The first humans to populate America are thought to have migrated from Asia, trough the Bering Straits during the last glacial era. The planet's temperature lowered to 1.5 to 5.5 °F in average, causing water from oceans, lakes, rivers to froze; as the oceans froze, the sea level between Asia and America lowered, allowing people (and animals) to cross from one continent to the other.