Practice 2. Structure and composition of geospheres
Geosphere conception
The geosphere is considered that portion of the Earth system that includes the
Earth's interior, rocks and minerals, landforms and the processes that shape the
Earth's surface. The Earth itself is not a perfect sphere. It is what is called an oblate
spheroid, with a radius of 6,357 kilometers (km) from the Earth's center to the
North Pole and 6,378 km from the center to the Equator. Prior to advanced
instruments and spacecraft, 17th-century scientist Sir Isaac Newton predicted a
similar shape based on the effects of the Earth's daily rotation and his studies of
other planets.
The Earth's interior includes a thin, 5- to 70 km-thick layer of oceanic and
continental crust overlying an additional 6,300 km of rock and metals (Fig. 1). The
crust varies in thickness and density, with oceanic crust consisting of a thin
(around 5 km) layer of dense rock and continental crust consisting of less-dense,
lighter-colored rock ranging between 30 and 70 km in thickness. Although the
crust is comprised of many types of rocks and hundreds of minerals, these
materials are assembled from a very small number of elements. A total of 98.7% of
the crust (by weight) consists of just 8 elements, including oxygen (46.6%), silicon
(27.72%), aluminum (8.13%), iron (5.00%), calcium (3.63%), sodium (2.83%),
potassium (2.70%) and magnesium (2.09%). These elements form the building
blocks of most of the inorganic materials we encounter in our daily lives such as
glass (SiO2), concrete (CaCO3), and steel. Oceanic crust is dominated by minerals
consisting of silicon, oxygen and magnesium and is thus called SIMA; continental
crust is made up of SIAL, in which silicon and aluminum dominate.
The Earth's interior is arranged somewhat like a layer cake, consisting of a
series of layers that change in density, mineral composition and thickness with
depth. Directly below the crust is the mantle. It consists of two parts, an upper
layer that is less dense and relatively brittle and a lower (much thicker) layer that is
more dense and plastic (it deforms without breaking). The crust and upper mantle
combined form the brittle upper layers of the Earth's interior called the lithosphere.
The upper mantle is also called the asthenosphere.
Fig. 1. The structure of the lithosphere and earth interiors
The mantle makes up the largest volume of the Earth's interior. The region
beneath the mantle is called the core, and consists of two parts, a liquid outer core
that is around 2250 km thick and a solid inner core 1220 km thick. The core is
primarily made up of iron, with a small amount of nickel. The liquid iron in the
outer core is particularly important in that it is the primary source of the Earth's
magnetic field. Unlike a common magnet, though, the north and south ends of our
"global magnet" are not exactly situated at Earth's poles. Instead, the magnetic
north pole is actually situated in northern Canada, and the magnetic south pole
resides north of Antarctica and south of Australia. Another interesting feature of
the magnetic poles is that their precise location moves over time. Every few
million years, even the polarity of the Earth's magnetic field reverses (called a
geomagnetic reversal, where magnetic north and south "switch"). While scientists
still do not fully understand why geomagnetic reversals occur, the presence of
changing magnetic orientations preserved in rocks containing iron was a
fundamental clue in unravelling the puzzle of Plate Tectonics. Almost all of our
direct knowledge of the Earth's interior is from the upper 10 km. Our knowledge of
the remaining 6,300 km is based largely on indirect evidence from seismology,
laboratory studies of igneous and metamorphic rocks, computer models and
meteorites.
(Источник: http://earth.rice.edu/mtpe/geo/geosphere.html)
Task 1:
1. Use supplement materials that to learn the information on geospheres.
2. Give the definitions to terms: atmosphere, lithosphere, hydrosphere,
biosphere.
3. Give a schematic illustration of the Earth structure and geospheres, specify
structural elements and chemical composition.
Task 2:
Describe the following scheme based on knowledge, obtained in lectures and
supplement materials.
Fig. 2. General outline of exogenic and endogenic cycles (source: Manahan S.E.,
2000)
Recommended information sources:
Glazovsky N. Environmental structure and function: Earth system.
Encyclopedia of Life Support Systems (EOLSS). – 2014. URL:
https://www.eolss.net
Manahan, Stanley E. ENVIRONMENTAL SCIENCE, TECHNOLOGY,
AND CHEMISTRY. In: Environmental Chemistry. – Boca Raton: CRC Press
LLC, 2000.