Gondwanaland
Although this is written as a generalized history encompassing a
large scope of geological events and avoiding extensive use of
specialized vocabulary, it is still helpful to be familiar with
the following key concepts, or frames of reference:
Geologic Time Scale:
For convenience, the Earth history is divided into four eras. The
eras are subdivided into periods, which are further subdivided
into epochs. This chart will be useful to the reader: (from
Bradford B. Van Diver Roadside Geology of New York; Mountain
Press Publishing Company, fifth printing, 1992)
Plate Tectonics:
A theory that became one of the major building blocks of geological
sciences in this century, plate tectonics states that crust and
rigid upper mantle of the Earth behave as a unit called lithosphere.
Lithosphere is divided into approximately 12 major plates, which
ride on asthenosphere, a zone of greater plasticity. Tectonic
plates can spread apart, ride past each other, or collide,
producing ocean floors, causing seismic activity, and building
mountain chains. Thus, there are times of continental togetherness,
followed by times of continental drifting apart. These diagrams
show the position of continents at different times in Earth
history relative to each other.
A. About 200 Million Years Ago
B. About 100 Million Years Ago
C. Now
(from Bradford B. Van Diver, Roadside Geology of New York; Mountain Press Publishing Company, fifth edition,
1992)
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