduce the early history of our solar system.