Scenario: Mars Colonization

Hundreds of Thousands of years before AD, the first Human ship was sent to Mars. Years later, the first Humans on Mars Found that Mars had a very habitable underground. With plant life and Animal life of all kinds. Fish-like creatures in the seas, Primate- like animals and other Earth-like species. Including A primitive Human/Monkey species. A man and a women where sent to Mars, one of each gender only. The spread like a wildfire. Soon the underground of Mars was completely Civilized by Humans.They had reached a year 2000 A.D. Tech. By the time they had achieved Planet-to Planet Comm, they had found out from a few survivors of a "War that had utterly reduced the Human Species on Earth down to a few Barbarians wearing bear skins" That not only the Earthlings had beaten and battered each other down to the primitive stage, that they had turned the all of the Equator of the Earth into a vast desert. Millennia later, The humans had re-formed themselves into their current stage.