E&U L5

Lesson 6

Sea Floor Spreading

Learning Outcomes

You will be successful if you can:

• Know that sea-floor spreading causes the continents to move

• Describe how magnetic field reversals led to the acceptance of continental drift.

• Explain how the movement of tectonic plates leads to unpredictable earthquakes. .

Compare and contrast

• How is the model like "real-life" - i.e. the seafloor

• How is the model different from what really happens under the sea?

• What simplifications have we made?

Evidence for sea floor spreadingSince the Earth was formed the north and south poles have periodically “________ ____”. When tectonic plates move apart and _____ fills the gap the iron particles in the magma orientate themselves in line with the Earth’s ________ field. This means that the rock formed on the sea floor contains a “magnetic __________” of the changing field:

These magnetic patterns can be used to prove that sea floor spreading does happen, and at a rate of about 2 to 10 cm per _____.

Words: impression, magma, swapped over, magnetic, year

Fact

Seafloor drilling in 1969 found that sediments further away from oceanic ridges are thicker

1) How do you think this is linked to the age of the rock

a) close to the ridgeb) far away from the ridge?2) How is this evidence for sea floor

spreading?

How far does the Atlantic spread in a lifetime? (100 years)

How far has it spread in all of human history?

(10 000 years)

How far has it moved in 100 million years?

Review

Crust Mantle Core

Heat Low density Tectonic plates

Africa S America Rock types

Oceanic Plate Fossils High Density

Subduction Earthquakes

Magnetic reversal pattern

Continental plate

Radioactive Decay