There is evidence that there may have been some stands of spruce trees in these regions too in some protected microhabitats, where temperatures were milder than the regions around. The presence of a particular group of beetle species that live in shrub tundra habitats today in Alaska, and are associated with a specific range of temperatures, also supports the idea that the area was a refuge for both flora and fauna.
This kind of vegetation would not have supported the large, grazing animals — woolly mammoth, woolly rhino, Pleistocene horses, camels, and bison. These animals lived on the vegetation of the steppe-tundra which dominated the interior of Alaska and the Yukon, as well as interior regions of northeast Siberia. This shrub tundra would have supported elk, perhaps some bighorn sheep, and small mammals.
But it had the one resource people needed most to keep warm: wood. The wood and bark of dwarf shrubs would have been used to start fires that burned large mammal bones. And there is evidence from archaeological sites that people burned bones as fuel — the charred remains of leg bones have been found in many ancient hearths. It is the heat from these fires that kept these intrepid hunter-gatherers alive through the bitter cold of Arctic winter nights. Escape to America The last ice age ended and the land bridge began to disappear beneath the sea, some 13, years ago.
The distance across the Bering Strait from Siberia to Alaska's Seward Peninsula is approximately 55 miles, and for several periods during the Pleistocene Ice Ages the trip could be made entirely on land instead of water.
During additional periods, the passage from Siberia to North America could also have been made by small watercraft moving along coastlines. Bering Land Bridge National Preserve commemorates this prehistoric peopling of the Americas from Asia some 13, or more years ago. It also preserves important future clues in this great detective story regarding human presence in the Americas.
During the final Ice Age Push, vast ice sheets up to nearly two miles thick burdened much of America. Because the amount of water in Earth's hydrospere is constant, the great ice sheets' hoarding of global waters caused sea levels to fall significantly. As a result, land masses grew dramatically where continental shelves slope gradually, as they do 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. During the time of the Bering Land Bridge, a sea level drop of approximately feet during the Wisconsinan glacial period revealed a relatively flat, low-lying stretch of continental plain linking North America to Asia. But it was still speckled with rivers and streams.
Bond's map shows that it likely had a number of large lakes. These environments helped megafauna — animals heavier than lbs. This vast, open region allowed megafauna and early humans to live off the land, Brigham-Grette said. However, it's still a mystery exactly when humans began crossing the land bridge.
Genetic studies show that the first humans to cross became genetically isolated from people in East Asia between about 25, to 20, years ago. And archaeological evidence shows that people reached the Yukon at least 14, years ago, Bond said. On the flip side of the equation, there are also groups of beetles that are completely unsuited to steppe-tundra, but flourish in the low shrub tundra habitats we see today in north western Alaska.
Thus, by identifying which groups of beetles are found in a fossil assemblage, it is relatively easy to identify which ecosystem existed at the time and place the beetles were living. As we all know, Alaska is an enormous state, and much of it cannot easily be reached except by float plane or helicopter very expensive means of transportation.
So unlike some other parts of the world, where fossil study sites dot the landscape like a veritable pin cushion, the number of fossil study sites in place like western and northern Alaska are few and far between.
Nevertheless, some patterns are emerging that are shedding light on the steppe-tundra question. One of the most fascinating sources of fossil materials has been cores of sediment that were drilled from the sea bed in the Bering and Chukchi Seas.
Back in the s and s, the U. Geological Survey commissioned a study of the geology of the Chukchi and Bering Sea beds, mostly as an aid to the development of oil and gas supplies. The USGS punched holes into the sea floor in many localities, taking cores that went down into the Cretaceous in some cases where the oil and gas deposits are to be found. But at the very tops of those cores, a meter or more of soft sediments were sampled.
Those sediments accumulated on the surface of the Bering Land Bridge, during the last ice age. Colleagues and I were able to sample organic-rich sediments that contained plant detritus, pollen, and insects that had lived and died on the land bridge.
The peaty sediments we studied most likely accumulated in shallow ponds or bogs on the land bridge. Our results, combined with those of other scientists, are starting to reveal an interesting pattern Elias et al.
Most of the ancient ecosystems we studied from the land bridge were quite similar to what is found in north western Alaska today. This is called mesic tundra: low tundra vegetation that requires a medium amount of moisture to grow.
It is dominated by dwarf shrubs of birch and willow, mixed with tundra herbs. There is very little grass in it — not enough to feed a hungry mammoth, for instance. This zone of mesic tundra covered much of the central and northern parts of the land bridge, and it extended east onto parts of upland Alaska, but not in a uniform pattern. Parts of south western Alaska around the Bristol Bay region were dominated by mesic tundra, as well as much of north western Alaska. But parts of the Seward Peninsula clearly had a cover of steppe-tundra.
Furthermore, some of the modern-day islands in the Bering Sea, including St Lawrence Island, had steppe-tundra vegetation. These islands would have been highlands overlooking the broad plains of the ancient land bridge.
So the pattern that is emerging is that much of the center of Beringia — the land bridge — was wetter than the surrounding uplands on either side.
Paleontologist Dale Guthrie has called this the buckle in the steppe-tundra belt.
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