Download The Lithosphere - Westmount High School

THE LITHOSPHERE
Living on Shaky Ground
The Lithosphere is the outer shell of the Earth including the crust and the
upper mantle. It is composed of brittle rock.
The lithosphere is broken into the tectonic plates. The plates or chunks of
crust, drift about on the magma in the mantle below.
They move only a few centimeters a year.
DEFINITION
The lithosphere is a rigid structure that comprises
the Earth’s crust and part of the upper mantle.
- Mountains, volcanoes, caves, hills, plains
and
more are located in or on the lithosphere.
- The lithosphere is constantly changing its
appearance because of climate changes and
human activity.
- It ranges between 70 and 150 km in depth.
CONTINENTAL DRIFT
Alfred Wegener developed the idea of continental drift.
Continental drift: The continental drift theory is the theory that once all
the continents were joined in a super-continent, which scientists call Pangaea.
He made many observations before he concluded that the continents
were all once joined together.
- Fossils of animals that could not swim or fly were found
on the west coast of Africa and on the South America.
- The shapes of both Africa and South America fit
together like a jigsaw puzzle.
- Certain mountain chains had similar rock composition (he
thought that they all once belonged to one large mountain chain)
PANGEA & PANTHALASSA
Pangea is the name given to the supercontinent that existed long
ago.
Panthalassa is the name given to the ocean that Pangea was in
(Pangea resembled an island in one big ocean).
PLATE TECTONICS
PLATE TECTONICS
Wilson, a Canadian geophysicist, developed the idea of plate tectonics.
Once scientists had discovered that the upper mantle, the asthenosphere, was
composed of partially melted rock, Wilson realized that the continents could
move because they were “floating” on a mud-like substance.
Plate tectonics: earth’s crust is divided into large rigid plates that move.
As the plated move on the upper mantle, they cause, among others,
earthquakes, tsunamis, the formation of mountains and volcanoes.
CONVECTION: HOW PLATES
MOVE
Plates move because of convection currents in magma, beneath the plates.
As the magma is heated when it is close to the core, it rises. It moves
horizontally because new molten rock is pushing it. As it moves horizontally, it
takes the plate on its surface with it. The magma will cool down and fall back
to the core where it is heated again and rises – the cycle continues.
HOW DO THEY MOVE?
Plates can move:
a) Apart (divergent boundary)
b) Toward each other (convergent boundary/subduction or collision)
c) Against each other (transform boundary)
PRESSURE BUILDS UP
Compression of a tectonic plate
Continent to continent collision
VOLCANOES
A volcano is a rupture or a break in a planets crust where hot magma, ash, and
gases are released.
Volcanoes are usually found where plates are diverging (going apart) or
converging (coming together).
Before an eruption there are many small earthquakes because moving magma
pushes the ground out of it’s way.
CONVERGENT BOUNDARIES
Oceanic-continental convergence = SUBDUCTION
When an oceanic plate pushes into and subducts under a continental plate, the
overriding continental plate is lifted up and a mountain range is created.
CONVERGENT BOUNDARIES
Oceanic-oceanic convergence
When two oceanic plates converge one is usually subducted under the other
and in the process a deep oceanic trench is formed.
OROGENESIS: MOUNTAINS
Mountains are either formed by the subduction of an oceanic plate under a
continental plate or by the collision of two continental plates.
EATHQUAKES
When two plates move sideways against each other (at a transform plate
boundary), there is a tremendous amount of friction which makes the
movement jerky. The plates slip, then stick as the friction and pressure build
up to incredible levels. When the pressure is released suddenly, and the plates
suddenly jerk apart, this is an earthquake.
TSUNAMI
A tsunami is series of huge ocean waves caused by a rapid, large-scale
disturbance of the sea water. Tsunamis are caused by earthquakes the seafloor.
In deep water, tsunami waves are less than a meter high, but they can travel at
speeds exceeding 800 kilometers per hour and can easily cross an entire ocean
basin.
HUMANS & THE LITHOSPHERE
How do humans affect the lithosphere?
-humans put carbon into the atmosphere
-logging has killed trees and stopped them from using the carbon
-land uses such as agriculture, livestock grazing, and draining swamps
move carbon from the soil to the atmosphere.