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PLATE TECTONICS
LAYERS OF THE EARTH
LITHOSPHERE vs ASTHENSOPHERE
• LITHOSPHERE - crust together with a hard upper part of the mantle (PLATES, Crust under
continents, crust under ocean
• ASTHENOSPHERE – (Below Lithosphere) So much pressure and heat the rocks can flow like
a liquid. Allows Lithosphere to “float” on top of it.
• HOW TO REMEMBER: L.A. Lithosphere on outside, Asthenosphere on in the inside. L.A.
CRUST
OUTER MOST LAYER
THINNEST LAYER
LAND, OCEAN FLOOR, PLATES
CONTINENTAL CRUST
OCEANIC CRUST
Under the Land
Under the ocean
THICK CRUST (20-40
miles thick)
LOW DENSITY
LIGHT COLOR
GRANITE
THIN CRUST (3 miles
thick)
HIGH DENSITY
DARK COLOR
BASALT
LAYERS
We used Seismic Data (from earth quakes etc) to
develop our model for what the interior of the earth is
made of.
The deepest we have ever drilled doesn’t even reach the mantle
MANTLE
OUTER CORE
INNER CORE
TAFFY LIKE (not solid, not
liquid)
Outer Mantle & Crust
form Lithosphere
Inner Mantle
forms Asthenosphere
Thick Liquid Metal
Solid
Magnetic Field
Dense Metal
8100 Degrees F
Iron and Nickle
1800 Miles Thick
9000 Degrees F
LAYERS and CHARACTERISTICS
Layers formed using differentiation:
More dense (heavier) materials went
to the center (CORE)
Less dense (lighter) materials went
to the crust (PLATES, ROCKS)
***Differences in DENSITY separate
the earth’s layers
AS DEPTH INCREASES (closer to center of earth)
As depth INCREASES, Temperature INCREASES
As depth INCREASES, Pressure INCREASES
As depth INCREASES, Density INCREASES
TEMPERATURE INCREASES
PRESSURE INCREASES
DENSITY INCREASES
RAIO ACTIVE DECAY – Earth’s internal heat source
Earth has been losing heat since it formed,
billions of years ago. But it’s producing
almost as much heat as it’s losing. The
process by which Earth makes heat is called
radioactive decay. It involves the
disintegration of natural radioactive
elements inside Earth – like uranium, for
example. Uranium is a special kind of
element because when it decays, heat is
produced. It’s this heat that keeps Earth from
cooling off completely.
Continental Drift Theory
• 1910 Alfred Wegener
• Hypothesis: all the
continents had once
been joined together in a
single landmass
PANGEA!
• Evidence: Land “fit”
together like puzzle,
Fossils, BUT…. He
couldn’t explain how the
continents actually
moved apart. So they
rejected him!
SEA-FLOOR SPREADING (helped explain continental drift)
• Occurs at mid-ocean ridges
• Ocean floors move like
treads on a bulldozer or tank
• Lava rises from the mantle
through the ridge. Lava then
spreads out, pushing older
rock to both sides of the
ridge.
• Magma flows upward
because it is LESS DENSE
then the surrounding rock.
As distance from the mid-ocean ridge increases – The Age of the crust
increases (further away the older… closer to the ridge the younger)
• Lava rises,
then cools at
the ridge.
New lava
rises and
pushes the
existing
cooled lava
away from
the Ridge.
This Repeats.
Why don’t the oceans continue to get wider and wider if the sea floor is
spreading?
Deep-ocean
trenches form
where oceanic crust
bends downwards.
SUBDUCTION:
process where
ocean floor sinks
beneath a deepocean trench and
back into the
mantle.
CONVECTION drives
sea floor spreading.
THEORY OF PLATE TECTONICS
• Lithosphere is broken up into separate sections called PLATES.
• Plates carry the continents or part of the ocean floor.
• Theory of Plate Tectonics states that pieces of the earth’s lithosphere are in
constant, slow motion, DRIVEN BY CONVECTION CURRENTS in the mantle.
• Plates of Lithosphere float on top of the asthenosphere.
• Convection currents rise in the asthenosphere and spread out
beneath the lithosphere. Causes plates to move. If one plate moves,
it makes another move.
• As plates move, they collide, pull apart, or grind past each
other…..producing Mountains, volcanoes, and Deep Sea Trenches.
PLATES (*Pacific plate and North American Plate
EVIDENCE OF PLATE TECTONIC MOVEMENT
1. Matching up rock layers over wide distances
2. Matching up fossils, and plants over wide
distances
3. Noticing forces that happen today and knowing
they happened in the past. (Subduction,
Convection, Faulting) (Uniformitarianism)
DIVERGENT BOUNDARY
Two plates move apart (divide)
Mid Ocean Ridge is Divergent Boundary
If divergent boundary is on land, Rift Valley forms.
Rift Valley Kenya (divergent)
CONVERGENT BOUNDARY
Two plates move towards each other (Converge)
Himalaya Mountains are Convergent boundary
Himalayan Mountains (cont – cont convergent)
TRANSFORM BOUNDARY
Two plates slip past each other moving in opposite directions
SAN ANDREAS FAULT is transform boundary (Pacific plate & North Amer. Plate
San Andreas Fault ( Transform boundary)