Download Chapter 20 and 21 Earth: The Active Planet Moon: Airless World

4/20/2017
Foundations of Astronomy | 13e
Seeds
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Phys1411 – Introductory Astronomy
Instructor: Dr. Goderya
© Cengage Learning 2016
Announcements/Reminders
• Exam 3: Thursday 27th April
Chapters 8, 19, 20, 21, 22
Review the question I put on the power points and the
pretest in the homework. Pretest is just for practice, I
don’t count them for grade. I may give you a small
sample question set.
Chapter 20 and 21
• Lab for this week is uploaded online: Due April 25th.
• Homework for chapter 19 due April 28th
• Homework for chapter 20 due April 28th
• Homework for chapter 21 due April 28th
• Homework for chapter 22 due April
28th
Chapter 20
1. Earth Formation
A. Layers
B. Formation
2. The Solid Earth
A. Earth's Interior
B. The Magnetic Field
C. Earth's Active Crust
Earth: The Active Planet
Moon: Airless World
Chapter 21
1. The Moon
A. The View From Earth
B. Highlands and Lowlands
C. The Apollo Missions
D. Moon Rocks
E. The History of the Moon
F. The Origin of Earth's Moon
3. The Earth’s Atmosphere
A. Origin of the Atmosphere
B. Human Effects on Earth's Atmosphere
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20-1: Formation of Earth
20-1: Formation of Earth
The four stages of
Terrestrial planet
development are illustrated
for Earth.
The four stages of Terrestrial
planet development are
illustrated for Earth.
1.Differentiation produces a
dense core, thick mantle,
and low-density crust.
2.The young Earth was
heavily bombarded in the
debris-filled early solar
system.
3.Flooding by molten rock and
later by water can fill lowlands.
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4.Slow surface evolution
continues due to geological
processes, including erosion.
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20-2: Earth: Structure and Layers
Earth’s surface is
marked by high
continents and low
seafloors. The crust
is only 10 to 60 km thick,
and interior to that are a
deep mantle and an
inner core.
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20-2: Earth’s Interior
Direct exploration of Earth’s interior (e.g. drilling) is impossible.
Earth’s interior can be explored through seismology:
earthquakes produce seismic waves.
Two types of seismic waves:
Pressure waves:
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
Earth’s interior.
Shear waves:
Particles
vibrate back
and forth
Particles
vibrate up
and down
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20-2: Seismology
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20-2: Earth’s Interior Temperature
Basic structure:
Solid crust
Solid mantle
Liquid core
Solid inner core
Earth’s interior gets hotter towards the center.
Earth’s core is as hot as the sun’s surface; metals are liquid.
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20-2: Earth’s Interior Temperature
Test Your Learning?
Basic structure:
Melting point = temperature at which an element melts (transition from solid to
liquid)
Earthquakes are an important tool for scientists
because their vibrations
a) influence the Earth's orbit about the Sun
=> Inner core
becomes solid
b) allow the study of the Earth's internal
structure
c) inform us of the mass of the Earth
d) are used to predict the future of plate
tectonics
Melting point increases with increasing pressure towards the
center
20-2: The Magnetic Field
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20-2:The Role of Earth’s Magnetic Field
• Earth’s magnetic
field is a direct
result of its rapid
rotation and its
molten metallic
core.
(a) Earth’s magnetic field dominates space around Earth by deflecting the solar
wind and trapping high-energy particles in radiation belts. The magnetic field lines
enter Earth’s atmosphere around the north and south magnetic poles. (b) Powerful
currents flow down along the magnetic field lines near the poles and excite gas
atoms to emit photons, creating auroras. Colors are produced as different atoms
are excited. Note the meteor (shooting star).
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Test Your Learning?
The Earth's magnetic dynamo is caused by a
combination of convection in its molten core and
Test Your Learning?
Particles from the Sun interact with the Earth's
magnetic fields to produce
a)
the Earth's orbit around the Sun
a)
b)
the Earth's rotation
b)
dangerous ultraviolet radiation
c)
lunar tidal action
c)
hydrogen and helium
d)
the aurora borealis
d)
protons and electrons
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the aurora borealis
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20-2: The Active Earth
20-2: Tectonic Plates
Earth’s crust is composed of several distinct tectonic plates, which
are in constant motion with respect to each other  Plate
About 2/3 of Earth’s surface is
covered by water.
tectonics
Mountains are relatively rapidly
eroded away by the forces of
water.
