| Evidence of past glaciation in locations
such as southern Africa, Australia, and India, long confounded scientists. Plate tectonic
theory solved this problem. As the Earth's tectonic plates migrate at a rate of 1-16 cm
per year, the continents move in and out of polar areas. In the adjacent image we see the
continents clustered in the southern hemisphere. This continent cluster, known as Pangaea,
created a large land mass at high southern latitudes, allowing for a great glacial extent
about 300 million years ago. Note that such current glaciated areas as Alaska, and
Scandinavia were then located near the Equator and devoid of any glaciation. Today we
would not find glaciers in southern Africa, India, or Australia. Plate motion can also redirect ocean currents, as by the closing of the
Isthmus of Panama about 5 million years ago. that barrier deflected the Gulf Stream
to the NE, helping initiate glaciation of iceland, Geenland, and the rest of the Northern
Hemisphere.
(To view a 1 Mb animation from
Cal-Berkeley of plate movement, assembing and destroying Pangea, please click here. To view
reconstructions by Chris Scotese of former continental positions across time, especially
glacial periods such as the Last ice Age, Late Carboniferous, and late Precambrian, click here.) |
[Image of Pangaea not yet acquired] |
