Transcript ENVIRONMENTAL SCIENCE

ENVIRONMENTAL SCIENCE
Chapter 3 The Dynamic Earth
3.1 The Geosphere
3.1 The Geosphere Objectives
• Describe the composition and structure of the
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Earth.
Describe the Earth’s tectonic plates.
Explain the main cause of earthquakes and their
effects.
Identify the relationship between volcanic
eruptions and climate change.
Describe how wind and water alter the Earth’s
surface.
The Earth as a System
• The Earth is an integrated system made of four
major systems that constantly interact and affect
one another.
– Geosphere – solid part of Earth, the rocks, soil, and
sediment
– Atmosphere – envelope of gases that surround the
Earth
– Hydrosphere – all of the water on Earth
– Biosphere – all of the living things (organisms) on
Earth
The Earth as a System
• The majority of the geosphere is located beneath the
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surface of the Earth.
The average diameter of the Earth at the equator is
12,756 km.
Most of the molecules that make up the atmosphere are
found in the lower 30 km of our atmosphere.
Oceans cover about 71% of the Earth’s surface.
The life, or biosphere can be found living from the
bottom of the ocean to about 9 km above sea level – a
total range of about 20 km.
Discovering Earth’s Interior
• The Earth’s interior cannot be studied through
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direct observation – the deepest well drilled is
only about 12 km deep.
Scientists use seismic waves to study the
structure of the Earth’s interior.
A seismic wave is altered by the material
through which it travels.
Seismologists measure the speed and direction
of seismic waves as they penetrate the Earth’s
interior.
Discovering Earth’s Interior
• The Earth can be divided into three
compositional layers.
– Crust
– Mantle
– Core
• These layers are made with progressively
denser material closer to the Earth’s
center.
Discovering Earth’s Interior
• The crust is a thin, outer layer of the Earth
made almost entirely of lighter elements.
• The crust makes up less than 1% of
Earth’s mass.
• Oceanic crust is 5 km to 8 km thick and
made mostly of basalt.
• Continental crust, mostly granite based, is
between 20 km to 70 km thick.
Discovering Earth’s Interior
• The mantle, just below the crust, makes
up 64% of the mass of the Earth.
• The mantle is about 2,900 km thick and is
made mostly of medium density rock.
• The core, Earth’s inner-most layer, is
composed of the densest elements and
has a radius of about 3,400 km.
Discovering Earth’s Interior
• The Earth, based on physical properties, can be divided
into five layers.
– Lithosphere (15 to 300 km thick) a cool, rigid layer that includes
the crust and the upper part of the mantle and is divided into
large tectonic plates
– The asthenosphere (250 km thick) is a plastic, solid layer of the
mantle that flows very slowly and allows tectonic plates to move
on top of it
– Mesosphere – (2,550 km thick) the lower layer of the mantle
between the asthenosphere and the outer core
– Outer core (2,200 km thick) outer shell of Earth’s core made of
liquid nickel and iron
– Inner core – (1,228 km radius) sphere of solid nickel and iron at
the Earth’s center
Plate Tectonics
• The Earth’s lithosphere is divided into large tectonic
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plates which glide across the underlying asthenosphere
much like chunks of ice setting on a frozen lake.
The continents are located on tectonic plates and move
around with them over time.
Much of the geologic activity that occurs at the Earth’s
surface takes place at tectonic plate boundaries.
The formation of mountains and volcanoes, as well as
violent earthquakes, are the result of the forces of
tectonic activity.
Plate Tectonics
• There are three
types of plate
boundaries.
– Convergent
• Ocean – ocean
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collision
Ocean – continent
collision
Continent –
continent collision
– Divergent
– Transform
Earthquakes
• A fault is a fracture in the bedrock along which
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movement has occurred.
When rocks are under stress along a fracture,
they can sometimes snap as the stress is
released.
The vibrations which travel through the ground
as a result of this release of energy are known
as earthquakes.
Earthquakes occur all the time, but most are not
felt (only detected by instrumentation).
Earthquakes
• The amount of energy released by an
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earthquake can be quantified and compared on
the Richter Scale.
The smallest magnitude that can be felt is 2.0
and the largest magnitude ever recorded was
9.5.
An increase in magnitude of whole number
indicates the release of 31.7 times more energy
than the number below it.
The majority of earthquakes occur along plate
margins.
Earthquakes
• Though earthquakes
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cannot be accurately
predicted, risk for
earthquakes can be
better assessed.
Earthquakes can
damage roads, gas
lines, electrical
supply, sewage, and
even large buildings.
Volcanoes
• Volcanoes are mountains build from molten rock
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(magma and lava) and are often located near
tectonic plate boundaries.
Most of the world’s active volcanoes on land are
located on tectonic plate boundaries that
surround the Pacific Ocean.
Volcanic eruptions can be devastating locally
with gas and pyroclastic flows that can exceed
200 km/hr.
Ash from eruptions can also be carried in the
atmosphere and travel far.
Volcanoes
• Volcanic eruptions can
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alter global weather
conditions.
When Mt. St. Helens
erupted in 1980,
average global
temperature dropped
slightly.
Erosion
• The Earth’s surface is subject to the effects of
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weathering and erosion.
Wind and water are constantly working to
remove and transport surface materials.
Water erosion, over time, can dramatically
change the landscape.
– For example, the Grand Canyon was created by
stream erosion over time
• Wind erosion is most evident in desert and
beach areas.
References
• Earth’s Compositional Layers - http://www•
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cms.llnl.gov/s-t/extreme_chemistry.html
Earth’s Structural Layers http://schoolscience.rice.edu/science/curricula/p
rintpreview-noimage.cfm?CurriculaID=315
Earth Structure Compared http://elmo.shore.ctc.edu/ebaer/Geology%2010
1/tests/test1key.html
Tectonic Plates http://www.stchas.edu/faculty/ewilson/Photos/Pl
ates
References
• Earthquake Distribution •
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http://www.geology.uiuc.edu/~hsui/classes/geo116/lect
ures/earthquakes-demo.htm
Earthquake in San Francisco http://www.geology.uiuc.edu/~hsui/classes/geo116/lect
ures/earthquakes-demo.htm
Tectonic Plate Boundaries http://www.scarborough.k12.me.us/wis/teachers/dtewhe
y/webquest/nature/plate%20boundaries.htm
Pyroclastic Flow http://www.geo.umn.edu/courses/1001/Summer_Sessio
n/SedImages.html
References
• Mt. St. Helens -
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http://geosciences.ou.edu/~msoreg/volcanoes/
Mt_StHelens1.html
Death Valley Sand Dunes http://www.beachdoctor.com/sethmedlin/Family
%20Travel%20Death%20Valley%20April%2020
03.htm
Grand Canyon - http://www.evcforum.net/cgibin/dm.cgi?action=msg&f=7&t=162&m=1