Planet Earth

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Planet Earth

• Chapter 20

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Guidepost
Astronomy has been described as the science of
everything above the clouds. Planetary
astronomers, however, must also think about what
lies below the clouds because Earth is the basis
for comparison with all other Earthlike planets.
We know Earth well, and we can apply what we know
about Earth to other worlds. There is another
reason for studying Earth in an astronomy course.
Astronomy is really about us. Astronomy is
exciting and fascinating because it helps us
understand what we are and where we are in the
universe. Thus, we cannot omit Earth from our
discussionit is where we are. The next two
chapters will discuss the Earthlike planets, but
that will not end our thoughts of Earth. The
moons of
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Guidepost (continued)
the giant outer worlds will seem Earthlike in
strange ways, and our discussion of the smaller
bodies of our solar system will alert us to the
dangers Earth faces. Throughout the rest of this
book, we will remain painfully aware of the
fragile beauty of our planet.
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Outline
I. The Early History of Earth A. Four Stages of
Planetary Development B. Earth as a Planet II.
The Solid Earth A. Earth's Interior B. The
Magnetic Field C. Earth's Active Crust III. The
Atmosphere A. Origin of the Atmosphere B. Human
Effects on Earth's Atmosphere
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The Early History of Earth
Earth formed 4.6 billion years ago from the inner
solar nebula.
Four main stages of evolution
Two sources of heat in Earths interior

• Potential energy of infalling material

• Decay of radioactive material

Most traces of bombardment (impact craters) now
destroyed by later geological activity
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Earths Interior
Direct exploration of Earths interior (e.g.
drilling) is impossible.
Earths interior can be explored through
seismology
earthquakes produce seismic waves.
Two types of seismic waves
Pressure waves
Shear waves
Particles vibrate back and forth
Particles vibrate up and down
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Seismology
Seismic waves do not travel through Earth in
straight lines or at constant speed.
They are bent by or bounce off transitions
between different materials or different
densities or temperatures.
Such information can be analyzed to infer the
structure of Earths interior.
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Seismic Waves
(SLIDESHOW MODE ONLY)
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Earths Interior (2)
Basic structure
Earths interior gets hotter towards the center.
Earths core is as hot as the suns surface
metals are liquid.
Melting point increases with increasing pressure
towards the center
Melting point temperature at which an element
melts (transition from solid to liquid)
gt Inner core becomes solid
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Earths Magnetic Field

• Earths core consists mostly of iron nickel
  high electrical conductivity

• Convective motions and rotation of the core
  generate a dipole magnetic field

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The Role of Earths Magnetic Field
Earths magnetic field protects Earth from
high-energy particles coming from the sun (solar
wind).
Surface of first interaction of solar wind with
Earths magnetic field Bow shock
Region where Earths magnetic field dominates
magnetosphere
Some high-energy particles leak through the
magnetic field and produce a belt of high-energy
particles around Earth Van Allen belts
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The Aurora (Polar Light)
As high-energy particles leak into the lower
magnetosphere, they excite molecules near the
Earths magnetic poles, causing the aurora
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The Active Earth
About 2/3 of Earths surface is covered by water.
Mountains are relatively rapidly eroded away by
the forces of water.
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Tectonic Plates
Earths crust is composed of several distinct
tectonic plates, which are in constant motion
with respect to each other ? Plate tectonics
Evidence for plate tectonics can be found on the
ocean floor
and in geologically active regions all around
the Pacific
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Plate Tectonics
Tectonic plates move with respect to each other.
Where plates move toward each other, plates can
be pushed upward and downward ? formation of
mountain ranges, some with volcanic activity,
earthquakes
Where plates move away from each other, molten
lava can rise up from below ? volcanic activity
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Active Zones Resulting from Plate Tectonics
Volcanic hot spots due to molten lava rising up
at plate boundaries or through holes in tectonic
plates
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Earths Tectonic History
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History of Geological Activity
Surface formations visible today have emerged
only very recently compared to the age of Earth.
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Earths atmosphere

• Layer of gasses surrounding the Earth held in
  place by gravity
• Shields the suns ultraviolet rays
• Retains heat (greenhouse effect
• Reduces temperature extremes between day and night

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Earths Atmosphere consists of four major layers

• Top layer is the Exosphere which includes the
  magnetosphere but not counted among the major
  layers
• Most of our weather happens in the troposphere.
  80 of total mass of atmosphere. 8-16 km deep.
• In stratosphere, about 25 km from the surface of
  the Earth is the ozone layer which protects the
  Earth from most of the Suns harmful UV rays.
  Lower portion is influenced by jet streams
• Mesosphere has coldest temperatures of about
  -90C
• Thermosphere has greatest temperature range from
  -90 - 1200 C

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The Ionosphere

• Layer that stretches between the lower mesosphere
  and into the exosphere, running contiguously with
  the thermosphere.
• 4 levels that reflect different types of radio
  waves
• D from 60-80 km reflects radio waves
• E from 80-120 km reflects short wave
• F1 around 170km
• F2 roughly from 250-300km

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The Atmosphere
Earth had a primeval atmosphere from remaining
gasses captured during formation of Earth
Atmospheric composition severely altered (?
secondary atmosphere) through a combination of
two processes
1) Outgassing Release of gasses bound in
compounds in the Earths interior through
volcanic activity
2) Later bombardment with icy meteoroids and
comets
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1. In which layer of the atmosphere does the
weather occur?

