Download Light: The Cosmic Messenger

Erosion of Craters
• Details of some
craters suggest
they were once
filled with water.
© 2010 Pearson Education, Inc.
Martian Rocks
• Mars rovers have found rocks that appear to have
formed in water.
© 2010 Pearson Education, Inc.
Hydrogen Content
• Map of hydrogen content (blue) shows that lowlying areas contain more water ice.
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Crater Walls
• Gullies on crater
walls suggest
occasional liquid
water flows have
happened less
than a million
years ago.
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“Seeing” the Surface Geology of Venus
• Its thick atmosphere forces us to explore Venus’s
surface through radar mapping.
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Cratering on Venus
• Venus has impact
craters, but fewer
than the Moon,
Mercury, or Mars.
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Volcanoes on Venus
• It has many
volcanoes, including
both shield volcanoes
and stratovolcanoes.
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Tectonics on Venus
• The planet’s
fractured and
contorted surface
indicates tectonic
stresses.
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Erosion on Venus
• Photos of rocks
taken by landers
show little
erosion.
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Does Venus have plate tectonics?
•
Venus does not appear to have plate
tectonics, but entire surface seems to have
been “repaved” 750 million years ago.
© 2010 Pearson Education, Inc.
Earth’s Destiny
• Many of Earth’s
features are
determined by its
size, rotation, and
distance from Sun.
• The reason for plate
tectonics is not yet
clear.
© 2010 Pearson Education, Inc.
Earth’s Destiny
• Many of Earth’s
features are
determined by its
size, rotation, and
distance from Sun.
• The reason for plate
tectonics is not yet
clear.
© 2010 Pearson Education, Inc.
Earth’s Destiny
• Many of Earth’s
features are
determined by its
size, rotation, and
distance from Sun.
• The reason for plate
tectonics is not yet
clear.
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Plate Tectonics on Earth
• Earth’s continents slide around on separate
plates of crust.
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How do we know that Earth’s
surface is in motion?
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Continental Motion
• Motion of the continents can be measured with
GPS.
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Continental Motion
• The idea of
continental drift
was inspired by
the puzzle-like fit
of the continents.
• Mantle material
erupts where the
seafloor spreads.
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Seafloor Crust
• Thin seafloor
crust differs
from thick
continental crust.
• Dating of the
seafloor shows
that it is usually
quite young.
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How is Earth’s surface shaped by
plate tectonics?
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Seafloor Recycling
• Seafloor is recycled through a process known
as subduction.
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Surface Features
• Major geological features of North America
record the history of plate tectonics.
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Surface Features
• The Himalayas
formed from a
collision
between plates.
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Surface Features
• The Red Sea is
formed where
plates are pulling
apart.
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Rifts, Faults, Earthquakes
• The San Andreas
fault in
California is a
plate boundary.
• Motion of plates
can cause
earthquakes.
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Plate Motions
• Measurements of plate motions tell us past and
future layout of the continents.
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Hot Spots
• The Hawaiian islands have formed where a plate
is moving over a volcanic hot spot.
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Carbon Dioxide Cycle
1. Atmospheric CO2
dissolves in
rainwater.
2. Rain erodes minerals
that flow into ocean.
3. Minerals combine
with carbon to make
rocks on ocean floor.
© 2010 Pearson Education, Inc.
Carbon Dioxide Cycle
4. Subduction carries
carbonate rock down
into mantle.
5. Rock melts in
mantle and CO2 is
outgassed back into
atmosphere through
volcanoes.
© 2010 Pearson Education, Inc.
Radiation Absorption in the
Earth’s Atmosphere
Solar X-rays are absorbed high
in the atmosphere
Solar ultraviolet light is
absorbed by ozone in the
mid atmosphere
Visible light reaches the
ground and warms the surface
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Why the Sky Is Blue
• Atmosphere scatters
blue light from Sun,
making it appear to
come from different
directions.
• Sunsets are red because
red light scatters less.
© 2010 Pearson Education, Inc.
Dangers of Human Activity
• Human-made CFCs in the atmosphere
destroy ozone, reducing protection from
ultraviolet radiation.
• Human activity is driving many species to
extinction.
• Human use of fossil fuels produces
greenhouse gases that can cause global
warming.
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Greenhouse Effect
• Visible light passes
through the
atmosphere and
warms a planet’s
surface.
• The atmosphere
absorbs infrared light
from the surface,
trapping heat.
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Global Warming
• Earth’s average temperature has increased by
0.5°C in past 50 years.
• The concentration of CO2 is rising rapidly.
• An unchecked rise in greenhouse gases will
eventually lead to global warming.
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CO2 Concentration
• Most of the CO2 increase has happened in last 50
years!
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Modeling of Climate Change
• Complex models of
global warming
suggest that recent
temperature increase
is consistent with
human production
of greenhouse gases.
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Consequences of Global Warming
• Storms more numerous and intense
• Rising ocean levels; melting glaciers
• Uncertain effects on food production,
availability of fresh water
• Potential for social unrest
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What have we learned?
• What are terrestrial planets like on the inside?
– All terrestrial worlds have a core, mantle, and crust.
– Denser material is found deeper inside.
• What causes geological activity?
– Interior heat drives geological activity.
– Radioactive decay is currently main heat source.
• Why do some planetary interiors create magnetic
fields?
– Requires motion of charged particles inside a planet
© 2010 Pearson Education, Inc.
What have we learned?
• What processes shape planetary surfaces?
– Cratering, volcanism, tectonics, erosion
• How do impact craters reveal a surface’s
geological age?
– The amount of cratering tells us how long ago
a surface formed.
• Why do the terrestrial planets have
different geological histories?
– Differences arise because of planetary size,
distance from Sun, and rotation rate.
© 2010 Pearson Education, Inc.
What have we learned?
• What geological processes shaped our
Moon?
– Early cratering is still present.
– Maria resulted from volcanism.
• What geological processes shaped
Mercury?
– Had cratering and volcanism similar to Moon
– Tectonic features indicate early shrinkage.
© 2010 Pearson Education, Inc.
What have we learned?
• How did Martians invade popular culture?
– Surface features of Mars in early telescopic
photos were misinterpreted as “canals.”
• What are the major geological features of
Mars?
– Differences in cratering across surface
– Giant shield volcanoes
– Evidence of tectonic activity
© 2010 Pearson Education, Inc.
What have we learned?
• What geological evidence tells us that
water once flowed on Mars?
– Some surface features look like dry riverbeds.
– Some craters appear to be eroded.
– Rovers have found rocks that appear to have
formed in water.
– Gullies in crater walls may indicate recent
water flows.
© 2010 Pearson Education, Inc.
What have we learned?
• What are the major geological features of
Venus?
– Venus has cratering, volcanism, and tectonics
but not much erosion.
• Does Venus have plate tectonics?
– The lack of plate tectonics on Venus is a
mystery.
© 2010 Pearson Education, Inc.
What have we learned?
• How do we know that Earth’s surface is in
motion?
– Measurements of plate motions confirm the
idea of continental drift.
• How is Earth’s surface shaped by plate
tectonics?
– Plate tectonics is responsible for subduction,
seafloor spreading, mountains, rifts, and
earthquakes.
© 2010 Pearson Education, Inc.
What have we learned?
• Was Earth’s geology destined from birth?
– Many of Earth’s features are determined by
its size, distance from Sun, and rotation rate.
– The reason for plate tectonics is still a
mystery.
© 2010 Pearson Education, Inc.
© 2010 Pearson Education, Inc.