Download DTU 8e Chap 6 Earth and Moon

Neil F. Comins • William J. Kaufmann III
Discovering the Universe
Ninth Edition
CHAPTER 6
Earth and the Moon
WHAT DO YOU THINK?
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6.
Can Earth’s ozone layer, which has been partially
depleted, be naturally replenished?
Who was the first person to walk on the Moon, and
when did this event occur?
Do we see all parts of the Moon’s surface at some time
throughout the lunar cycle?
Does the Moon rotate and, if so, how fast?
What causes the ocean tides?
When does the spring tide occur?
In this chapter you will discover…
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why Earth is such an ideal environment for life
that Earth is constantly in motion inside and out
how Earth’s magnetic field helps protect us
what made the craters on the Moon
how the Sun and the Moon cause Earth’s tides
that Earth and the Moon each have two (different) major
types of surface features
that water ice has been found on the Moon
Views of Earth’s Surface
An oasis in the forbidding void of space, Earth is a world of unsurpassed
beauty and variety. Ever-changing cloud patterns drift through its skies.
More than two-thirds of its surface is covered with oceans. This liquid
water, in combination with a huge variety of chemicals from its lands, led
to the formation and evolution of life over most of the planet’s surface.
The symbol is astronomers’ shorthand for “Earth.”
Temperature Profile of Earth’s Atmosphere
The atmospheric temperature changes with
altitude because of the way sunlight and heat
from Earth’s surface interact with various gases
at different heights.
The Greenhouse Effect in a Car
The glass windows in this car allow visible light to enter
but prevent the infrared radiation released by the car’s
interior from escaping. The infrared, therefore, heats
the air in the car much higher than the outside air. This
action also occurs in greenhouses and is called the
greenhouse effect.
The Greenhouse Effect
Sunlight and heat from Earth’s interior warm Earth’s
surface, which in turn radiates energy, mostly as infrared
radiation. Much of this radiation is absorbed by
atmospheric carbon dioxide and water, increasing
Earth’s temperature. In equilibrium, Earth radiates as
much energy as it receives.
The Greenhouse Effect
The amount of carbon dioxide in our atmosphere since
1000 A.D. has been determined. The increase in
carbon dioxide since 1800 due to burning fossil fuels
and decreases in forestation have caused a dramatic
temperature increase.
The surface of Earth, or
the crust, is made of
less-dense rock floating
on a layer of denser
material.
Shown here is an
artist’s rendition of one
such boundary, a
mountain range in the
middle of the ocean
floor, called the MidAtlantic Ridge.
The Supercontinent Pangaea
The present continents are pieces of what was
once a bigger, united body called Pangaea.
The Supercontinent Pangaea
Geologists believe that Pangaea must have first split
into two smaller supercontinents, which they call
Laurasia and Gondwana.
The Supercontinent Pangaea
These bodies later separated into the continents of
today. Gondwana split into Africa, South America,
Australia, and Antarctica, while Laurasia divided to
become North America and Eurasia.
Earth’s Major Tectonic Plates continue to shape
Earth
Differentiation as Earth Formed
Early Earth was initially a homogeneous mixture of
elements. (a) Molten iron sank to the center and light
material floated upward to form a crust. (b) As a result,
Earth has a dense iron core and a crust of light rock,
with a mantle of intermediate density between them.
Convection is a familiar process
Heat supplied by the heating coil warms the water at the
bottom of the pot. The heated water rises and transfers
its heat to the cooler surroundings. When the hot, rising
water gets to the top of the pot, it loses heat and sinks
back to the bottom of the pot to repeat the process.
Convection and the Mechanism of Plate Tectonics
Convection currents in Earth’s interior are responsible
for pushing around rigid plates on its crust. New crust
forms in oceanic rifts, where magma oozes upward
between separating plates. Mountain ranges and deep
oceanic trenches are formed where plates collide and
crust sometimes sinks back into the interior.
Earth’s Magnetic Field
Although Earth does not contain a bar magnet, its
rotation, combined with moving electric charges in its
core, creates a field similar to the bar magnet’s. Note
that the field is not aligned with Earth’s rotation axis.
Earth’s Magnetosphere
Earth’s magnetic field carves out a cavity in space that
excludes charged particles ejected from the Sun,
called the solar wind. Most of the particles of the solar
wind are deflected around Earth in the blue region.
Some charged particles in two huge, doughnut-shaped
rings called the Van Allen belts (in red).
The Northern Lights (Aurora Borealis)
Charged particles from the Sun can overload the Van
Allen belts and cascade toward Earth, producing auroras
that can be seen over a wide range of latitudes. Auroras
typically occur 100 to 400 km above Earth’s surface.
