Definition (Encyclopedia of Global Resources)
Overview (Encyclopedia of Global Resources)
The interior of the Earth has a number of layers, or concentric spheres. At the center of the Earth is the inner core. Then, moving outward, come the outer core, the lower mantle, the upper mantle, and the Earth’s crust. Scientists subdivide the upper mantle into the asthenosphere, a partially molten zone, and, above that, the lithosphere. The lithosphere, then, is the rigid (or brittle) outer shell of the Earth, which extends to a depth of between 70 and 100 kilometers and rests on the asthenoshere. It includes the Earth’s crust and part of the upper mantle.
The upper mantle is approximately 700 kilometers thick. The asthenosphere begins at a depth of approximately 70 to 100 kilometers and shows a rapid increase in density and a temperature in excess of 1,000° Celsius. The asthenosphere is partially molten ultramafic material. Because of its partially molten properties, the asthenosphere probably exhibits plastic flow. Above the asthenoshere, the upper brittle portion of the upper mantle that is part of the lithosphere is a dense ultramafic material that directly underlies the Earth’s crust. The lithosphere comprises seven to ten major lithospheric “plates” that move slowly as they rest on the asthenosphere. plate tectonics refers to the movement of these plates and the land and ocean forms that are created as a result.
Within the lithosphere, the boundary between the upper mantle and the crust is called the...
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Definition (Encyclopedia of Global Warming)
Besides compositional classification, the Earth is separated into layers based on mechanical properties. The topmost layer is called the lithosphere, composed of tectonic plates that float on top of another layer known as the asthenosphere. The term lithosphere is derived from the Greek words lithos, meaning rock, and sfaira, or sphere. The rigid, brittle lithosphere extends about 70 kilometers and is made up of Earth’s crust and the upper part of the mantle underneath. It is broken into a mosaic of rigid plates that move parallel across the Earth’s surface relative to each other.
The lithosphere rests on a relatively ductile, partially molten layer known as the asthenosphere, which derives its name from the Greek word asthenes, meaning “without strength.” The asthenosphere extends to a depth of about 400 kilometers in the mantle, over which the lithospheric plates slide along. Slow convection currents within the mantle, generated by radioactive decay of minerals, are the fundamental heat energy source that causes the lateral movements of the plates on top of the asthenosphere. According to the plate tectonic theory, there are approximately twenty lithospheric plates, each composed of a layer of continental crust or oceanic crust. These plates are separated by three types of plate boundaries. At divergent boundaries, tensional forces dominate the interaction between the lithospheric plates, and...
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Significance for Climate Change (Encyclopedia of Global Warming)
Volcanic eruptions have severe effects on global climate. The greenhouse effect, icehouse effect, and ozone depletion by far have gained the most attention in climate research and planning. In addition to lava and pyroclastic materials (fragments of hot and molten rocks), volcanoes emit a variety of gases such as water vapor, carbon dioxide (CO2), carbon monoxide (CO), chlorine, fluorine, and sulfur dioxide (SO2). Both CO2 and CO are greenhouse gases (GHGs) that contribute to global warming by creating a shield over the Earth that prevents heat from escaping into the atmosphere.
In contrast, SO2 gas causes short-term cooling resulting from what is known as the icehouse effect. In the lower atmosphere, SO2 gas is converted to sulfuric acid (H2SO4), which condenses to form a thick layer of sulfate aerosol. The suspended aerosols increase Earth’s albedo by reflecting the Sun’s rays back to space and cause cooling of the Earth’s surface. An anomalous increase in SO2 layers in the atmosphere and decrease in average temperature correlates significantly with several volcanic eruptions. The 1991 eruptions of Mount Pinatubo in the Philippines were responsible for about a 0.5° Celsius decrease in global temperature and an unusually cold summer in 1992 in the intermediate latitude of the Northern Hemisphere.
Although volcanic activity increases the global temperature by adding CO2 to the atmosphere, a much...
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Further Reading (Encyclopedia of Global Warming)
Gerlach, Terrence M., et al. “Carbon Dioxide Emission Rate of Kilauea Volcano: Implications for Primary Magma and the Summit Reservoir.” Journal of Geophysical Research 107 (2002). Comparative study of anthropogenic and volcanic CO2 emissions.
Schuiling, Roelof D. “Thermal Effects of Massive CO2 Emissions Associated with Subduction Volcanism.” Comptes Rendus Geosciences 336 (2004). Study of CO2 emitted during volcanic activity that is not concentrated in volcanic centers. Such CO2 derives from the decarbonization of subducted limestones and carbonated metabasalts.
Zielinski, Gregory A. “Use of Paleo-Records in Determining Variability Within the Volcanism-Climate System.” Quaternary Science Reviews 19 (2000). Focuses on the volcanic eruptions that inject SO2 into the stratosphere, resulting in global climate cooling. Examines variations in cooling by latitude.
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Lithosphere (World of Earth Science)
The word lithosphere is derived from the word sphere, combined with the Greek word lithos, meaning rock. The lithosphere is the solid outer section of Earth, which includes Earth's crust (the "skin" of rock on the outer layer of planet Earth), as well as the underlying cool, dense, and rigid upper part of the upper mantle. The lithosphere extends from the surface of Earth to a depth of about 442 mi (7000 km). This relatively cool and rigid section of Earth is believed to "float" on top of the warmer, non-rigid, and partially melted material directly below.
Earth is made up of several layers. The outermost layer is called Earth's crust. The thickness of the crust varies. Under the oceans, the crust is only about 3 mi (50 km) thick. Under the continents, however, the crust thickens to about 22 mi (35 km) and reaches depths of up to 37 mi (60 km) under some mountain ranges. Beneath the crust is a layer of rock material that is also solid, rigid, and relatively cool, but is assumed to be made up of denser material. This layer is called the upper part of the upper mantle, and varies in depth from about 312 mi (5000 km) below Earth's surface. The combination of the crust and this upper part of the upper mantle, which are both comprised of relatively cool and rigid rock material, is called the lithosphere.
Below the lithosphere, the temperature is believed to reach 1,832°F (1,000°C), which is warm enough to allow rock material to flow if pressurized. Seismic evidence suggests that there is also some molten material at this depth (perhaps about 10%). This zone which lies directly below the lithosphere is called the asthenosphere, from the Greek word asthenes, meaning weak. The lithosphere, including both the solid portion of the upper mantle and Earth's crust, is carried "piggyback" on top of the weaker, less rigid asthenosphere, which seems to be in continual motion. This motion creates stress in the rigid rock layers above it, forcing the slabs or plates of the lithosphere to jostle against each other, much like ice cubes floating in a bowl of swirling water. This motion of the lithospheric plates is known as plate tectonics, and is responsible for many of the movements seen on Earth's surface today including earthquakes, certain types of volcanic activity, and continental drift.
See also Continental drift theory; Earth (planet); Earth, interior structure