The literal interpretation of Genesis isn't just bad on scientific grounds, but it is also bad on theological grounds. Genesis, like the rest of the Old Testament, is a rich, interwoven tapestry, each containing many, many ancient voices singing out their praises for Yahweh, Elohim, and His kingdom. We have here recounted the folkloric traditions of the Israelites, their stories of origination and a narrative of their struggles with the divine presence.
If one reads Genesis as literal truth, then one misses the point entirely. The first few chapters are a story of a movement from some naive, remembered past, a golden age of prehistory, in which some (if not all) of the ancestors of the Israelites apparently occupied an area in what was to become southern Mesopotamia (which is the location indicated for Eden in Genesis chapter 2.)
Having overcome that naive existence, and wandering forth into what would have seemed a more civilised era, is represented in the eating of the apple from the tree of knowledge of good and evil.
It is this advancement of knowledge which simultaneously brings them out of a golden era of naivety and into the more modern era. When the culture diverts from that naive golden age, with the advancement of knowledge, a severe price is paid -- one can never return to the garden.
Lessons have been learned which cannot be undone. This is represented with the placement of cherubim (mythical creatures which are part eagle, lion, and human) and a flaming sword, to gaurd Eden from ever being entered again. This is not meant as a literal history, but it is meant to contain deep Truths. It disheartens me to see that some of the people who hold this book so highly are so woefully ignorant of its content, and the lessons that may be gleaned from it.