Northern Lights (Aurora Borealis) – side view
This is a view of an aurora from space. Part of a
space shuttle is visible at the bottom left of the picture.
The Northern Lights (Aurora Borealis)
This is the Aurora borealis in Alaska. The gorgeous
aurora seen here is mostly glowing green due to
emission by oxygen atoms in our atmosphere. Some
auroras remain stationary for hours, while others
shimmer, like curtains blowing in the wind.
Earth’s Magnetic Field
Earth’s Magnetic field is closely related to
all of the following EXCEPT:
A) Compass needles point north
B) Earth is shielded from the solar wind
C) Radiation is trapped in the Van Allen belts
D) Hurricanes rotate counterclockwise
E) The Aurora Borealis (Northern Lights)
A Microscopic Lunar Crater
This photograph, made with a microscope,
shows tiny microcraters less than 1 mm across
on a piece of Moon rock.
Mare Imbrium and the Surrounding Highlands
Mare Imbrium, the largest of the 14 dark plains that
dominate the Earth-facing side of the Moon, is ringed
by lighter-colored highlands strewn with craters and
towering mountains. The highlands were created by
asteroid impacts pushing land together.
Details of a Lunar Mare
Close-up views of the lunar maria reveal rilles and
numerous small craters
Astronaut David Scott on Hadley’s rille during
the Apollo 15 mission to the Moon.
The Far Side
of the Moon
Using a laser mounted on the Lunar Reconnaissance
Orbiter, this detailed image of the lunar far side was
made in 2010. Going by the colors of the rainbow,
violet indicates lowest terrain, while red indicates
highest.
An Apollo Astronaut on the Moon
Apollo 17 astronaut Harrison Schmitt enters the
Taurus-Littow Valley on the Moon. The enormous
boulder seen here slid down a mountain to the right of
this image, fracturing on the way.
The Moon’s surface is covered with a layer of
powdered rock and small pieces of rock. The
powdered rock is called regolith.
Mare Basalt
Anorthosite
Impact Breccias
These rocks are created from shattered debris fused
together under high temperature and pressure. Such
conditions prevail immediately following impacts of
space debris on the Moon’s surface.
Apollo 11
Landing Site
On the Moon’s Sea of Tranquility, Astronaut Buzz Aldrin
stands next to the package of equipment containing the
seismic detector. The corner reflectors are still used
today to determine the distance from Earth to the Moon.
As the Moon’s interior
shrank, the surface
settled irregularly,
creating long lines of
cliffs called scarps.
Seismic experiments
revealed that the main
regions of the Moon’s
interior mimic those of
Earth, but in different
proportions.
Water ice may exist in the
polar craters, where the
energy received from the
Sun is insufficient to melt it.
This computer
simulation shows
how the Moon
could have been
formed in a
collision between
Earth and a large
planetesimal.
The collision that created the Moon could have also
knocked Earth’s rotation axis over so that today it has
a 23½° tilt, thereby creating the seasons.
Motion of Earth-Moon System Barycenter
(a) The
paths of Earth and the Moon as their
barycenter follows an elliptical orbit around the Sun.
Synchronous Rotation of the Moon
For the Moon to keep the same side facing Earth as it
orbits our planet, the Moon must rotate on its axis at
precisely the same rate that it revolves around Earth.
Tidal Forces – Differ over an Object and Cause Tides
During new and full
moon phases, the
Sun’s gravitation boosts
the tidal bulges in the During the quarter moon
same direction as the phases, the Sun pulls the tidal
Moon, creating larger bulges in a different direction
“spring tides”.
from the Moon, diminishing the
tides. These are “neap tides.“
Lunar
Ranging
Beams of laser light are fired through three
telescopes. The light is then reflected back by the
corner reflectors on the Moon. From the time it
takes the light to reach the Moon and return to
Earth, astronomers can determine the distance to
the Moon to within a few millimeters.
Tides
The strongest tides (high highs and low
lows) occur when:
A) Full Moon
B) New Moon
C) Both Full and New Moon
D) At First and Third Quarter Moon
Summary of Key Ideas
Earth: A Dynamic, Vital World
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Earth’s atmosphere is about four-fifths nitrogen and one-fifth
oxygen. This abundance of oxygen is due to the biological
processes of life-forms on the planet.
Earth’s atmosphere is divided into layers named the
troposphere, stratosphere, mesosphere, and ionosphere.
Ozone molecules in the stratosphere absorb ultraviolet light
rays.
The outermost layer, or crust, of Earth offers clues to the
history of our planet.
