Question: Global sea levels would have been at their lowest during the last global glacial maximum. Just when was that?
Answer: Perhaps as early as 23,000 BC or as late as 19,000 BC. A couple of adjustments have had to be made to the technique of radio carbon dating during the late 20th century, in order to calibrate it for greater accuracy. One adjustment was made utilizing tree ring counts-- but this measure could only help calibrate carbon dating back to 10,000 years in the past. A second correction to increase carbon dating accuracy beyond 10,000 years came from sea coral. Around 1990 the new calibration placed the last global glacial maximum at around 19,000 BC, where previous estimates had placed it at 16,000 BC.
|-- OF TIME AND THE CORAL - AND OTHER THINGS, TOO From Science Frontiers #71, SEP-OCT 1990 by William R. Corliss, citing Richard A. Kerr; "From One Coral Many Findings Blossom," Science, 248: 1314, 1990|
Still later, possibly more accurate estimates came from the National Oceanic and Atmospheric Administration and the National Science Foundation in 1998, to place the global maximum at 23,000 BC.
|-- "OLDEST ICE CORE FROM THE TROPICS RECOVERED, NEW ICE AGE EVIDENCE" from a project supported by the National Oceanic and Atmospheric Administration and the National Science Foundation, 12-3-98|
It seems however that circa 1999/2000 many journalistic and even some scientific sources continued to use the older, likely obsolete estimates of the glacial maximum, of around 18,000 BC to 16,000 BC. It appears the prime reasons are their reliance on outdated references, the relatively recent adjustments to the dates, and the general obscurity of the topic itself. Therefore I am here assuming the maximum to have occured around 23,000 BC- 19,000 BC, unless some new evidence to the contrary comes to light.
Keeping in mind many journalists' and even some scientists' possible continued reliance on outdated estimates for the maximum, I will often compensate for this likely error in my own speculations.
Some of the links on this search list may be helpful in visualizing vast regions of land submerged circa the 20th century but exposed as dry land around 23,000 BC.
23,000 BC was the last glacial maximum of the most recent Ice Age.
Ice sheets up to 10,000 feet thick reach as far south as near the vicinity of London England. The Earth boasts considerably more dry land now than it will circa 2000 AD, as the Ice Age has lowered the oceans even as it created the great ice sheets. The ice production itself also extends the mobility of land creatures like man via seasonal sea ice (at least in some cases).
In western europe, men can literally walk from France to the British Isles. But much of this area is similar to 20th century arctic tundra.
The land bridge between Asia and Alaska is at minimum around 700 miles wide, complemented by possible seasonal sea ice stretching some 700 miles beyond that in each of the north and south directions (for a potentially walkable bridge between continents ranging from some 700 to 2100 miles wide, depending on the season).
Note that 23,000 BC represents the glacial maximum-- which means although land bridges like the Bering were at their widest and most dry around 23,000 BC, they were likely passable for lengthy periods both before and after this time. How large a timespan are we talking about here? 31,000 BC through 8,500 BC to 7,500 BC. Or around 23,000 years.
|Sources include altitude maps of North America, Europe, and Asia, and depth maps of the Pacific Ocean floor and Atlantic Ocean floor, from the Concise Columbia Encyclopedia, Second Edition, 1989, Columbia University Press, as well as the Bartholomew World Physical map, HarperCollinsPublishers, 1992|
Well, it appears the Bering land bridge was sufficiently submerged by around 8,000 BC to cut off most foot travel between North America and Asia, and perhaps cause a stunningly rapid expansion into South America as a byproduct (the expansion seemed to have occured in 1000 years or less, judging from the sudden extinctions of megafauna on both continents).
The Bering land bridge may have been dry as recently as 9,000 BC, but its vegetation was inadequate to support grazing animals of substantial size.
-- Beringia Land Bridge Lasted Until 11,000 Years Ago, 11/26/96, Anthropology News Briefs ["http://realindy.com/anthronews.htm"]
-- "Traces of our Forebears", National Geographic, October 1988
-- "OLDEST ICE CORE FROM THE TROPICS RECOVERED, NEW ICE AGE EVIDENCE" from a project supported by the National Oceanic and Atmospheric Administration and the National Science Foundation, 12-3-98
The great migration of humanity across the land bridge is stymied somewhat on the american side by the fearsome great bears there for a time, for which the migrating land-based peoples have no adequate weapons for defense. Only towards the end of this period do these circumstances change dramatically, as increasing numbers and better cooperation and weapons among the human invaders serve to overcome the physical advantages of the bears and other large north american predators. Climate changes may also be aiding humanity by way of changing the habitats of large predators in ways which reduce their numbers.
Another obstacle to migrations into the heart of North America were the immense ice sheets which acted as vast inhospitable deserts between much of the Yukon/Alaska and the rest of North America. There were likely few willing to brave these icy deserts and the fearsome giant bears, to see what lay beyond. On the flip side, the northwestern Yukon was a pretty nice place to live for quite some time around now (23,500+ BC-8,500 BC), offering a wealth of food for those living there. Thus, the population in the region may have swelled for millennia before any large movements to the south were undertaken (though coastal expeditions likely conitnued unbroken during this time).
|-- "First North Americans Had Chance To Be Avid Birders", 21 APRIL 1999, Canadian Museum of Nature /Museum of Civilization, Jacob Berkowitz firstname.lastname@example.org, Rachael M. Duplisea, email@example.com|