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Chapter Two
A Living Planet
Space and the Universe
• If you look at the sky on a clear night, you
can see thousands of stars. With a
telescope you can see millions. Beyond
that exist trillions. All of these stars are
part of the universe.
• The universe is made up of all existing
things, including space and Earth.
Space and the Universe
• Most
astronomers
believe that the
universe has
been
expanding
continuously to
an
unimaginable
size.
The Solar System
• The Sun and
the group of
bodies that
revolve around
it are called the
Solar System.
Earth’s Zones
• Scientist have identified four major zones in
Earth’s interior.
• The planet’s center is like a nuclear furnace,
where decaying radioactive elements generate
heat.
• Earth’s center, or core, both temperatures and
pressures are very high.
• The core is divided into inner and outer layers.
The inner core is solid.
• The outer core is mostly dense liquid metal,
mainly iron and nickel.
Earth’s Core
• Beyond the core
is the mantle, the
zone that has
most of Earth’s
mass.
• The upper-most
layer is the crust.
• Although it is up
to 25 miles thick,
the crust is
comparatively
thin.
Magma
• Huge currents
carry heat from
the core through
the mantle to the
crust.
• Liquid rock
within the earth
is called magma.
Lava
• When liquid
rock spills out
into the surface
it is called lava.
• Magma erupts
from vents
called
volcanoes.
The Earth System
• OBJECTIVES:
• Describe Earth’s four
spheres.
• Describe how earth’s
environment is unique in
the solar system.
Key Terms
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Atmosphere
Lithosphere
Hydrosphere
Biosphere
Environment
The Earth’s Four Spheres
• The geographers divide the earth system
into four major parts. Each part is called a
sphere because it occupies a shell around
the planet.
• These four spheres are the atmosphere,
lithosphere, hydrosphere, and
biosphere.
Atmosphere
• The atmosphere is
the envelope of
gases that
surrounds Earth.
• It is the least dense
and outermost
sphere, extending
from Earth’s surface
to space.
Atmosphere
• Earth’s gravity holds the atmosphere around
the planet.
• About 78% of Earth’s atmosphere is a gas called
nitrogen, and about 21% oxygen. The rest is
made up of carbon dioxide ozone, and other
gases.
• These gases and water vapor sustain life on
Earth.
• The atmosphere also protects the planet from
the sun’s harmful radiation.
The atmosphere also protects the planet from the Sun’s
harmful radiation.
Lithosphere
• The lithosphere is
the solid crust of the
planet.
• This outer crust
includes rocks and
soil.
• It forms Earth’s
continents, islands,
and ocean floor.
Hydrosphere
• The
hydrosphere
is all of the
Earth’s water.
• Water covers
about 70% of
the Earth’s
surface.
The hydrosphere includes water in liquid, solid, and
gaseous forms. Liquid water is found in the oceans, lakes,
rivers, and underground. Clouds and fog are made up of
liquid droplets. Solid water, or ice, is found on both land
and sea.
The biosphere is the part of Earth that includes all life forms. It
includes all planets and animals. The biosphere overlaps the other
three spheres. It extends from deep ocean floors to high in the
atmosphere.
Four Spheres
• Earth’s four major spheres are all
interconnected. Each one affects the other.
The hydrosphere supplies people with water. It
is also home for plants and animals.
• The hydrosphere effects the lithosphere when
rain breaks up rocks and washes them away.
• It also constantly interacts with the atmosphere,
causing clouds and rain.
Section Two
The Hydrosphere
• Water is necessary for
life, but 97% of the world’s
water is too salty for most
uses. The process of
removing the salt in water
is called desalinization.
Countries dominated by
deserts use this process
to get freshwater, but it is
very expensive. Less
than 3% of the world’s
water is drinkable, and
most of that is frozen in
glaciers and the ice caps.
Hydrologic Cycle
• The amount of water on Earth stays much the
same over time. But its physical state is always
changing from gas to liquid to solid.
• The movement of water through the
hydrosphere is called the hydrologic cycle.
• Solar energy, winds, and gravity drive the
cycle. When water is heated by solar energy it
may change to vapor. This is called
evaporation.
Hydrologic Cycle
• Most water in the atmosphere has
evaporated from the ocean.
• As water vapor rises, it cools and forms
tiny droplets in a process called
condensation. These droplets join to form
clouds. They then grow to become rain
drops heavy enough to fall to Earth.
Precipitation
• Water falling to Earth (such as rain,
snow, or hail) is called precipitation.
• If it falls on land, it is stored in plants,
in a river, a lake, or below the
ground.
• Surface water either flows to the sea
in a river or it evaporates again into
the atmosphere.
The Hydrologic Cycle
• As precipitation falls on continents and islands,
it flows down hills and mountains toward the
lowlands and coasts. The first and smallest
streams from this runoff are called headwaters.
