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Title: The Milky Way Author: Markus Boettcher Last modified by: Brewer, Sonja Dion Created Date: 2/23/2003 4:28:17 AM Document presentation format – PowerPoint PPT presentation

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Title: Note that the following lectures include animations and PowerPoint effects such as fly ins and transitions that require you to be in PowerPoint's Slide Show mode (presentation mode).


1
Note that the following lectures include
animations and PowerPoint effects such as fly ins
and transitions that require you to be in
PowerPoint's Slide Show mode (presentation mode).
2
Planet Earth
  • Chapter 20

3
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
4
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.
5
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
6
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
7
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
8
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.
9
Seismic Waves
(SLIDESHOW MODE ONLY)
10
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
11
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

12
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
13
The Aurora (Polar Light)
As high-energy particles leak into the lower
magnetosphere, they excite molecules near the
Earths magnetic poles, causing the aurora
14
The Active Earth
About 2/3 of Earths surface is covered by water.
Mountains are relatively rapidly eroded away by
the forces of water.
15
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
16
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
17
Active Zones Resulting from Plate Tectonics
Volcanic hot spots due to molten lava rising up
at plate boundaries or through holes in tectonic
plates
18
Earths Tectonic History
19
History of Geological Activity
Surface formations visible today have emerged
only very recently compared to the age of Earth.
20
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
21
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
22
Planetary Atmospheres
(SLIDESHOW MODE ONLY)
23
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.
24
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!

