Download Discovery Education: Earth`s Spheres interactive text

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Discovery Education: Earth’s Spheres interactive text
What are the major components of the spheres of the Earth system?
Many Spheres
Earth can be divided into various spheres that describe the planet’s land, water, gas air, and life.
The geosphere describes the solid exterior and interior of the planet. The hydrosphere consists of
all the water on the planet’s surface, including the oceans, lakes, ice, rivers and the moisture in
the air. The atmosphere consists of the “ocean” of air that surrounds the surface of the planet. A
fourth sphere, the biosphere, consists of all life on Earth. So, the biosphere includes aspects of
Earth’s other spheres.
Earth’s spheres continuously interact. One such example involves the element carbon, which
cycles through all of Earth’s spheres.
The Geosphere
The geosphere consists of Earth’s core, mantle, and crust. The core is divided into two sections.
The solid inner core has a radius of 1,200 km. The liquid outer core, which is 2,250 km thick,
surrounds the inner core. At 2,900 km, the mantle is the thickest region of the planet. The mantle
is divided into three sections. The mesosphere, the asthenosphere, and the rigid, upper section of
the mantle next to the crust. This portion of the mantle and the crust is referred to as
the lithosphere.
The crust is the solid exterior of the planet. It is composed of rocks and minerals. Eight elements
dominate the rocks and minerals. These eight elements are 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%).
Earth’s crust is classified as oceanic or continental. Oceanic crust is composed primarily of iron
and magnesium silicate minerals. It is 4- to 6-km thick and very dense. Continental crust is
composed primarily of aluminum silicate minerals. It is 30- to 70-km thick. Oceanic crust is
denser than continental crust. It sinks beneath continental crust at locations where they come
together.
The crust and the uppermost part of the mantle form the lithosphere. The lithosphere moves
across the planet’s surface in large sections called plates.
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The Hydrosphere
Seventy percent of the planet’s surface is covered with water. The hydrosphere includes all water
in the Earth system. Ninety-seven percent of water on Earth is found in the oceans. The
remaining liquid water is found in lakes, rivers, and groundwater. Water is also found as ice and
in the atmosphere.
Water is classified by its percentage of dissolved solids. Fresh water is characterized by low
concentration of dissolved solids. Fresh water is typically less than 0.5 parts per thousand.
Saltwater is classified by higher concentrations of dissolved solids. Brackish water contains 0.5–
30 parts-per-thousand (ppt) dissolved solids. Saline water, commonly called saltwater, contains
30–50 parts-per-thousand dissolved solids. Brine contains more than 50 parts-per-thousand
dissolved solids. The ocean has an average salinity of 35 ppt.
The Hydrologic/Water Cycle: The hydrologic cycle describes how water transitions from
one reservoir to another.
The Cryosphere
The Cryosphere is the part of the Hydrosphere that contains
water in its solid form. Frozen water comes in a variety of
forms. Snow, which is frozen precipitation, is found
throughout the world. Ice is also found throughout the world
in the form of glaciers, ice shelves, sea ice, icebergs, and
permafrost. These features vary in scale. Glaciers are massive
sheets of ice on land. An ice shelf is a glacier that moves off
land into a body of water. Sea ice forms from frozen ocean water. Permafrost is
permanently frozen land.
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The Atmosphere
The atmosphere consists of a gaseous mixture of air that surrounds
the surface of the planet. Volcanoes released many of the gases that
make up the atmosphere. Nitrogen dominates the mixture because it
does not react with minerals and rocks at Earth’s surface. The
concentration of nitrogen has increased slowly through time. It now
makes up 78 percent of all gases in the atmosphere. The next most
abundant gas in the atmosphere is oxygen, which has stabilized at 21
percent. The oxygen in the atmosphere is a product of photosynthetic organisms.
The remaining gases are found in the atmosphere in trace amounts. Several of the trace gases
have a tremendous impact on the planet. Carbon dioxide, water vapor, methane, sulfur dioxide,
ozone, and nitrogen oxides are greenhouse gases. These gases absorb long-wavelength radiation
from Earth’s surface that is heated by the Sun. The higher the concentration of greenhouse gases
in the atmosphere, the more heat is kept close to the planet’s surface.
If the atmosphere did not absorb this long-wavelength radiation, the planet would still heat up
during the day. However, the heat would be lost to the upper atmosphere at night. The rapid
transition in temperature during this 24-hour cycle would affect the ability of life to survive on
the planet’s surface.
The Biosphere
The biosphere consists of those parts of the planet
where life can exist. It forms a narrow layer ranging
from approximately 11 km beneath the ocean’s
surface to 9 km in the air. It extends from the
equator to the polar ice caps. Thus, the biosphere
consists of parts of the geosphere, hydrosphere, and
atmosphere.
Why does life exist where it does on Earth? The
most important factors are the existence of liquid
water and the flow of energy. Earth’s atmosphere allows enough solar radiation to reach the
planet’s surface to maintain an average global temperature of approximately 15°C. Much less
solar radiation and the planet would become too cold for life (like Mars); much more solar
radiation and the planet would become too hot (like Venus).
In terms of energy, Earth is an open system—the planet is continually gaining and losing energy.
In terms of matter, however, Earth is considered a closed system. While organisms live, they
absorb nutrients from their environments; when they die and decompose, the matter that makes
up their bodies returns to the environment. In this way, the biosphere is continually replenished
to make way for new life. A huge diversity of organisms, linked by food webs and other
relationships, are involved in this process. The maintenance of a healthy biosphere therefore
requires the careful stewardship of high levels of biological diversity.
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Earth’s Magnetic Field
Earth is subjected to material ejected from the Sun’s surface. This material moves like wind
through space. The interaction between charged particles in the solar wind and Earth’s magnetic
field produces a region of space around the planet that deflects most of the charged particles
ejected from the Sun. This region is called the magnetosphere. The bow shock describes the
frontal blast of the ions as they approach Earth. The charged particles are heated, which slows
them as they deflect around Earth. As the ions pass the planet, this region expands to 1,000 times
Earth’s radius, producing the magnetotail.