• As these
headwaters join,
they form larger
streams, and farther
downstream they
eventually form
rivers. Any smaller
stream or river that
flows into a larger
river is called a
tributary.
• In the U. S. the
Arkansas, Missouri,
and Ohio Rivers are
major tributaries of
the Mississippi
River.
Tributary
Continental Shelves
• The continental surface extends under the
shallow ocean water around the continents.
These areas are called continental shelves. At
the edges of the continental shelves, the
seafloor drops steeply down to the abyssal
plain.
Plate Tectonics
• The theory of plate
tectonics explains how
forces within the planet
create landforms.
• The tectonics theory
views Earth’s crust as
divided into more than a
dozen rigid, slow moving
plates. The plates can
be compared to the
cracked shell of a hard
boiled egg.
Pangaea
• Scientist believe
that about 200
million years ago
all of the modern
continent were
part of one
supercontinent
called Pangaea.
• The plates slowly move across the upper mantle,
usually less than an inch per year. This process is
called continental drift. Along the plate boundaries, the
crust is subject to stresses that lead to melting, bending,
and breaking.
• Volcanoes often form long rows and signal that a
plate boundary is nearby. Earthquakes take
place when tectonic forces cause masses of rock
inside the crust to break.
Plate Movement
• Three types of movement at plate boundaries
are possible. First, the plates can move apart,
or spread. The second plate movement occurs
when plates collide. The third way plates move
is laterally when they slip past each other.
Divergent Plate Movement
• Long ago the Earth’s history the crust sorted itself into
layers of different kinds of rocks. The lower layer, made
of heavier rock, is found on the ocean floor. Lying on
top is a patchy layer of lighter rock. This layer makes up
the continents.
• Earthquakes are also common near plate
boundaries.
Subduction Zones
• When two plates on the ocean floor collide, one
slides underneath the other.
• This plate boundary is called a subduction
zone, and the deep valley marking the plate
collision is called a trench.
• The plate sliding downward generates heat as it
grinds against the plate above it.
• This heat may produce a row of volcanoes
which rise enough to become islands.
Convergent Plate Movement
• Convergent plate boundaries are locations where
lithospheric plates are moving towards one another. The
plate collisions that occur in these areas can produce
earthquakes, volcanic activity, and crustal
deformation.
Transform Plate Movement
• Transform plate
boundaries are
locations where two
plates slide past one
another. The fracture
zone that forms a
transform plate
boundary is known as
a transform fault.
Most transform faults
are found in the
ocean basin and
connect offsets in the
mid-ocean ridges.
Plates Moving Laterally
• When plates move laterally past each
other, long fractures develop along the
edges of both plates. The pressure along
these boundaries is seldom uniform.
While squeezing produces low mountains,
a little spreading generates broad valleys.
Earthquakes can be frequent in these
areas. The San Andreas Fault is and
example of this.
Rift Valleys
• A few spreading plate
boundaries lie under
continents.
• In these places, the
crust stretches until it
breaks, forming rift
valleys.
• The biggest rift valleys
are in eastern Africa.
Rift Valley
• This is an example
of a rift valley in
Kenya. Note the
recessive line due to
crust separation.
• Would this be a
suitable location
build permanent
structures?
Weathering and Erosion
• Rocks break and
decay over time in
a process called
weathering.
• Weathering is
usually slow and
difficult to detect.
However, even the
hardest rock will
eventually wear
down.
Chemical Weathering
• Chemical
processes cause
some weathering.
• Substances in the
air and water react
with the rocks,
creating acids and
slowly dissolving
the rock.
Weathering
• Weathering is also caused by physical
processes that break rocks into smaller pieces.
• In high mountains repeated freezing and
thawing of water inside a cracked rock can
cause it to break even more.
• The roots of trees can pry rocks apart.
• Weathering breaks rocks into smaller particles of
gravel, sand, and mud called sediment.
Erosion
• Along with
weathering, the
other process
changing
landforms on
earth’s surface is
erosion.
• Erosion is the
movement of
surface material
from one location
to another.
Erosion
• Water, wind, and ice can cause erosion. What
types of erosion are at work?
Water, Waves, and Wind
• Water is the most
important force of erosion.
Rainfall can cause rapid
erosion where few plants
protect the ground.
• Water erosion can begin as
tiny channels on hillsides.
If erosion is severe, a
channel may grow into a
gully.
• Running water can even
carve deep canyons, such
as the Grand Canyon.
Water Erosion
• Wave action is
another powerful
force of erosion.
During a storm,
waves can tear away
tons of beach sand
within a few hours.
Waves can slowly
change shorelines
over many years.
Wind Erosion
• Wind is another force that causes erosion.
• Plants protect most land surfaces from
wind action.
• However, in dry lands, on beaches, and in
places where people or animals have
destroyed the vegetation, wind can
cause significant erosion.