The current theory among archaeologists is that humans first entered North America from Asia across the Bering Land Bridge less than 12, 000 years ago when continental ice sheets were receding.
42.
These glaciers were the massive continental ice sheets that began to cover large parts of Ohio and other states downstream ( west ) of Ohio between 2.5 and 3 million years ago.
43.
The archipelago is unique in that it features ridged washboard moraines known as De Geer moraines, formed by the melting of the continental ice sheet 10, 000 to 24, 000 years ago.
44.
It broke up between about 11, 000 and 9, 000 years ago, and the present northern Channel Islands took their shape after the continental ice sheets melted and sea levels rose by about 100 meters.
45.
It's considered a volcanic vent of Mount Price, and has produced two large lava flows approximately 9, 000 years ago, that ponded against the retreating continental ice sheet and formed The Barrier, containing Garibaldi Lake.
46.
An "'ice age "'is a period of long-term downturn in the temperature of Earth's climate, resulting in an expansion of the continental ice sheets, polar ice sheets and mountain glaciers ( " glaciation " ).
47.
Evidence suggests the seals are descended from Arctic ringed seals that reached the area from the north during an earlier part of the Quaternary period and became isolated in the landlocked Caspian Sea when continental ice sheets melted.
48.
The Saint Croix in Minnesota and Wisconsin is another important river in the Driftless Area, as it was the outlet for Glacial Lake Duluth, forerunner to Lake Superior, when the eastern outlet was blocked by the continental ice sheet.
49.
It and these other periods of rapid sea level rise are known as " meltwater pulses " because the inferred cause of them was the rapid release of meltwater into the oceans from the collapse of continental ice sheets.
50.
Human activities promoting climate change, notably the extensive use of fossil fuels over the last 150 years and the resulting increase in atmospheric CO 2 concentrations, are the principal cause of the more rapid retreat of alpine glaciers and continental ice sheets all across the world.
