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tectonics plate
Plate Boundaries
dynamic earth
EARTH!
a theory of global tectonics in
which
the lithosphere is divided into a number of crustal plates, each of which moves on the plastic asthenosphere more or less independently to collide with, slide under, or move past adjacent plates.
A theory stating that the Earth's
continents
have been joined together and have moved away from each other at different times in the Earth's history
A former “supercontinent” on the
Earth
. In the distant past a large landmass, Pangaea, included all the present
continents
, which broke up and drifted apart.
The upper part of the Earth's mantle, extending from a depth of about 75 km (46.5 mi) to about 200 km (124 mi). The asthenosphere lies beneath the lithosphere and consists of partially molten rock.
seismic waves
passing through this layer are significantly slowed. Isostatic adjustments (the depression or uplift of
continents
by buoyancy) take place in the asthenosphere, and magma is believed to be generated there. Compare
atmosphere
, hydrosphere, lithosphere.
In the Earth, the lithosphere includes the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The lithosphere is underlain by the
asthenosphere
, the weaker, hotter, and deeper part of the upper mantle. The boundary between the lithosphere and the underlying asthenosphere is defined by a difference in response to stress: the lithosphere remains rigid for very long periods of geologic time in which it deforms elastically and through brittle failure, while the asthenosphere deforms viscously and accommodates strain through plastic deformation. The lithosphere is broken into
tectonic plates
. The uppermost part of the lithosphere that chemically reacts to the
atmosphere
,
hydrosphere
and
biosphere
through the
soil forming process
is called the
pedosphere
.
A series of mountain ranges on the ocean floor, more than 84,000 kilometers (52,000 miles) in length, extending through the North and South Atlantic, the Indian Ocean, and the South Pacific. According to the plate tectonics theory, volcanic rock is added to the sea floor as the mid-ocean ridge spreads apart
The largest freshwater lakes in the world are all located in rift valleys except for Lake Victoria.
[2]
Lake Baikal
in
Siberia
, a
World Heritage Site
,
[3]
lies in an active rift valley. Baikal is both the deepest lake in the world and, with 20% of all of the liquid freshwater on earth, has the greatest volume.
[4]
Lake Tanganyika
, second by both measures, is in the
Albertine Rift
, the westernmost arm of the active
East African Rift
.
Lake Superior
in
North America
, the largest
freshwater
lake
by area, lies in the ancient and dormant
Midcontinent Rift
. The largest subglacial lake,
Lake Vostok
, may also lie in an ancient rift valley.
[5]
Lake Nipissing
and
Lake Timiskaming
in
Ontario
and
Quebec
,
Canada
lie inside a rift valley called the
Ottawa-Bonnechere Graben
.
[6]
Þingvallavatn
,
Iceland's
largest natural lake, is also an example of a rift lake.
A geologic process in which one edge of one crustal plate is forced below the edge of another.
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