Evidence for plate tectonics can
be found on the ocean floor
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20-2: Plate Tectonics
… and in geologically active
regions all around the Pacific
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20-2: Active Zones Resulting from Plate Tectonics
Tectonic plates move with respect to each other.
Where plates move toward
each other, plates can be
pushed upward and downward Where plates move away
from each other, molten
 formation of mountain
lava can rise up from
ranges, some with volcanic
activity, earthquakes
below  volcanic activity
20-2: Earth’s Tectonic History
Volcanic hot spots due to
molten lava rising up at plate
boundaries or through holes in
tectonic plates
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Test Your Learning?
When two continental plates collide, the likely
result is that
a) folded mountains are created
b) a hot spot is produced
c) very young rocks emerge from below the
crust
d) a crater is formed
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20-3 - The Atmosphere
20-3 The Structure of Earth’s Atmosphere
Earth had a primeval atmosphere from remaining gasses captured
during formation of Earth
Composition of Earth’s
atmosphere is further
influenced by:
Atmospheric composition
severely altered (
secondary atmosphere)
through a combination of
two processes:
1) Outgassing: Release of
gasses bound in compounds in
the Earth’s interior through
volcanic activity
2) Later bombardment with icy
meteoroids and comets
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20-3 A Common Misconception
• Misconception: There is life on Earth
because of oxygen
– Truths:
• Oxygen was not part of Earth’s primeval
atmosphere
• There is oxygen in Earth’s atmosphere because of
life
• Photosynthesis by plants is what keeps steady
supply of oxygen in Earth’s atmosphere
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3 – B Climate and Human Effects on the
Atmosphere
(c) The concentration of CO2 in
Earth’s atmosphere as
measured in Antarctic ice cores
remained roughly constant for
thousands of years until the
beginning of the Industrial
Revolution around the year
1800. Since then it has
increased by more than 35
percent. Evidence from
proportions of carbon isotopes
and oxygen in the atmosphere
proves that most of the added
CO2 is the result of burning
fossil
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• Chemical reactions
in the oceans,
• Energetic radiation
from space (in
particular, UV)
The ozone
layer is
essential for life
on Earth since
it protects the
atmosphere
from UV
radiation
• 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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20-3 Climate and Human Effects on the
Atmosphere
The greenhouse effect:
(a) Visual-wavelength sunlight
can enter a greenhouse and
heat its contents, but the
longer-wavelength infrared
radiation cannot get out.
(b) The same process can heat
a planet’s surface if its
atmosphere contains
greenhouse gases such as
CO2 .
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Common Misconceptions
• Misconception: Greenhouse effect is bad
for Earth
– Truths:
• Earth has always had a greenhouse effect
• CO2 is not the only greenhouse gas
• Also includes water vapor, methane and other
gases
• Misconception: Ozone is bad
– Truth: The ozone layer is what protects
Earth’s surface from harmful UV radiation
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20-3 Global Warming
20-3 Global Warming (cont’d.)
• The average temperature on Earth is
increasing
– Since the 20th century, temperature rose
0.6 – 0.9°C
– Human activity (CO2 emissions and
deforestation) is drastically increasing the
concentration of greenhouse gases
• Impacting Earth’s albedo
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(a) Satellite observations of ozone concentrations over
Antarctica are shown here as red for highest concentration and
violet for lowest. Since the 1970s, a hole in the ozone layer
has developed over the South Pole. (b) Although ozone
depletion is most dramatic above the South Pole, ozone
concentrations have declined at all latitudes.
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Common Misconceptions
• Misconception: The observed warming of
Earth is result of natural causes rather
than greenhouse effect
– Truths:
• Natural causes should be driving temperatures to
decrease, not increase
Common Misconceptions (cont’d.)
• Misconception: All of Earth will warm at
same rate
– Truth:
• N. America will be warm and dry while Europe
becomes more wet and cool.
• Sun’s luminosity has remained constant
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Test Your Learning?
The greenhouse effect is caused mostly by
a)
pesticides
b)
depletion of the ozone layer
c)
carbon dioxide in the atmosphere
d)
strong magnetic field
e)
the aurora borealis
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21-1: The Moon: The View from Earth
21-1: The Moon
From Earth, we
always see the
same side of the
moon.
Moon rotates around
its axis in the same
time that it takes to
orbit around Earth:
The side of the Moon that
faces Earth is a familiar
sight. Craters have been
named for famous scientists
and philosophers, and the
so-called seas have been
given romantic names. Mare
Imbrium is the Sea of Rains,
and Mare Tranquillitatis is
the Sea of Tranquillity.
There is, in fact, no water on
the Moon.
