The Bering Isthmus - Natural History Notebooks
Five hundred years ago, a Jesuit priest speculated that the Native American descendents of Adam and Eve migrated on foot to North America across a land connection located somewhere in the northwest. A century later, the Scandinavian navigator Vitus Bering charted the northwest coastline and the narrow body of water that separates Alaska from Siberia.
That 90-km wide (55 mi.) strait is now called the Bering Strait, and the long-vanished land connection, the Bering Isthmus. The connection—sometimes called a land bridge—and the land that encompassed it on both coasts are called Beringia.
This land connection existed several times during the Pleistocene Epoch. This was the latest glacial epoch (an ice age), and it began approximately 2 million years ago and ended around 10 000 years ago. The land connection formed because in glacial times, water gets locked up in snow and ice on the land in the form of massive ice sheets kilometres thick. Ocean levels drop as a consequence. When the ocean level dropped 100 m (300 ft.) during the last glacial episode, the relatively shallow shelf of land between Asia and North America was exposed, and the two continents were joined by a broad isthmus. The Bering Isthmus was submerged once again about 11 000 years ago, when the climate warmed, the glaciers melted and the ocean rose.
The Bering Isthmus formed the central part of Beringia, which at its peak was about 2700 km (1,700 mi.) across. It extended from the Kolyma River and Kamchatka peninsula in Siberia, through Alaska and Yukon at least to northern Banks Island in the Northwest Territories.
Beringia was mainly a steppe-like grassland occupied by plants and animals, many of which eventually spread into North America from Eurasia or, rarely, in the opposite direction. Many northern animals, such as caribou, moose, muskoxen, wolves and lemmings, arrived in North America via this route. So did mammoths, the giants of the Pleistocene.
The human hunters that ate these creatures followed them. Archaeological evidence suggests that people first occupied eastern Siberia about 35 000 years ago, and Yukon (Bluefish Caves, Old Crow and Dawson areas) about 25 000 to 30 000 years ago. Recently, genetic studies revealed that Natives in both South and North America share a unique genetic variant, one that proves their ancestors came from a single source. The only other place in the world this genetic marker has been found is eastern Siberia. Thus, the evidence is clear that the Bering Isthmus played an essential role in the human colonization of North America.
[Map: Russ Brooks].