Evidence for Plate Tectonics

How many magnetic reversals have been mapped in the ocean floors over the world?

171

Where are most earthquakes in the world located?

Along plate boundaries.

How does magnetic striping work?

As molten rocks cool, magnetic materials line up with the Earth's magnetism and then remain that way. When the Earth's magnetism changes, the lining up of the minerals in the new magma will also change.

Why do most coral reefs only occur in the upper levels of the ocean?

Because the coral polyps need special conditions of oxygen, food and light that are only accessible in the upper parts of the ocean.

What is the age of the oldest continent rocks vs the age of the oldest ocean floor rocks?

Continent rocks are 4000 million years old, and ocean floor rocks are 200 million years old. Ocean floor rocks are *younger* than continent rocks. This is because the ocean floor is *continually* being *recycled*. Old material is *pushed back* into the upper mantle. New material is *added* to mid ocean ridges. The further away the ocean floor is to the mid ocean ridge, the older it is.

What's another name for mid-ocean ridges?

Divergent zones.

What is another way the water depth could change?

During an ice age, the sea level can fall a great distance as water in the form of ice collects on the land. This has resulted in approximately 130 metres below the present (I have no idea what that means).

True or false- All areas along divergent zones are moving are moving at the same rate.

False

Drilling on coral islands has revealed that coral occurs to depths greater than 1200 metres. How can this be explained?

It can be explained by a gradually decreasing depth of water which may be a result of the movement of ocean crust away from the mid-ocean ridge.

What are the five main pieces of evidence for the Theory of Plate Tectonics?

Magnetic striping, Age of the ocean's crust rocks, Coral islands, The position of ocean trenches and the locations of earthquakes and volcanoes.

What indicates that the materials line up with the Earth's magnetism?

Mirror-image patterns along mid-ocean ridges.

What are coral polyps?

Reef-building animals

Alterations in the Earth's magnetism are called what?

Reversals.

What are ocean trenches?

Very deep areas of the ocean.

How do volcanic island arcs occur?

When old ocean rocks are forced down beneath a continental plate, they cause magma to rise, creating a volcano.