• Mesosphere
• Troposphere
• Thermosphere
• Stratosphere

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1. In which layer of the atmosphere does the
weather occur?

• Mesosphere
• Troposphere
• Thermosphere
• Stratosphere

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2. A little less than 20 of the atmospheres
mass is in the __

• Stratosphere
• Troposphere
• Mesosphere
• Thermosphere

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2. A little less than 20 of the atmospheres
mass is in the __

• Stratosphere
• Troposphere
• Mesosphere
• Thermosphere

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3. The greatest atmospheric temperature range is
found in the

1. Stratosphere
2. Troposphere
3. Mesosphere
4. Thermosphere

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3. The greatest atmospheric temperature range is
found in the

1. Stratosphere
2. Troposphere
3. Mesosphere
4. Thermosphere

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4. The primary gases in the atmosphere are

1. Nitrogen, oxygen, carbon dioxide
2. Nitrogen, oxygen, argon
3. Carbon dioxide, nitrogen, argon
4. Carbon dioxide, argon, water vapor

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4. The primary gases in the atmosphere are

1. Nitrogen, oxygen, carbon dioxide
2. Nitrogen, oxygen, argon
3. Carbon dioxide, nitrogen, argon
4. Carbon dioxide, argon, water vapor

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The Structure of Earths Atmosphere
Composition of Earths atmosphere is further
influenced by
The ozone layer is essential for life on Earth
since it protects the atmosphere from UV radiation

• Chemical reactions in the oceans,

• Energetic radiation from space (in particular,
  UV)

• Presence of life on Earth

The temperature of the atmosphere depends
critically on its albedo percentage of sun
light that it reflects back into space
Depends on many factors, e.g., abundance of water
vapor in the atmosphere
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Human Effects on Earths Atmosphere
1) The Greenhouse Effect
Earths surface is heated by the suns radiation.
Heat energy is re-radiated from Earths surface
as infrared radiation.
CO2, but also other gases in the atmosphere,
absorb infrared light
? Heat is trapped in the atmosphere.
This is the Greenhouse Effect.
The Greenhouse Effect occurs naturally and is
essential to maintain a comfortable temperature
on Earth,
but human activity, in particular CO2 emissions
from cars and industrial plants, is drastically
increasing the concentration of greenhouse gases.
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Global Warming

• Human activity (CO2 emissions deforestation) is
  drastically increasing the concentration of
  greenhouse gases.

• As a consequence, beyond any reasonable doubt,
  the average temperature on Earth is increasing.

• This is called Global Warming

• Leads to melting of glaciers and polar ice caps
  (? rising sea water levels) and global climate
  changes, which could ultimately make Earth unfit
  for human life!

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Human Effects on the Atmosphere (2)
2) Destruction of the Ozone Layer
Ozone ( O3) absorbs UV radiation, (which has
damaging effects on human and animal tissue).
Chlorofluorocarbons (CFCs) (used, e.g., in
industrial processes, refrigeration and air
conditioning) destroy the Ozone layer.
Destruction of the ozone layer as a consequence
of human activity is proven (e.g., growing ozone
hole above the Antarctic)
Must be stopped and reversed by reducing CFC use,
especially in developed countries!
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5. Primeval atmosphere was probably altered most
by

1. The suns solar waves
2. Dinosaurs
3. Outgassing and impacts from meteors and comets
4. Space junk

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5. Primeval atmosphere was probably altered most
by

1. The suns solar waves
2. Dinosaurs
3. Outgassing and impacts from meteors and comets
4. Space junk

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6. Global warming is caused by

1. Car exhaust and deforestation
2. Carbon dioxide emissions and deforestation
3. Politicians
4. Industrial waste and deforestation

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6. Global warming is caused by

1. Car exhaust and deforestation
2. Carbon dioxide emissions and deforestation
3. Politicians
4. Industrial waste and deforestation

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7. The greenhouse effect is caused by

1. Suns heat reflected from the surface trapped by
   carbon dioxide and methane
2. Heat caused by human activity like cars,
   factories, etc.
3. The effect of a dome over the Earths atmosphere
   trapping heat
4. Mars

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7. The greenhouse effect is caused by

1. Suns heat reflected from the surface trapped by
   carbon dioxide and methane
2. Heat caused by human activity like cars,
   factories, etc.
3. The effect of a dome over the Earths atmosphere
   trapping heat
4. Mars