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Planet Earth
Our Solar System
• Earth is part of a large physical system containing
countless objects, all of which revolve around the
• Eight spheres, called planets, are the largest objects
in the solar system.
• Terrestrial planets have solid, rocky crusts; these
four inner planets are Mercury, Venus, Earth, and
• Gas giant planets are more gaseous and less
dense then the other planets; these four outer
planets are Jupiter, Saturn, Uranus, and Neptune.
Planet Earth
Getting to Know Earth
• The atmosphere, hydrosphere, and lithosphere form
the biosphere, the part of Earth that supports life
for all people, animals, and plants.
• Atmosphere is a thin layer of gases that surround
Earth and contains the air we breathe.
• Hydrosphere includes the liquid and frozen surface
water, groundwater, and water vapor in and around
oceans, lakes, and rivers on Earth.
• Lithosphere is the land or surface areas on Earth,
including the continents, islands, and ocean basins.
Forces of Change
Earth’s Structure
• For millions of years, the surface of the Earth has
been moving.
• The Earth is composed of three layers—the core at
Earth’s center, the mantle layer of dense rock on
the outer core, and the crust forming Earth’s
• Many scientists believe Earth was once a single land
mass called Pangaea, but then continental drift
slowly spread the continents apart.
• Plate tectonics describes the activities of
continental drift and magma flow; referring to the
physical processes that create and shape continents,
islands, oceans, and mountain ranges.
Forces of Change
Internal Forces of Change
• Mountains are formed when Earth’s giant continental
and oceanic plates collide.
• Moving plates sometimes cause Earth’s surface to
buckle forming folds; in other cases the moving
plates form cracks called faults.
• Violent movements of Earth’s crust along fault lines
are called earthquakes, which dramatically change the
surface of the land and the floor of the ocean.
• Volcanoes are mountains formed by lava or magma
that breaks Earth’s surface.
Forces of Change
External Forces of Change
• Wind and water break down the Earth’s surface
through weathering and erosion.
Physical weathering happens when large masses of
rock are broken down into smaller pieces.
Glaciers are large bodies of ice that move across the
Earth’s surface, changing the landscape as they flow.
Soil building takes thousands of years of weathering,
erosion, and biological activity and is influenced by
five factors; climate, topography, geology, biology,
and time.
Earth’s Water
The Water Cycle
• Almost all of the hydrosphere is saltwater found in
oceans, seas, and some lakes.
• The amount of water on Earth never changes, but it
is constantly moving through the processes of
evaporation, condensation, and precipitation.
• Evaporation is when the sun’s energy causes water
to change into vapor or gas.
• Condensation is an excess of water vapor that
changes into liquid water after warm air cools.
• Precipitation is the release of moisture through
rain, snow, or sleet.
Earth’s Water
Bodies of Salt Water
• Seventy percent of the Earth’s surface is water,
primarily salt water.
• Salt water cannot be used for drinking, farming, or
• Due to a growing population and the need for more
freshwater, some countries are focusing on the
desalination process, which removes the salt from
• Desalination is expensive and is also controversial;
critics believe the process has negative environmental
and economic impacts.
Earth’s Water
Bodies of Freshwater
More than two-thirds of the world’s scarce freshwater
is frozen in glaciers.
Less than one-third of a percent of freshwater is found
in lakes, rivers, and streams and their tributaries.
Aquifers and groundwater are important sources of
freshwater found underground within the Earth.