Exanding Earth?
The lost tribe of Israel reference is of just one group Mormons claimed settled on the American continent. That one was way too early for that, assuming the 12000 year old numbers are correct. What you are referring to is what we (yes I am LDS) believe happened in 600 bc, that is a group of people from Jerusalem, from the tribe of Joseph, referenced here:
http://scriptures.lds.org/en/1_ne/1
Much earlier, we believe another group came from the scattering at the Tower of Babel, referenced here:
http://scriptures.lds.org/ether/1
Even earlier, we believe that civilization began on this continent, and continued here, from Adam to the flood. It was when the earth was divided right after Noah in the days of Peleg that we believe there was a separation between the old and new worlds, referenced here:
http://scriptures.lds.org/en/gen/10/25#25
I’m not here to argue my faith, I don't have the time I used to. I am just setting the record straight as to our beliefs about the timeline of some migrations here.
All the best.
Exanding Earth?