25
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!
26
New Terms
comparative planetology seismic
waves seismograph pressure (P) waves shear (S)
waves mantle plastic bow shock magnetosphere Van
Allen belts plate tectonics midocean
rise subduction zone basalt folded mountain
range rift valley primeval atmosphere secondary
atmosphere
ozone layer albedo greenhouse effect global
warming
27
Discussion Questions
1. If we visited a planet in another solar system
and discovered oxygen in its atmosphere, what
might we guess about its surface? 2. If liquid
water is rare on the surface of planets, then
most terrestrial planets must have CO2-rich
atmospheres. Why?
28
Quiz Questions
1. What do we call the study of planets through
contrast and comparison? a. Geology. b.
Planetary Science. c. Contrastive Planetology. d.
Comparative Planetology. e. None of the above.
29
Quiz Questions
2. When Earth formed it melted and
differentiated. What was the source of heat that
melted Earth? a. The infall of matter that
formed Earth. b. The decay of radioactive
elements. c. Sunlight striking Earth's
surface. d. Both a and b above. e. All of the
above.
30
Quiz Questions
3. With a small telescope we see that the Moon
has regions that are relatively smooth, and
others that are saturated with impact craters.
What does this tell us about the Moon's
development? a. The Moon never went through the
differentiation stage. b. The Moon never
experienced surface flooding by lava. c. The Moon
doesn't have much slow surface evolution. d. Both
a and b above. e. All of the above.
31
Quiz Questions
4. Earth's interior can be divided up into four
zones the inner core, the outer core, the
mantle, and the crust. Which of these zones has
the lowest density? a. The inner core. b. The
outer core. c. The mantle. d. The crust. e. All
four zones have the same density.
32
Quiz Questions
5. What evidence do we have that Earth
differentiated? a. The curved paths of seismic
waves indicate that the interior density of Earth
is greater than can be explained by compression
alone. b. Deep wells have brought up iron
fragments of Earth's core. c. Diamond miners have
to endure high temperatures in deep mines. d. The
Earth-Moon system has a lot of angular
momentum. e. Aristotle's theory of the four
elements requires this to be the case.
33
Quiz Questions
6. How do P waves and S waves differ? a. P waves
oscillate parallel to their direction of travel,
whereas S waves oscillate perpendicular to their
direction of travel. b. P waves can pass through
liquids, whereas S waves cannot. c. S waves can
pass through liquids, whereas P waves cannot. d.
Both a and b above. e. Both a and c above.
34
Quiz Questions
7. How does temperature and pressure vary with
depth deep inside Earth? a. Temperature and
pressure both increase with depth. b. Temperature
and pressure both decrease with depth. c.
Temperature increases with depth, and pressure
decreases with depth. d. Temperature decreases
with depth, and pressure increases with depth. e.
Temperature and pressure do not vary with depth
inside the Earth.
35
Quiz Questions
8. What distinguishes Earth's inner core from its
outer core? a. The inner core is rock and the
outer core is iron-nickel. b. The inner core is
iron-nickel and the outer core is rock. c. The
inner core is liquid and the outer core is
solid. d. The inner core is solid and the outer
core is liquid. e. Both b and d above.
36
Quiz Questions
9. What creates Earth's strong dipole magnetic
field? a. The attractive force between massive
particles. b. The conduction of solar wind
particles through solid Earth. c. The conduction
of solar wind particles around Earth's
ionosphere. d. The Sun's magnetic field induces
an opposing magnetic field in Earth. e.
Convection in Earth's outer liquid iron-nickel
core, combined with Earth's rotation.
37
Quiz Questions
10. What erases the impact craters on Earth and
is responsible for most of the landforms that we
see? a. Plate tectonics. b. Water and ice
erosion. c. Erosion by the solar wind. d. Both a
and b above. e. Both b and c above.
38
Quiz Questions
11. What evidence do we have that Earth's outer
core is a metallic liquid? a. Volcanic activity
at Earth's surface. b. S waves are blocked,
resulting in an S-wave shadow zone. c. Earth has
a strong magnetic field. d. Both a and b
above. e. Both b and c above.
39
Quiz Questions
12. What drives the moving plates of Earth's
crust? a. Convection in Earth's outer liquid
iron core. b. Convection in Earth's rocky
mantle. c. The Moon's tidal force. d. Both a and
b above. e. Both b and c above.
40
Quiz Questions
13. Where are deep ocean trenches located
relative to the moving plates of Earth's
crust? a. Along the midocean rises. b. At
subduction zones. c. Along strike-slip
boundaries. d. Both a and b above. e. All of the
above.
41
Quiz Questions
14. Where on Earth are two plates being pushed
apart, creating new crust? a. Along the center
of the Atlantic Ocean. b. Along the center of the
Red Sea. c. Along the Indian plate / Asian plate
boundary. d. Both a and b above. e. All of the
above.
42
Quiz Questions
15. What type of tectonic zone is responsible for
the Andes Mountains that are located all along
the western side of South America? a. A midocean
rise. b. A subduction zone. c. A strike-slip
zone. d. The convergence of two continental
plates. e. None of the above.
43
Quiz Questions
16. What is the likely source of Earth's early
atmosphere that consisted of carbon dioxide and
water vapor? a. It was outgassed from Earth's
interior during volcanic activity. b. It arrived
in the form of icy planetesimals that impacted
Earth. c. These two gases are the products of
radioactive decay of long-lived radioactive
elements in Earth's crust. d. Both a and b
above. e. None of the above.
44
Quiz Questions
17. What happened to the majority of the carbon
dioxide that was formerly in Earth's
atmosphere? a. Most of it remains in the
atmosphere today. b. Most of it resides in
living plants and animals. c. Most was ionized
and eroded away by the intense solar wind of the
youthful Sun. d. Most was dissociated by
ultraviolet photons, and the carbon and oxygen
escaped into space. e. Most of it dissolved into
the oceans and now is in the form of limestone
rocks of Earth's crust.
45
Quiz Questions
18. What adverse affect is human activity having
on today's atmosphere? a. By burning coal, oil,
and natural gas deposits we are increasing the
carbon dioxide content of the atmosphere. b. By
cutting down woodlands, we are increasing the
amount of carbon dioxide in the atmosphere. c. We
are releasing chlorofluorocarbons, a gas that
breaks down ozone molecules, into the atmosphere.
d. Both a and b above. e. All of the above.
46
Quiz Questions
19. Why would a decrease in the density of the
ozone layer cause public health problems? a.
Humans need ozone, which is oxygen, for
respiration. b. Ozone is used in refrigerators to
reduce bacteria levels in food. c. The ozone
layer blocks ultraviolet light from the Sun, and
ultraviolet light causes skin cancer. d. Both a
and b above. e. All of the above.
47
Quiz Questions
20. The 2000 US presidential election depended on
the results in the state of Florida, a state
entirely less than 80 feet above sea level. In
the end the environmental candidate, Al Gore,
lost the election. Thus carbon dioxide continues
to be added to the atmosphere at a high rate.
Why should Floridians be concerned with what
might called, "Gore's Revenge"? a. Carbon
dioxide is a greenhouse gas. b. The greenhouse
effect occurs when atmospheric gases allow
visible sunlight to penetrate and hinder the
escape of infrared radiation released from a
planet's surface. c. The greenhouse effect raises
the temperature near the surface of a planet. d.
If Earth's polar ice caps melt, sea level will
rise a few hundred feet. e. All of the above.
48
Answers
1. d 2. d 3. c 4. d 5. a 6. d 7. a 8. d 9. e 10. d
11. e 12. b 13. b 14. d 15. b 16. d 17. e 18. e 19
. c 20. e
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