Dynamic Earth Lecture 2

Question 1

What is sea floor spreading?

Answer 1

When the seafloor spreads apart along both sides of a mid-ocean ridge as new crust is added.
This makes the seafloor move like a conveyor belt, carrying the continents along with it.

Question 2

What is the evidence for sea floor spreading?

Answer 2

Molten material, magnetic stripes, and drilling samples.

Question 3

Describe the evidence from molten material.

Answer 3

Scientists found pillow-shaped rocks near ocean ridges.

Question 4

Describe the evidence of magnetic stripes.

Answer 4

Scientists found rocks on both sides of mid-ocean ridges with magnetic polarity and reversed magnetic polarity. The Earth’s magnetic field matched the rocks.

Question 5

Describe the evidence of drilling samples.

Answer 5

Newer rock is found near mid-ocean ridges and older rock is found near trenches.

Question 6

What is subduction?

Answer 6

At a deep ocean trench, the ocean floor bends downwards and sinks back into the mantle.

Question 7

Compare new ocean floor vs. old ocean floor.

Answer 7

Newer ocean floor is hotter and lighter.

Older ocean floor is cooler and denser.

Question 8

What kind of ocean floor does gravity pull beneath the trench?

Answer 8

The older, denser ocean floor.