Earth’s surface is divided into huge plates that move over the
upper mantle. Movement of these plates, a process called
plate tectonics, is caused by convection in the mantle. Also,
upwelling of molten material along cracks in the ocean floor
produces seafloor spreading. Plate tectonics is responsible for
most of the major features of Earth’s surface, including
mountain ranges, volcanoes, and the shapes of the continents
and oceans.
Earth: A Dynamic, Vital World
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Study of seismic waves (vibrations produced by
earthquakes) shows that Earth has a small, solid inner
core surrounded by a liquid outer core. The outer core
is surrounded by the dense mantle, which in turn is
surrounded by the thin, low-density crust. Earth’s inner
and outer cores are composed primarily of iron. The
mantle is composed of iron-rich minerals.
Earth’s magnetic field produces a magnetosphere that
surrounds the planet and deflects the solar wind.
Some charged particles from the solar wind are
trapped in two huge, doughnut-shaped rings called the
Van Allen belts. An Earthward deluge of particles from
a coronal mass ejection on the Sun can produce
exceptional auroras.
The Moon and Tides
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The Moon has heavily cratered highlands and relatively
smooth-surfaced maria. Powdered into regolith, the
anorthosite rock of the highland is brighter than the
powdered basalt of the maria.
Many lunar rock samples are solidified lava formed
largely of minerals also found in Earth rocks.
Anorthositic rock in the lunar highlands was formed
between 4.0 and 4.3 billion years ago, whereas the mare
basalts solidified between 3.1 and 3.8 billion years ago.
The Moon’s surface has undergone very little geologic
change over the past 3 billion years.
Impacts have been the only significant “weathering”
agent on the Moon; the Moon’s regolith (pulverized rock
layer) was formed by meteoritic action. Lunar rocks
brought back to Earth contain no water and are depleted
of volatile elements.
The Moon and Tides
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Frozen water has been discovered in numerous places
just below the Moon’s surface.
The collision-ejection theory of the Moon’s origin,
accepted by most astronomers, holds that the young
Earth was struck by a huge planetesimal, and debris
from this collision coalesced to form the Moon.
The Moon was molten in its early stages, and the
anorthositic crust solidified from low-density magma that
floated to the lunar surface. The mare basins were
created later by the impact of planetesimals and were
then filled with lava from the lunar interior.
Gravitational interactions between Earth and the Moon
produce tides in the oceans of Earth and set the Moon
into synchronous rotation. The Moon is moving away
from Earth, and consequently, Earth’s rotation rate is
decreasing.
Key Terms
anorthosite
capture theory
cocreation theory
collision-ejection theory
continental drift
convection
core
coronal mass ejection
crust
dynamo theory
ejecta blanket
fission theory
highlands
impact breccias
ionosphere (thermosphere)
mantle
mare (plural maria)
mare basalt
mascons
mesosphere
neap tide
northern lights (aurora
borealis)
ozone layer
planetary differentiation
plate tectonics
regolith
rille
scarps
seafloor spreading
seismic waves
seismograph
solar wind
southern lights (aurora
australis)
spring tide
stratosphere
synchronous rotation
troposphere
Van Allen radiation belts
WHAT DID YOU THINK?
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Can Earth’s ozone layer, which has been partially
depleted, be naturally replenished?
Yes. Ozone is created continuously from normal oxygen
molecules by their interaction with the Sun’s ultraviolet
radiation.
WHAT DID YOU THINK?
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Who was the first person to walk on the Moon, and when
did this event occur?
Neil Armstrong was the first person to set foot on the
Moon. He and Buzz Aldrin flew on the Apollo 11
spacecraft piloted by Michael Collins. Armstrong and
Aldrin set down the Eagle Lander on the Moon on
July 20, 1969.
WHAT DID YOU THINK?
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Do we see all parts of the Moon’s surface at some time
throughout the lunar cycle?
No. Because the Moon’s rotation around Earth is
synchronous, we always see the same side. The far side
of the Moon has been seen only from spacecraft that
pass or orbit it.
WHAT DID YOU THINK?
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Does the Moon rotate and, if so, how fast?
The Moon rotates at the same rate that it revolves
around Earth, once every 27.3 days. If the Moon did not
rotate, then, as it revolved, we would see its entire
surface from Earth, which we do not.
WHAT DID YOU THINK?
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What causes the ocean tides?
The tides are created by gravitational forces from the
Moon and Sun combined with Earth’s motion around the
barycenter.
WHAT DID YOU THINK?
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When does the spring tide occur?
Spring tides occur during each full and new Moon.