Plate Tectonics

Chapter 1

How thick is the inner core?

1,200km thick

How hot is the inner core?

6,000°C

In what state is the inner core?

Solid, due to intense pressure

What is the composition of the inner core?

Mostly iron, with small amounts of nickel and sulfur

How thick is the outer core?

2,200km thick

How hot is the outer core?

4,000°C

In what state is the outer core?

Molten

What is the composition of the outer core?

Iron and nickel

How thick is the mantle?

2,900km thick

What percentage of the earths volume does the mantle make up?

75%

In what state is the lower mantle?

Molten magma (liquid rock)

What are endogenic forces?

Forces from within the Earth that cause the crust to move vertically or horizontally

What are mainly responsible for endogenic forces?

Convection currents

How thick is the asthenosphere?

100-200km thick

In what state is the asthenosphere?

Semi-molten

What sits on top of the asthenosphere?

The solid upper mantle

What two layers of the Earth form the lithosphere?

The solid upper mantle and the crust

How thick is the lithosphere?

50-200km thick

What is the name of the boundary that separates the solid upper mantle from the crust?

Moho line

What name is given to the broken sections of the crust?

Plates

What are the names of the seven major plates?

North American plate, Pacific plate, Nazca plate, Eurasian plate, South American plate, African plate, Indo-Australian plate

What are the names of the seven, less important plates?

Juan de Fuca plate, Cocos plate, Caribbean plate, Scotia plate, Antarctic plate, Arabian plate, Philippine plate

What are the two types of crust?

Continental crust and oceanic crust

What is the average thickness of continental crust?

45km thick

What kind of rock forms continental crust?

Light rock (e.g. granite)

What does SIAL stand for?

Silica and alumina (continental crust)

What is the average thickness of oceanic crust?

8km thick

What kind of rock forms oceanic crust?

Heavy rock (e.g. basalt)

What does SIMA stand for?

Silica and magnesium (oceanic crust)

What layer of the Earth do the plates slide on top of?

Asthenosphere

What are the four main parts of the theory of plate tectonics?

Continental drift

Thermal convection currents

Seafloor spreading

Subduction

Who proposed the theory of continental drift?

Alfred Wegener

What does continental drift propose?

It proposes that all of Earth’s landmasses were once joined together as one supercontinent, which began to break apart

What was the name of the original supercontinent?

Pangaea

How long ago did Pangaea start to break apart?

200 million years ago

What were the names of the two supercontinents Pangaea first broke into?

Gondwanaland and Laurasia

What evidence supports continental drift?

Continental fit

Matching plant fossils

Matching animal fossils

Matching rock folds

Matching glacial deposits

What is continental fit?

The coastlines of the continents got together like a jigsaw puzzle (e.g. the east coast of South America and the west coast of Africa)

What was the plant that matching fossils were found for?

Glossopteris

Why does the discovery of Glossopteris across continents support continental drift?

Plants usually grow in specific climate conditions, so this suggests they must have been joined in the past

What ancient reptile’s fossils was found to support continental drift?

Mesosaurus

Where were the Mesosaurus fossils found?

South America and Africa

Why does the discovery of matching Mesosaurus fossils support continental drift?

The Mesosaurus was a freshwater reptile, meaning it couldn’t survive in the Atlantic Ocean, so it couldn’t have swam to another continent. The distance between the continents is also too far for it to have swam

Where are identical rock folds found?

Along the Eastern coast of North America (Appalachian Mountains) and the North-Western coasts of Europe (Ireland, Scotland, Scandinavia)

How long ago were the matching mountains formed and what are they made of?

Formed 400 million years ago and are made of granite

Why do matching glacial deposits support continental drift?

Glacial deposits are found places such as central Africa, along the equator, which is far too hot to support glaciers currently. This suggests that the continents must have been in a different part of the world at some point

Who first suggested that thermal convection currents cause the plates to move?

Arthur Holmes

How are thermal convection currents created?

Magma deep in the Earth’s mantle is heated by the core. As the magma is heated, it rises towards the crust. As the magma reaches the upper mantle, it begins to cool and becomes semi-molten. The cooking magma moves sideways and sinks back down again. As the magma moves sideways beneath the lithosphere, it causes friction, causing the plates to move apart, collide or slide past each other

What allowed a survey of the floor of the Atlantic Ocean to be carried out?

New technology after WWII

Who discovered how mid-ocean ridges form?

Harry Hess

The separation of what plates form the Mid-Atlantic Ridge?

The North American and Eurasian plates

How long is the Mid-Atlantic Ridge?

16,000km long

How do mid-ocean ridges form?

Thermal convection currents pull two plates apart. As they separate, lava pours out from the gap between the plates. This lava cools quickly and forms new seafloor. As more lava pours out and solidifies, rock builds up and forms a mid-ocean ridge. This makes the ocean wider

What two methods can be used to prove seafloor spreading?

Age of seafloor and ocean sediment

How does the age of the seafloor prove seafloor spreading?

Rock closest to the ridge is much younger than rock closer to a continent (e.g. seafloor closer to the Mid-Atlantic Ridge is 10 million years old, and seafloor near North America and Europe is 180 million years old)

How does ocean sediment prove seafloor spreading?

Seafloors are gradually covered in sediment over time. Seafloor close to continents has much thicker layers of sediment than seafloor close to mid-ocean ridges, suggesting that the seafloor closer to continents is older

Who conducted further studies of the ocean floor and discovered deep ocean trenches?

Frederick Vine and Drummond Matthews

Why doesn’t the Earth grow in circumference if new seafloor is being made?

As new seafloor is created at mid-ocean ridges, older seafloor is destroyed at subduction zones

What is subduction?

Subduction is when the edge of an oceanic plate bends down into the mantle, where it melts at a depth of 100km.

Do continental plates or oceanic plates move faster and why?

Oceanic plates move faster due to slab pull

What is slab pull?

When an oceanic plate sinks into the mantle, it’s surrounded by liquid. Before it melts, it sinks further down and drags more of the plate into the mantle.