Bering Land Bridge is as much a part of America's cultural heritage as Yellowstone or Yosemite, if not more so. The distance across the Bering Strait from Siberia to Alaska's Seward Peninsula — also known as Beringia — is approximately 55 miles, and for several periods during the Pleistocene Ice Ages the trip could be made entirely on land instead of water. "Bridge" is really a misnomer, for the landmass ranged up to 1,000 miles wide. During additional periods the passage from Siberia to North America could also have been made by small watercraft bumping along coastlines.

Most of the Aleutian island chain became a peninsula, with its islands also nearly linked the continents. As glaciers fluctuated, much of Beringia — even inland of today's Alaska coast — often stood free of ice and would have been habitable by humans.

Just when humans first traversed Beringia is subject to less agreement. The Pleistocene epoch began 1.6 million years ago and ended only 10,000 years ago after a final onslaught of ice known as the late Wisconsinan glaciation. It is theoretically possible for people to have entered North America from Asia at repeated intervals between 40,000 and 13,000 years ago. Artifacts suggest that people lived in both North and South America by some 12,000 years ago; by that time waters of the Bering Strait had become a significant barrier again. However, similarities between peoples of coastal Siberia and coastal Alaska show that the Bering Strait did not prevent contact between their cultures. Similar languages, shared spiritual practices, hunting tool and traditional dwelling similarities, distinctive fish cleaning methods, and meat preservation by fermentation are but a few examples ethnologists cite.

Continental Glaciation

Grasping the magnitude of Ice Age glaciation is possible today only on Earth's two extant polar ice sheets in Greenland and Antarctica. During the final Ice Age push vast ice sheets up to nearly two miles thick burdened much of North America. Because the amount of water in Earth's hydrosphere is constant, the great ice sheets' hoarding of global waters caused sea levels to fall significantly. As a result, landmasses grew dramatically where continental shelves slope gradually, as they do here in the Bering Strait.

Continental shelves are the shallow submarine plains that border many continents and typically end in steep slopes to an oceanic abyss. Where a wide continental shelf slopes gradually, a small drop in sea level can increase shoreline areas greatly. At Beringia, a sea level drop of approximately 300 feet during the Wisconsinan glacial period revealed a relatively flat, low-lying stretch of continental plain linking North America to Asia — the Bering Land Bridge.

Sea level now rises an average of one foot per century because global warming is melting the great polar ice masses of the Arctic and Antarctica. The greenhouse effect and loss of stratospheric ozone may have increased the rate of global warming recently. Many clues to this intriguing puzzle about how and when humans first peopled the Americas undoubtedly lie under water now.

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