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The Important Thing
About Geoscience
By Jody Decker- Bader
The important thing about geoscience is that
there are processes that continually change
the surface of the Earth.
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The structure of the Earth is in
layers.
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The top layer is called the
crust.
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Below the crust is the mantle.
The mantle is made up of a
different kind of rock than the
crust.
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The upper rigid part of the
mantle, together with the
crust, is called the
lithosphere. It is broken into
sections called plates, much
the same way as the shell of a
hard boiled egg can be cracked
into sections.
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On the crust there are
oceanic plates and
continental plates.
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Below the lithosphere is the
part of the upper mantle called
the asthenosphere. The
asthenosphere contains
magma.
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The lithosphereic plates float
and move on top of the
moveable asthenosphere.
This is the process that continually changes the
surface of the Earth.
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Movement happens along plate
boundaries.
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Geologists classify these
movements into three
categories.
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The first is a divergent
boundary, where two plates
move away from each other.
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On the ocean floor a midocean ridge is created when
magma from the
asthenosphere rises upward.
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The magma fills in the gap
where the sea floor spread.
Divergent Boundary
Mid-ocean ridge
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When the asthenosphere rises
beneath a continent, the
lithosphere bulges upward and
is stretched sideways forming
long cracks that eventually fall
into themselves creating a rift
valley.
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The East African Rift Valley is
an example of a divergent
boundary on a continental
plate.
This is a process that continually changes the
surface of the Earth.
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The second is a convergent
boundary, where two plates
move toward each other.
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A subduction zone is formed
when the denser heavier
oceanic plate is pushed under
a continental plate.
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Off the coast of the Pacific NW
the Juan de Fuca plate is
subducting underneath the
North American Plate.
Convergent Boundary
Subduction Zone
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Convergent boundaries can
also happen between two
continents.
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When two continents collide
and are welded together a
suture zone is formed.
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An example of a continentalcontinental convergent
boundary is the collision of
India and Asia, which began
about 45 million years ago,
producing the majestic
Himalayan mountains.
Convergent Boundary
Suture Zone
This is a process that continually changes the
surface of the Earth.
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Volcanoes are also common
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Magma is produced above the
subducted plate, and rises
toward the surface because it
is less dense than the
surrounding rock. The “Ring of
Fire” around the Pacific Ocean
is caused by this melting at
subduction zones all around
the Pacific.
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Hot spot volcanoes, like
along subduction zones, where
they form volcanic arcs.
Hawaii, are produced when
narrow plumes of unusually
hot mantle material rise up
through the lithosphere,
creating pools of magma.
This is a process that continually changes the
surface of the Earth.
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The third classification of plate
boundary movement is a
transform boundary, where
two plates slide parallel to each
other.
Transform Boundary
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The surface along which the
plates slide is called a
transform fault. The longest
and most famous transform
fault is the San Andreas Fault in
California.
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When plates move past each
other the movement is not
always smooth. Earthquakes
happen when the rocks at
plate boundaries can no longer
withstand the pressure and
move suddenly.
This is a process that continually changes the
surface of the Earth.
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Geoscientists believe that the
process of thermal
convection moves the plates.
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Geoscientists divide Earth into
five main layers: the inner
core, the outer core, the lower
mantle, the upper mantle or
asthenosphere, and the
lithosphere.
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The core is made mostly of
iron and is so hot that the
outer core is molten.
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This heat from the core is also
what keeps the mantle moving
in a slow viscous manner,
much like melted plastic.
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Heat from deep in the Earth
rises toward the surface. It
spreads out horizontally, cools,
and sinks back into the
interior.
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These extremely slow moving
flows are called convection
cells.
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Scientists hypothesize that
convection cells are what help
move the lithospheric plates.
This is the process that continually changes the
surface of the Earth.
In conclusion, Plate Tectonics Theory states that 225 million years ago
the Earth’s lithosphere was combined into one supercontinent named
Pangaea. Over million of years the lithospheric plates assemble, break
up, and reassemble.
Thermal convection cells distribute heat from deep inside the Earth. This
enables the plates to float upon and move on top of the viscous
asthenosphere.
But, the important thing about geoscience is
that there are processes that continually
change the surface of the Earth.