 |
|
|
|
Proterozoic
Mountains and Glaciers
In
the Proterozoic Eon, four major mountain-building episodes occurred,
each of which was followed by an interval of continental erosion.
Mountain-building was caused by converging plates, just as occurs
in present-day plate tectonics. It was accompanied by intrusions of
molten granite that welded an additional belt of younger, igneous
rock around the edges of the original microcontinents. In North America,
the Proterozoic episodes of mountain-building greatly expanded the
size of the continent.
Widespread continental glaciations evidently occurred
at least twice in the Proterozoic, once near its beginning and again
near its end. Several of these glaciations extended almost to the
equator, much farther south than any recent cooling events. This unusual
situation has led a few geologists to propose that the Earth was almost
entirely covered by glaciers for perhaps several million years during
the Proterozoic. During this “Snowball Earth” phase, life
would have been relegated to hydrothermal vents and other such refuges
until the build-up of carbon dioxide released from volcanoes warmed
Earth from its deep-freeze. The final Marinoan Ice Age marked the
transition to the Cambrian, the first period of the
Paleozoic Era. |
Eon Overview |
Earth's Crust as a Platform for Prokaryotic Life |
Eukaryotes and the First Multicellular Life Forms |
Changes in the Atmosphere |
Proterozoic Mountains and Glaciers
Department of Paleobiology Home |
National Museum of Natural History Home
Smithsonian Institution Home
|
|
