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Earth as Planet
• The Earth is a medium size planet with
a diameter of 12,756 kilometers (7926
miles)
• Composed primarily of iron, silicon, and
oxygen
• Nearly circular orbit and just the right
distance from the Sun

Water not boiled away or frozen
• No hydrogen or helium in the
atmosphere

Hydrogen bound in water
ISP 205 - Astronomy Gary D. Westfall
Lecture 9
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Earth’s Interior
• The Earth’s interior has been studied using seismic
waves

Waves produced by earthquakes, impacts, explosions
• Crust
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6 km thick basalt under oceans
20 - 70 km thick granite under continents
• Mantle

Solid, extends to a depth of 2900 km
• Core
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Diameter of 7000 km, iron, nickel
• Inner core
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Diameter of 2400 km, dense and solid
ISP 205 - Astronomy Gary D. Westfall
Lecture 9
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Earth’s Magnetic Field
• Earth’s magnetic field is approximately aligned with the
•
geographic poles
The Earth’s magnetic field traps charged particles from the Sun’s
solar wind
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Magnetosphere
Causes aurora borealis
ISP 205 - Astronomy Gary D. Westfall
Lecture 9
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The Earth’s Crust
• Crust is composed of various kinds of rock
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Igneous - volcanic
Sedimentary - deposited by wind or water
Metamorphic - changed by temperature/pressure
• Primitive rock exists in the form of comets and asteroids
but not on Earth

All the material on Earth was once molten
• The crust is broken up into pieces called that float on the
mantle

Plate tectonics
ISP 205 - Astronomy Gary D. Westfall
Lecture 9
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Plate Tectonics
• Convection in the mantle causes movement of the
plates

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Plates pull apart along rift zones
Plates come together at subduction zones
ISP 205 - Astronomy Gary D. Westfall
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Results of Plate Tectonics
Liquid lava reaches the ocean in Hawaii
above a rift zone in the ocean floor
The Alps are
uplifted by the
African plate
bumping into
Europe
The San Andreas Fault,
the boundary between
the Pacific Plate and the
American Plate
ISP 205 - Astronomy Gary D. Westfall
Lecture 9
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Structure of the Earth’s Atmosphere
• The atmosphere does not have much mass compared with
•
•
the entire Earth
The atmosphere is usually divided into layers
Troposphere

Most of the atmosphere is within 10 km of the surface of the
Earth
• Stratosphere

Top of the stratosphere is the ozone
layer (O3)
• Mesosphere
• Ionosphere


Air molecules are ionized by UV
from Sun
Reflect AM and longer radio waves
ISP 205 - Astronomy Gary D. Westfall
Lecture 9
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Composition of Earth’s Atmosphere
• Earth’s atmosphere consists of


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78% nitrogen (N2)
21% oxygen (O2)
1% argon (Ar)
Traces of


water vapor (H2O)
Carbon dioxide (CO2)
• The Earth’s atmosphere today is not the same as it was
originally


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May have been formed as the Earth formed
May have been released from the interior after Earth formation
May have come from impacts of comets
Dramatically influenced by the onset of living things
ISP 205 - Astronomy Gary D. Westfall
Lecture 9
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Origin of Life and the Earth’s Atmosphere
• A key step in the evolution of life on Earth was the
development of blue-green algae
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Consumed CO2 and gave off O2
Photosynthesis
• Free O2 began accumulating in the Earth’s atmosphere
•
about 2 billion years ago
The ozone layer formed then giving protection from UV

Living things could leave the oceans
• Life and the presence of water produced a dramatic
•
decrease in CO2
Decaying living things produced the nitrogen in Earth’s
atmosphere
ISP 205 - Astronomy Gary D. Westfall
Lecture 9
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Evidence for Life 3 Billion Years Ago
• Before the Earth’s atmosphere had oxygen and the
•
resulting ozone layer that absorbs UV, all life had to exist
in the safety of the ocean
In these pictures, blue algae is fossilizes in rocks dating
back 3 billion years
ISP 205 - Astronomy Gary D. Westfall
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Weather and Climate
• Weather is caused by the uneven
heating of the Earth by the Sun
and by the rotation of the Earth
• Climate refers to long term
trends in weather
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The last ice age ended 14,000
years ago after lasting for 20,000
years
2 km thick over Boston and
extended to New York City
Shaped Michigan’s topology
ISP 205 - Astronomy Gary D. Westfall
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The Greenhouse Effect and Global Warming
• CO2 is a greenhouse gas
• Sunlight of all wavelengths passes the
atmosphere, is absorbed by the surface and
radiated as infrared
• CO2 is opaque to infrared and traps the infrared
radiation, warming the Earth
 Current greenhouse gasses warm the Earth 23C
• CO
2 is increasing due to man
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Burning of fossil fuels
Destruction of forests
• More CO2 could cause global
warming
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Complex problem
ISP 205 - Astronomy Gary D. Westfall
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CO2 in Earth’s Atmosphere
• Measured at Mauna Loa, Hawaii
CO2 measurements showing
seasonal variations and plotted
with suppressed zero
Same CO2 measurements
showing seasonal variations
and plotted without a
suppressed zero
ISP 205 - Astronomy Gary D. Westfall
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CO2 in Earth’s Atmosphere 2
• Taken from air trapped in ice in Antarctica
CO2 measurements for the past
1000 years plotted with a
suppressed zero
CO2 measurements for the past
1000 years plotted without a
suppressed zero
ISP 205 - Astronomy Gary D. Westfall
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Cosmic Influences on the Evolution of Earth
• We observe that other planets have been struck by
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•
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meteors
We observe craters on these planets
Craters on Earth are erased by the active geology and be
weather
There are 100 known craters on Earth
ISP 205 - Astronomy Gary D. Westfall
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A Large Event 65 Million Years Ago
• The map below show the location of the buried
crater from an impact event 65 million years ago
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• As we will see,
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Earth as Target
there are many
objects in the
solar system that
potentially could
collide with the
Earth
The picture on
the right shows a
computer
simulation of
what the Earth
would look like
if Comet
Shoemaker-Levy
hit the Earth near
East Lansing
ISP 205 - Astronomy Gary D. Westfall
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