Earth

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CHAPTER 6 Earth and Moon
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WHAT DO YOU THINK?

• Can the Earths ozone layer, which is now being
  depleted, be replenished?
• Who was the first person to walk on the Moon and
  when did this event occur?
• Do we see all parts of the Moons 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?

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• You will discover
• why the Earth is such an ideal environment for
  life
• that the Earth is constantly in motion, both
  inside and out
• how Earths magnetic field helps protect us
• what made the craters on the Moon
• how the Sun and Moon cause the Earths tides
• that both the Earth and Moon have two (different)
  major types of surface features
• that water ice may have been found at the Moons
  poles

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Temperature Profile of Earths Atmosphere
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The surface of the Earth, or crust, is made of
less dense rock floating on a layer of denser
material. The crust has distinct boundaries,
indicating that the continents are separate
bodies. Shown here is an artist conception of one
such boundary, a mountain range in the middle of
the ocean floor called the Mid-Atlantic Ridge.
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Continental Drift
The continents shift and move slowly over time.
At one point, the continents are believed to
have been together, in the form of a
supercontinent called Pangaea. This
supercontinent then separated into smaller
continental plates. Some plates separated
further, creating mid-oceanic ridges, while
others collided, creating large mountain ranges.
Eventually the familiar continents of today
emerged.
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The boundaries of Earths tectonic plates show
different motions
Colliding
Separating
Sliding past one another
The Earths Major Tectonic Plates
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Differentiation as the Earth Formed
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Convection currents are created when a heat
source raises the temperature at the bottom of a
liquid or gas, as in a pot of boiling water.
Convection currents in the Earths liquid magma
just underneath the crust are responsible for the
movement of the continental plates.
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Earth is surrounded by a magnetic field believed
to be produced by convection in its molten iron
core.
The magnetic field produced is similar to that of
a bar magnet.
The axis of the Earths magnetic field differs
from the axis of rotation by 11, placing the
north magnetic pole in a different location than
the geographic (true) North Pole.
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The Earths Magnetic Field Protects us from the
Solar Wind
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Near the magnetic poles, these particles
sometimes leak into our atmosphere, causing the
gases to glow. This is known as the aurora.
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The most obvious feature on the Moons surface
are its many craters. Most of the Moons craters
are round, implying that they were formed from
impacts by high-speed meteoroids. Craters
include features such as central peaks, collapsed
terrace walls, and ejecta blankets.
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Close examination of moon rocks reveal tiny
microcraters less than one millimeter in
diameter.
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The Moons surface also has large, dark gray
plains called maria. Since these regions have
few impact craters, the lunar surface here is
relatively young compared with the lighter
surrounding terrain.
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From Earth, maria appear to be smooth regions on
the lunar surface. However, close-up photographs
reveal small craters and occasional cracks called
rilles.
CLOSE-UP VIEWS FROM A LUNAR ORBITER
APOLLO 15 MISSION
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A surprising find from lunar orbiters is that the
side of the Moon facing away from the Earth has
only one small mare, while the rest is covered
with craters.
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Missions to the Moon have revealed much about its
history.
The Moons surface is covered with a layer of
powdered rock called regolith.
An enormous boulder fractured while sliding down
a mountain
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Lunar Rocks from Different Regions
MARE BASALT contains many holes, suggesting that
gas was dissolved in the lava and solidified to
create this rock.
ANORTHOSITE from the highlands is an ancient rock
believed to be part of the Moons original crust.
IMPACT BRECCIAS are created from debris fused
together under high temperature and pressure
created by impacts of space debris with the lunar
surface.
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Seismic experiments revealed that the main
regions of the Moons interior mimic those of the
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.
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The similarity in materials making up the Earth
and Moon suggest that the Moon may have been
created from Earth material ejected after a
collision with a large planetesimal.
MOON
This computer simulation shows how the Moon could
have been formed in a collision between the Earth
and a large planetesimal.
EARTH
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The Earth and Moon orbit around their center of
mass, called the barycenter.
A wrench sliding across a table rotates around
its center of mass.
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Gravitational forces have locked the Moon into a
synchronous rotation in which the Moons orbital
period around the Earth is equal to the
rotational period of its axis. As a result, the
same side of the Moon always faces the Earth.
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Gravitational forces of the Moon on the Earth and
its oceans create tidal bulges on both sides of
the Earth.
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During new and full moon phases, the Suns
gravitation boosts the tidal bulges in the same
direction as the Moon, creating larger spring
tides.
During the quarter moon phases, the Sun pulls the
tidal bulges in a different direction from the
Moon, diminishing the tides. These are called
neap tides.
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Frictional forces between the Earths oceans and
the ocean floor keep the bulge ahead of the Moon
by 10 degrees. Gravity between the bulge and
the Moon pull it forward. As a result, the Moon
is spiraling away from the Earth at a rate of
3.8cm per year. The energy given to the Moon
comes from the Earths rotation, which is slowed
in the process.
Laser beams fired at the Moon bounce off
reflectors placed by Apollo astronauts and return
to Earth. By timing this process, we can
determine the distance to the Moon within a few
millimeters.
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WHAT DID YOU THINK?

• Can the Earths ozone layer, which is now being
  depleted, be replenished?
• Yes ozone is created continuously.
• Who was the first person to walk on the Moon and
  when did this event occur?
• Neil Armstrong on July 20, 1969
• Do we see all parts of the Moons surface at some
  time throughout the lunar cycle?
• No because the Moons rotation around Earth is
  synchronous, we always see the same side.

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WHAT DID YOU THINK?

• Does the Moon rotate and, if so, how fast?
• Yes, the Moon rotates at the same rate that it
  revolves around the Earth.
• What causes the ocean tides?
• They are created by orbital and gravitational
  forces, primarily from the Moon and, to a lesser
  extent, the Sun.
• When does the spring tide occur?
• Twice monthly, during each full and new Moon.

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Key Terms
regolith rille seafloor spreading seismic
waves seismograph solar wind southern lights
(aurora Australis) spring tide stratosphere synchr
onous rotation tidal force troposphere Van Allen
radiation belts
impact breccias ionosphere magnetosphere mantle ma
re (plural maria) mare basalt mascons mesosphere n
eap tide northern lights (aurora borealis) ozone
layer planetary differentiation plate tectonics
anorthosite capture theory cocreation
theory collision-ejection theory continental
drift convection core coronal mass
ejection crust dynamo theory ejecta
blanket fission theory highlands