I've come to understand that many things happened to the earth at the Fall, having to do with God's cursing it for our sake, and that includes the bombardment by meteors that is evident on the moon but not evident on earth -- probably because the Flood erased the craters (I had thought that bombardment must have occurred during the Flood but I believe now it was part of the cursing of the creation with the Fall), and this cursing also includes the "ice age" which explains the development of the wooly mammoth too, as well as that beast's huge tusks and the sabre-toothed tiger and the like for the purpose of defense or killing prey.