EARTH’S INTERNAL
FORCES
HOW EARTH IS SHAPED
• Internal and external forces both shape the
Earth’s surface.
• The Earth’s internal and external structure,
including the tectonic plates, is responsible
for the creation of continents, mountain
ranges, volcanoes, etc.
DEFINING INTERNAL & EXTERNAL
FORCES
• Internal processes take place within/inside
the earth’s surface. For example: plate
tectonics, volcanic formations, earthquakes,
etc.
• External processes take place outside the
earth’s surface. For example: floods,
avalanches, tornadoes, etc.
EARTH’S STRUCTURE
• Many scientists believe that most of
the landmasses forming our presentday continents were once part of
one gigantic supercontinent called
Pangaea.
•Due to continental drift, they slowly
separated.
•Due to plate tectonics, the physical
features of the planet are constantly
changing.
WEGENER’S THEORY
OF CONTINENTAL DRIFT
• http://www.youtub
e.com/watch?v=QL
7LX5-ytOg
EARTH’S LAYERS
• The Earth is composed of three main layers:
– The core
– Inner and outer core
– The mantle
– The crust
– The crust and upper mantle
– http://www.youtube.com/watch?v=bgnn096PfWQ
EXPLANATION OF EARTH’S PLATES
• The earth's crust is not a solid shell; it is broken
up into huge, thick plates that drift atop the
soft, underlying mantle.
• The plates drift all over the globe; they move
both horizontally (sideways) and vertically (up
and down).
• Over long periods of time, the plates also
change in size as their margins are added to,
are crushed together, or pushed back into the
earth's mantle.
THE EARTH AS A CRACKED EGG
• Think of the earth’s crust as a cracked or fractured
egg that is composed of many parts that form the
entire shell.
THE EARTH’S PLATES
PLATE TECTONICS
• Plate tectonics is the movement of earth’s
plates.
• Plate tectonics is responsible for the folding,
lifting, bending, and breaking parts of the
Earth’s surface.
• As the plates converge or diverge they
create landforms.
• http://www.youtube.com/watch?v=1HwPR_4mP4
SUBDUCTION
– When two plates converge the heavier goes
under the lighter.
– The process of two plates converging is called
subduction.
– A trench is the deep valley that forms as a result
of subduction
– During subduction the submerged plate grinds
against the plate above it and heat is
generated often causing a row of volcanoes.
– When these volcanoes raise to the surface we
call them island chains.
FOLDS & FAULTS
– Moving plates that become compressed or
smashed are called folds.
– Moving plates that slide or move apart from each
other are called faults.
– A fault line is where two plates meet. Also called a
plate boundary.
– Earthquakes occur typically along fault lines.
– Tension builds up along fault lines as the plates grind against
one another. This grinding causes sudden vibrations that
we call earthquakes.
HOW MOUNTAINS ARE FORMED
http://www.history.com/topics/himalayas/videos mountain-building
• http://www.youtube.com/watch?v=goszsQl0Bc0
REVIEW
• What is an internal force and provide three
examples?
• What is plate tectonics and what are three reasons
that it is important?
• What are the three layers of earth and which is
made of iron?
• In your own words define subduction and then
draw an image to represent what the process looks
like.
EXTERNAL FORCES
• Weathering is when rocks break away or decay
over time.
• The Earth is changed by two basic kinds of
weathering:
– Physical weathering – occurs when large masses
of rock are physically broken down into smaller
pieces.
– Chemical weathering- changes the chemical
makeup of rocks. For example, rain water that
contains carbon dioxide from the air easily
dissolves certain rocks, such as limestone.
TYPES OF EROSION
– Erosion is the movement of surface material from
one location to another by water, wind and ice.
– Wind erosion involves the movement of dust, sand,
and soil from one place to another.
– Plants help protect the land from wind erosion;
however, in dry places where people have cut
down trees and plants, winds pick up large amounts
of soil and blow it away.
OTHER TYPES OF EROSION
– Glacial Erosion: as glaciers move, they may destroy
forests, carve out valleys, alter courses of rivers, and
wear down mountaintops, changing the
landscape.
– Water erosion: it begins when spring water and
rainwater flow downhill in streams, cutting into the
land, and wearing away the soil and rock.