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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
sun.
• 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
Mars.
• 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
surface.
• 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
manufacturing.
• Due to a growing population and the need for more
freshwater, some countries are focusing on the
desalination process, which removes the salt from
seawater.
• 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.