Tidal coupling:
Earth’s gravitation has
produced tidal bulges
on the moon;
Tidal forces have
slowed rotation down to
same period as orbital
period
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21-1: Lunar Surface Features
Two dramatically
different kinds of terrain:
21-1: Impact Cratering (cont’d.)
1. A meteorite approaches the
lunar surface at high velocity.
2. On impact, the meteorite is
deformed, heated, and
vaporized.
• Highlands:
Mountainous terrain,
scarred by craters
• Lowlands: ~ 3 km lower
than highlands; smooth
surfaces:
1
Maria (pl. of mare):
Basins flooded by
lava flows
2
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21-1: Impact Cratering (cont’d.)
21-1:History of Impact Cratering
Impact Cratering
3. The resulting explosion
blasts out a round crater.
4. Slumping produces terraces
in crater walls, and rebound
can raise a central peak.
Most of the craters on
the Moon were
produced long ago
when the Solar System
was filled with debris
from planet building. As
that debris was swept
up, the cratering rate
fell rapidly.
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4
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Learning 2016
ClassAction:
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21-1: Missions to the Moon
21-1: Apollo Landing Sites (2)
Major challenges:
Need to carry enough fuel for:
• in-flight corrections,
• descent to surface,
Selected to sample
as wide a variety as
possible of different
lowland and
highland terrains.
• re-launch from the surface,
• return trip to Earth;
need to carry enough food and
other life support for ~ 1 week
for all astronauts on board.
Lowland
s (maria)
Solution:
• only land a small, light
lunar module;
• leave everything behind that
is no longer needed.
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Highlands
Lunar module (LM) of Apollo 12
on descent to the surface of the
moon
21-1: The Apollo Missions (cont’d.)
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21-1: Lunar Geology
• All lunar rocks are igneous (magma or lava)
– No sedimentary (cementing of layers) rocks
– Contain little water
– Lunar maria composed of dark, dense basalts (fine
grain volcanic rock)
– Some basalts are vesicular (cavities)
– Highlands have anathorsite rock (contains only one
major mineral)
– Highlands and lowlands are covered with regolith
(dust, soil, broken rock)
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21-1: Formation of Maria
21-1: Origin of Mare Imbrium
Lava flooding after the end of the heavy
bombardment filled a giant, multiringed
basin and formed Mare Imbrium.
1.Four billion years ago, an impact forms
a multiringed basin over 1000 km (600
mi) in diameter.
2.Continuing impacts crater the surface
but do not erase the high walls of the
multiringed basin.
(a) Much of the near side of the Moon is marked by great, generally circular lava
plains called maria. Major impacts broke the crust, and lava welled up to flood the
largest, deepest basins, forming the maria. (b) The crust on the far side is thicker,
and there is much less flooding. Even the huge Aitken Basin contains little lava
flooding. In these maps, color marks elevation, with red the highest regions and
purple the lowest.
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2
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21-1: Origin of Mare Imbrium
21-1: Origin of Mare Imbrium
3. Impacts form a few large craters,
and, starting about 3.8 billion
years ago, lava floods low regions.
4. Repeated lava flows cover most of
the inner rings and overflow the
basin to merge with other flows.
5. Impacts continue, including those
that formed the relatively young
craters Copernicus and Kepler.
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3
4
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21-1: Formation of Moon: Giant Impact Theory
Sometime before the Solar System was 50
million years old, a collision produced
Earth and the Moon in its orbit inclined to
Earth’s equator.
1.A protoplanet nearly the size of Earth
differentiates to form an iron core.
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2.Another body that has also formed an
iron core strikes the larger body and
merges, trapping most of the iron inside.
1
2
4
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21-1: Giant Impact Theory
4 - F: Giant Impact Theory
3. Iron-poor rock from the mantles
of the two bodies forms a ring of
debris.
4. Volatiles are lost to space as the
particles in the ring begin to
accrete into larger bodies.
5. Eventually the Moon forms from the
iron-poor and volatile-poor matter in
the disk.
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3
4
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Test Your Learning?
There is very little atmosphere on the Moon
because
a)
dry rocks on the Moon absorbed its own
atmosphere
b)
it was blown away by meteor
bombardment
c)
its low mass and high temperature allowed
most gases to escape
Acknowledgment
• The slides in this lecture is for Tarleton:
PHYS1411/PHYS1403 class use only
• Images and text material have been
borrowed from various sources with
appropriate citations in the slides,
including PowerPoint slides from
Seeds/Backman text that has been
adopted for class.
d)
the gravitational tidal forces from the Earth
stripped
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it away
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