Sea Floor Spreading and Plate Tectonics

Chapter 1.4 and 1.5

Ch. 1.4 Sea-Floor Spreading

Mid-Ocean Ridge• longest chain of mountains in

the world

• all below the ocean

• Scientists use SONAR

to map them

SONAR -a device that records echoes of sound wavesHistory of Ocean Drilling

2. Sea-floor spreading?

• At the mid-ocean ridge, molten material rises from the mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge.

Earth's Volcanic History

3. Scientists found Evidence

Molten Material found

• as pillow-shaped rocks

• hardened quickly

3. Scientists found

Evidence

Magnetic patterns or stripes found in

• Ocean floor rock

• Reversals of Earth’s magnetic field

3.3. Scientists found

Evidence

Drilling core samples

• age of rock samples

• The farther away from the mid-ocean ridge, the older the rocks

Drilling for Cores Samples

4. Subduction at Deep-Ocean Trenches

• Subduction:

a process where the ocean floorsinks beneath a deep-ocean trenchand back into the mantle…over tens of millionsof years.Sketch this picture

5. Subduction at Earth’s Oceans

Drilling in the Arctic Ocean

Ch. 1.5 Theory of Plate Tectonics

Plate Motion• Pieces of Earth’s lithosphere are in constant

slow motion• Driven by convection currents in mantle• Theory of Plate Tectonics explains the

§ Formation§ Movement§ Subduction of Earth’s plates

Plate Boundaries

• Plate boundaries are- where edges of lithosphere meet

• Faults are- breaks in the crust, where rocks that slip past each other form at plate boundaries

3 Types of Plate BoundariesTransform boundaries

• Where 2 plates

slip past each

other

Plate boundariesDivergent boundaries

• Where 2 plates move apart

• A rift (deep) valley forms

2. Plate boundaries Convergent

• Where 2 plates come together or collide

The plate density determines which plate goes under-subduction

Where continental crusts collide-it forms mountains

Plate boundaries

Continent’s Slow Dance

• 225 million years ago, plates joined together- Pangaea

• 180-200 mya Continents split apart, narrow seas become oceans

• 135 mya Continents began to drift apart• 65 mya India a separate continent,

Australia connected to Antarctica

• Today continents look like puzzle pieces that once were together

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