Download Structure of the Earth Lithosphere System In this lecture we will learn

Structure of the Earth
Lithosphere System
In this lecture we will learn about the structure and what the Earth is composed of and how it affects
landscape development.
The Earth is an oblate spheroid. It is composed of a number of different layers as determined by
deep drilling and seismic evidence, collected through a Seismograph. These layers are:
1. The core which is located at the Earth's center, (a) inner core and (b) outer core
2. The mantle which surrounds the core and has a thickness of 2900 kilometers. It covers
83% of the Earth's volume
3. The crust floats on top of the mantle. It is composed of basalt rich oceanic crust and
granitic rich continental crust.
Figure -1: Layers beneath the Earth's surface.
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The core forms 1/3 of Earth’s mass, with a radius of 2100 miles/3360 Km,
It is believed to be composed of iron and nickel, and is composed of two layers:
the inner and outer cores.
The inner core is theorized to be solid Iron and a radius of about 1220 kilometers.
The outer core is liquid and surrounds the inner core and has an average thickness of
about 2250 kilometers.
The mantle is almost 2900 kilometers/1800mi thick and comprises about 83% of the
Earth's volume. It is composed of several different layers.
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The top layer of the upper mantle, 100 to 200 kilometers below surface, is called the
asthenosphere, has characteristics of plastic solid and can deform and flow
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The lithosphere layer that includes the crust and the upper most portion of the
asthenosphere (Figure 2).
The topmost part of the lithosphere consists of crust. This material is cool, rigid, and
brittle.
Two types of crust can be identified: oceanic crust and continental crust (Figure 3).
Ocean crust is thin and measures between 5 to 10 kilometers thick. It is also composed
of basalt
The continental crust is 20 to 70 kilometers thick and composed mainly of lighter
granite. Continental crust is thickest beneath mountain ranges and extends into the
mantle.
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The lithosphere consists of the oceanic crust, continental crust, and uppermost mantle. Beneath the lithosphere is
the asthenosphere. This layer, which is also part of the upper mantle, extends to a depth of about 200 kilometers.
Sedimentary deposits are commonly found at the boundaries between the continental and oceanic crust.
Both of these crust types are composed of numerous tectonic plates that float on top of the
mantle. Convection currents within the mantle cause these plates to move slowly across the
asthenosphere.
Plate Tectonics
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In the 19th and early 20th centuries, several scientists suggested that the continental
masses had the ability to move across the Earth's surface.
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According to this theory, the Earth's crust is composed of several continental plates that have
the ability to move.
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First proposed by A. Snider in 1858 and developed by F.B. Taylor (1908) and Alfred Wegener
(1915). These early theories of continental drift were based on the following evidence:
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Some continents seem to fit together like a jigsaw puzzle. Supercontinent/Pangaea
Some geologic deposits of rocks on the East coast of North and South America are
similar to deposits found on the West coast of Africa and Europe.
During the first 30 years of this century the theory of continental drift was actively debated
among geo-scientists.
In the 1960s, the theory was resurrected with the discovery of alternating patterns of rock
magnetism in surface sea-floor rocks.
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