Plate Tectonics

Question 1

Until the mid 1900s, what did scientists believe about the continents?

Answer 1

They believed the continents had been in the same location since the Earth was formed.

Question 2

What led Alfred Wegener to come up with the Continental Drift Theory?

Answer 2

He noticed some of the continents looked like they fit together like a puzzle. He also collected rock, climate and fossil information from around the world to find evidence for his theory.

Question 3

What is the Continental Drift Theory?

Answer 3

That the continents were one single land mass 200 million years ago and then drifted apart.

Question 4

What was the super continent called and what does it stand for?

Answer 4

Pangaea.

Pan means “All”
Gaea means “World”

Question 5

Why did scientists reject the Continental Drift Theory at first?

Answer 5

Because Alfred Wegener couldn’t explain how the contients could move and scientists could not imagine what forces could be large enough to make a continent move.

Question 6

What discoveries supported the Continental Drift Theory?

Answer 6

Discoveries about the ocean floor and what the inside of the earth is made of supported the idea that continents move.

Question 7

What is the modern theory of how continents move called? (NOT Continental Drift Theory)

Answer 7

Plate Tectonics Theory

Question 8

How do scientists study what the interior of the Earth is made of?

Answer 8

Scientists infer the earth’s structure by studying energy waves that travel through the interior during earthquakes. The speed of the waves is affected by the type of material they pass through.

Question 9

Starting at the surface of the Earth and moving inward, name all the parts of the Earth and, briefly, what they are made of.

Answer 9

Crust: Mostly granite.
Upper Mantle: Solid at the top, like soft taffy below.
Lower Mantle: Made of denser, more solid material
Outer Core: Liquid
Inner Core: Very hot, more than 5000 degrees Celsius. Solid because dense and upper pressure.

Question 10

What creates movement under the crust of the Earth?

Answer 10

The temperature differences within the mantle. This is called a convection current.

Question 11

What two things does the ocean floor consist of?

Answer 11

Mid-ocean ridges: Mountain ridges along the ocean floor as high as 3km
and
Trenches: Deep valleys in the ocean floor, thousands of kilometres long (deepest: Marianas Trench, 11km deep)

Question 12

The ocean floor near mid-ocean ridges is [ ] than ocean floor farther away from ridges.

Answer 12

Younger

Question 13

What is sea floor spreading?

Answer 13

The process of magma rising to surface at mid-ocean ridges to form new ocean crust. Magma cools and hardens into rock and pushes older rock away from the ridge. The process is repeated over millions of years and results in new oceanic crust.

Question 14

The layer of sediment gets [ ] as you move further away from ridges.

Answer 14

Thicker.

Question 15

What are tectonic plates?

Answer 15

Huge slabs of rock that float very slowly on a layer of fluid-like rock in the Earth’s mantle. There are 12 major tectonic plates and many smaller ones.

Question 16

What does the Plate Tectonics Theory explain?

Answer 16

It is a unifying theory that explains:

• how and why continents move
• how and why sea floor spreading occurs
• how, why and where earthquakes, volcanoes and the formation of mountains occurs

Question 17

Explain what the “slab pull” process is.

Answer 17

Slab pull: Pulling of a tectonic plate due to gravity and subduction. As leading edge of a plate sinks, it pulls the rest of the plate with it as it goes under.

Question 18

What are three types of plate boundaries and briefly explain them?

Answer 18

Divergent plate boundary: Where tectonic plates move apart and create new oceanic crust. Occurs where the sea floor spreads along a mid-ocean ridge. Can also occur in the middle of continents (continental rifting).

Convergent plate boundary: When an ocean plate goes under a continental plate, the denser crust eventually goes below the less-dense crust in a process called subduction. Volcanoes and mountains form at these boundaries.

Transform plate boundary: Where two tectonic plates slide past each other horizontally. Earthquakes are common at these boundaries.

Question 19

What is the lithosphere?

Answer 19

The Earth’s outer layer of solid rock composed of crust and part of the upper mantle.

Question 20

In mantle convection, what happens to material of different temperatures?

Answer 20

Warmer, less dense material rises.
Cooler, denser material sinks.

This creates very large convection currents in the mantle. As the mantle material moves, it drags the tectonic plates above with it.

Question 21

Where do earthquakes occur and why?

Answer 21

Almost all earthquakes occur along plate boundaries.

Movement in the earth’s crust can squeeze, stretch or twist the rock, which applies pressure to the rock. Stored energy in the rock is released as an earthquake.

Question 22

What is a fault?

Answer 22

A fault is a large break in the rock where movement happens, causing earthquakes.

Question 23

Where do earthquakes start?

Answer 23

An earthquake starts at the focus, a point usually several kilometres below the earth’s surface where the break in rock first happens.

Question 24

What is the epicentre of an earthquake?

Answer 24

The point on the Earth’s surface above where an earthquake starts (the focus).

Question 25

What are seismic waves?

Answer 25

Vibrations caused by the release of energy during an earthquake.

Question 26

What are the three types of seismic waves and briefly describe them.

Answer 26

P (Primary) Waves: Move the fastest. Are the first ones detected in an earthquake. Cause rock particles to move forward and backward. Can travel through liquids and solids.

S (Secondary) Waves: Move slower than P Waves. Cause rock particles to move up and down. Can only travel through solids.

L (Surface) Waves: Slowest of the three waves. Are on the surface and often cause the greatest damage. Cause rock particles to move up and down AND side to side. Can travel along the surface of the earth and NOT through the Earth’s interior.

Question 27

How are earthquakes measured?

Answer 27

With a seismograph, an instrument that measures and records seismic waves (ground vibrations).

Question 28

What is the Richter scale?

Answer 28

A scale for reporting the magnitude (strength) of an earthquake. Based on the size of the largest seismic waves that are formed. A higher number means a bigger/stronger earthquake.

Question 29

How much bigger is a magnitude-8 earthquake than a magnitude-7 earthquake on the Richter scale? Than a magnitude-6 earthquake?

Answer 29

Each number on the Richter scale represents a 10 fold difference.

Therefore, a magnitude-8 earthquake is 10 times larger than a magnitude-7 earthquake and 100 times larger than a magnitude-6 earthquake.