Something to think about. Joseph Smith said that the earth was formed from other broken up planets. Matter unorganized. Another thought I have had is that Adam may have been in the Garden of Eden for a long time before partaking of the fruit that made him mortal and started time as we know it. Also scientific theory is just that. Theory. For instance the Leaky's say modern man originated in the Odivai Gorge in Africa because they found the remains of Lucy, a according to them "missing Link". But there is in England plenty of evidence of modern man that dates to the same time period. They ignore that because it doesn't fit in with ther excepted ideas. Really I dont think anyone knows and the Lord hasn't revealed a difinitive answer. That doesent mean we shouldn't interest ourselve in such questions. Keep an open mind