Transcript Plate Tectonics

Plate Tectonics
8th Grade Science
Earth’s Composition
Tectonic Plates
-Pieces of lithosphere that move around on
asthenosphere
-Earth’s lithosphere is broken into about 19 pieces
-Fit like pieces of a giant jigsaw puzzle
-Some plates contain only continental crust, some
have only oceanic crust, some have both
Map of Tectonic Plates
Tectonic Plate Close-Up
Mapping Earth’s Interior
-Seismic waves –
earthquake waves
-Travel through different
densities & materials at
different speeds
Alfred Wegener
-Proposed Theory of
Continental Drift
-idea of once giant
landmass (Pangaea)
that broke & drifted to
present locations.
Evidence for Pangaea
-Continents seem to “fit” together.
-Fossils of same plant & animal species
found on opposite sides of oceans.
-Same types of rocks & layers found on
coasts on opposite sides of oceans.
-Evidence of same climactic conditions on
several continents.
Fossil Evidence
Pangaea & its Break Up
-245 mya
-existed while some
of the earliest
dinosaurs
roamed.
-Continents “broke”
over time
-Drifted to current
locations
Sea-Floor Spreading
-Tectonic plates move away from each other
-New oceanic lithosphere forms as magma
rises up & solidifies.
-Older crust gets pushed further away.
-Happens at Mid-Ocean Ridges.
Sea-Floor Spreading
Evidence for Sea-Floor Spreading
-Records of magnetic reversal in ocean floor.
-when Earth’s poles change, polarity of poles
change.
-Molten rock at ridges contain grains of
magnetic material (iron) – act like little
compasses.
-Creates bands of grains pointing in opposite
directions – bands are light/dark.
Magnetic Reversal
Plate Boundaries
-Places where tectonic plates meet.
-3 types: convergent, divergent,
transform
Convergent Boundaries
-2 plates collide or converge
-3 types of convergent boundaries:
1. continental/continental – mountains form
2. continental/oceanic – subduction zones –
volcanoes form
3. oceanic/oceanic – subduction – volcanoes
-Subduction – sliding of one plate under another
Divergent Boundaries
-2 plates separate or diverge
-As they separate, magma rises to fill the
gap
-Forms mid-ocean ridges and rift valleys
Transform Boundaries
-2 plates slide past each other horizontally
-Plates grind & jerk as they slide
-Produces earthquakes
Why do the Plates move?
-CONVECTION CURRENTS in the MANTLE!!!
-hot magma from deep inside Earth rises.
-cools as it rises.
-sinks back into deep Earth as it cools.
Convection
Pangaea Ultima?
-Due to plate motion, the continents will
continue to drift……
-One leading theory now is that they will all
reunite into a giant landmass they call
Pangaea Ultima.
-Let’s take a look…..
Pangaea Ultima