Human "settlement" does not necessarily have to be continuous; settled areas in some cases become depopulated due to environmental conditions, such as glacial periods or the Toba volcanic eruption. Early "Homo sapiens" migrated out of Africa from as early as 270,000 years ago, although these early migrations may have died out and permanent Homo sapiens presence outside of Africa may not have been established until about 70-50,000 years ago.