Plate tectonics

Question 1

Creation of the earth

Answer 1

1) At the center of the earth is the CORE, which is split into an inner and outer core:
>The inner core is a solid ball containing lots of iron and nickel.
>The outer core is semi-molten and also contains lots of iron and nickel.

2) Around the core is the mantle, which is mainly made of silicate rocks:
>The part of the mantle nearest the core is quite rigid.
>The layer above this, called the asthenosphere, is semi-molten (it can flow)
> Th very top part of the mantle is rigid.

3) The outer layer of the Earth is called the CRUST.

4) The rigid top part of the mantle and the crust together are called the LITHOSPHERE.

5) There are two types of crust- CONTINENTAL and OCEANIC:
-the continental crust is thicker and less dense ( 30-70 km thick)
- Oceanic crust is thinner and denser (6-10km)

Question 2

The Earth’s surface is separated into plate margins

Answer 2

1) The lithosphere is divided into lots of slabs called tectonic plates, which move in relation to each other.

2) The place where plates meet are called plate boundaries and plate margins.

3) The idea that the Earth’s lithosphere is made up of plates that move is called the theory of plate tectonics.

Question 3

What are convection currents? (tectonic plate movement)

Answer 3

1) The Earth’s mantle is the hottest close to the core, so lower parts of the asthenosphere heat up, become less dense, and slowly rise.

2) As they move toward the top of the asthenosphere they cool down, become denser, and slowly sink.

3) These circular movements of semi-molten rock are called convection currents.

4) They create drag on the base of the plate tectonics, causing them to move.

Question 4

What is slab pull? (tectonic plate movement)

Answer 4

1) At destructive plate margins, the denser crust is forced under the less dense crust.

2) The sinking of the plate edge pulls the rest of the plate towards the boundary.

Question 5

What is ridge push? (tectonic plate movement)

Answer 5

1) At constructive plate margins, magma rises to the surface and forms a new crust, which is very hot. It heats the surrounding rocks, which expand and rise above the surface of the surrounding crust, forming a slope.

2) The new crust cools and becomes denser. Gravity causes the denser rock to move downslope, away from the plate margin.

3) This puts pressure on the tectonic plates, causing them to move apart.

4) Ridge push is also known as gravitational sliding.

Question 6

When does sea floor spreading occur?

Answer 6

1) As tectonic plates diverge (move apart), magma rises up to fill the gap created, then cools to form a new crust.

2) Over time, the new crust is dragged apart, and even more new crust forms between it.

3) When this happens at a plate margin the sea floor gets wider.

4) This process is called seafloor spreading.

5) It creates structures called mid-ocean ridges- ridges of higher terrain on either side of the margin.

6) A similar process of spreading occurs at land margins where the plates are moving apart.