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