The Bering Land Bridge (image) University of Utah Caption This map shows the outlines of modern Siberia (left) and Alaska (right) with dashed lines. The broader area in darker green (now covered by ocean) represents the Bering land bridge near the end of the last glacial maximum, a period that lasted from 28,000 to 18,000 years ago when sea levels were low and ice sheets extended south into what is now the northern part of the lower 48 states. University of Utah anthropologist Dennis O'Rourke argues in the Feb. 28 issue of the journal Science that the ancestors of Native Americans migrated from Asia onto the Bering land bridge or "Beringia" some 25,000 years ago and spent 10,000 years there until they began moving into the Americas 15,000 years ago as the ice sheets melted. Credit Wlliam Manley, Institute of Arctic and Alpine Research, University of Colorado. Usage Restrictions Credit required. Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.