Download Earth Structures Day two plates

Earth Structures
Day 2: Plate Boundaries and Movement
Goal:
▪ I will be able to differentiate between
the types of plate boundaries
▪ I will be able to recognize what a
fossil is and how it relates to plate
boundaries
Plate Tectonics
▪ Many years ago… in 1915 a scientist by the
name of Alfred Wegener suggested that the
continents were moving very slowly!
▪ His theory became known as the
continental drift.
SHOW ME THE EVIDENCE!!!
▪ Wegener said that he knew his theory to be true
because of fossils that were found and because
of different rock formations.
▪ What is a fossil you ask?
▪ A fossil is a physical remain or trace of a
plant or animal that lived long ago.
▪ Usually found in sedimentary rock
But what about……
▪ He was unable to explain how
the continents moved through
the solid crust of the ocean
floor.
▪ He also could not explain the
forces that move the
continents.
Thus his theory was
REGECTED!
New discoveries every day!
1950’s
The lithosphere is not
one solid shell of rock
▪ Molten rock was rising from
the mantle onto the ocean
basins. As the rock cooled it
hardened and was being added
to the earth’s crust!
Because of this discovery:
▪ Scientists now believe that the
crust is broken up into giant
slabs of rock called plates.
▪ These plates seem to “float” on
top of the mantle, much like
giant ships float on a sea of
molten rock.
Plate Tectonics
The idea that giant plates of
rock are moving slowly across
the Earth’s surface
The plates are moving relatively slow:
the average speed is about 10 cm or 4 inches
a year
Kinds of plates
Oceanic Plates
Continental
Plates
Consist almost
entirely of dense
ocean floor
material
Made up of lighter
continental rock
“riding” on top of
denser rock.
Plate Interaction
▪Plates interact at
their edges or
plate
boundaries.
Converging Boundaries
Two plates move toward each
other.
Eventually the plates will
collide.
One plate may move under
the other one in the process
called subduction.
When will subduction occur?
Subduction usually occurs
when a continental and
oceanic plate converge
The dense rock of the oceanic
plate slides under the lighter
rock of the continental plate.
Diverging
▪ Two plates move away or diverge from each other.
▪ Molten rock will rise up between the two rocks forming
new crust.
▪ This usually happens in the middle of the ocean floor,
so it is also called sea- floor spreading.
Sliding Boundaries
▪Plates may also slide past each
other in opposite directions.
Moving Plates
▪ Whether converging, diverging or sliding, Earth’s plates never stop moving
and changing!
▪ New rock is added to the Earth’s crust in some places, Old rock is “lost” to
the mantle in other places.
▪ Moving, separating and merging of the continents has been occurring for
billions of years. Some of these changes are constructive and others are
destructive.
Where is your Evidence Mr. Science Man?
▪ Scientists claim that the plates have been moving for about 2 billion years
▪ Their evidence comes from the rocks at the Earth’s surface.
▪ Layers of sedimentary rocks provide clues to changes that were taking
place at the time the layers were forming.
What can these rock layers prove?
The layers show the mineral content of the
rocks and how the sediment was
deposited.
The layers may also contain fossils.
How can studying fossils help prove the plates
are moving?
▪ Fossils of similar species were buried on opposite sides of
the ocean along the edges of different continents.
▪ Scientists have stated that this must have happened
during a time that the continents were joined, like
PANGEA!
▪ Over time the continents separated, thus the fossils are
on different continents.
Fossils
▪ Some fossils seem to also be very far from where they were
deposited.
▪ Fossils of tropical plants and animals have been found in
polar regions.
▪ Fossils of salt water fish have been found far from oceans
▪ Scientists believe that the moving of the plates carried
these fossils to their current location.