Interior of the Earth

Question 1

How do we know about the structure of Earth’s interior?

Answer 1

We study how earthquake waves pass through Earth (seismology)

Question 2

Order of Earth’s interior layers

Answer 2

Crust, mantle, outer core, and inner core

Question 3

Coldest interior layer of Earth

Answer 3

Crust

Question 4

Hottest interior layer of Earth

Answer 4

Inner core

Question 5

Thickest interior layer of Earth

Answer 5

Mantle

Question 6

Thinnest interior layer of Earth

Answer 6

Crust

Question 7

Densest interior layer of Earth

Answer 7

Inner core

Question 8

Which interior layers of the Earth are solid?

Answer 8

The crust, the inner core, and the mantle (behaves as a plastic)

Question 9

Which interior layers of the Earth are liquid?

Answer 9

Outer core

Question 10

What layer is under the most pressure? Why?

Answer 10

The inner core, because there is so much rock pushing on it from above

Question 11

What is the core composed of?

Answer 11

The core is composed of a nickel-iron alloy

Question 12

Why is the outer core liquid while the hotter inner core is frozen?

Answer 12

• The inner core is under a lot of pressure, and pressure raises the melting point
• In addition when a substance melts it expands, and due to the pressure the core can’t expand

Question 13

When was the layered structure of Earth established?

Answer 13

• 4.6 b years ago: planet so hot - entire thing liquid, no core yet- homogeneous: liquid rock and liquid iron throughout
• As it cools off, pools of liquid iron (nickel, etc.), liquid rock and Liquid iron do not mix (immiscible), liquid iron is denser, goes to the center of the Earth (<50 million years old), shell of solid rock on surface
• Inner core became solid about a billion years ago
• Crystal of solid iron/nickel that grew

Question 14

What causes the Earth’s magnetic field?

Answer 14

The flow of liquid iron in the outer core generates electric currents, which produce magnetic fields

Question 15

Equation for the percentage of the volume of the core of a planet

Answer 15

Volume of a sphere: 4πr3 / 3

Percentage: Volume of core / Volume of planet

Question 16

What are the most important sources of Earth’s internal heat?

Answer 16

1. Radioactivity
2. Leftover heat from Earth’s formation
3. Pressure

Question 17

Is the Earth cooling off or warming up?

Answer 17

The Earth is slowly cooling off

Question 18

What is the difference between the asthenosphere and the lithosphere in terms of temperature, pressure, and rigidity?

Answer 18

• The lithosphere consists of the crust and uppermost mantle and is rigid
• It is colder than the asthenosphere and is less dense
• The asthenosphere consists of the rest of the mantle and behaves as a plastic
• It is warmer than the lithosphere and denser

Question 19

What is a plate?

Answer 19

• The outermost shell of the Earth, and consists of the crust and the rigid uppermost part of the mantle
• They are transported across the surface of the Earth as they ride on the top of large mantle convection cells
• 12 large plates + 12 smaller plates

Question 20

What are the differences between oceanic and continental plates?

Answer 20

• Oceanic plates are denser and thinner than continental plates
• They also tend to be younger, because they subduct at convergent boundaries

Question 21

What were the main pieces of evidence Wegener used to construct his theory on continental drift?

Answer 21

1) The continents seemed to fit together like a jigsaw puzzle
2) Fossils of prehistoric species were found on separate continents that would fit together if his theory was correct
3) Matching rock types were found on separate continents that would also fit together
4) Ancient glacial sediments found in places too warm for glaciers to form

Question 22

Why was Wegener’s theory not accepted for several decades?

Answer 22

• He thought that the continents plowed through the rock of the ocean floor - disproved by geologic evidence
• Continental drift was not accepted until Harry Hess had a hypothesis of seafloor spreading

Question 23

Divergent boundary

Answer 23

• Ex: mid-Atlantic ridge
• Where two plates are pulled apart from each other
• Shallow earthquakes can occur (100 km)
• Volcanic activity occurs due to decompression melting
• Oceanic ridges are created, with a rift valley in the center

Question 24

Convergent boundary

Answer 24

• Where two plates move toward each other
• Shallow, intermediate, and deep earthquakes can occur
• Volcanic activity occurs - melting of the mantle
• Structures: trench, subduction zone, arc

Question 25

Transform boundary (ex)

Answer 25

- Where two plates slide past each other - There can be shallow earthquakes (0-100 km) - No volcanic activity - Most occur in the middle of the oceans and connect segments of oceanic ridges (divergent margins) - Ex: San Andreas fault (California)

Question 26

Ocean-ocean convergent plate boundary

Answer 26

- Where two oceanic plates meet and one is subducted beneath the other - The older plate (which is colder and denser) subducts beneath the younger one - denser - Ex: Philippines, Aleutian Islands, Lesser Antilles

Question 27

Ocean-continent convergent plate boundary (ex)

Answer 27

- Where an oceanic plate meets a continental plate and the denser oceanic plate sinks beneath the less dense continental plate - Ex: Andes Mountains, Cascade Mountains

Question 28

Continent-continent convergent plate boundary (ex)

Answer 28

- Where two continental plates collide with each other - Neither plate can sink beneath the other (can't be subjected) because they both have low densities - Instead, the crust folds and enormous mountain chains are produced - Ex: Himalayas, Alps, Appalachians

Question 29

Where are the majority of earthquakes and volcanoes located?

Answer 29

At plate boundaries

Question 30

In what hemisphere are the majority of earthquakes and volcanoes located? Why?

Answer 30

- In the northern hemisphere, there are more plate boundaries, which is where volcanoes form - They especially form at convergent boundaries, which the northern hemisphere has a lot of

Question 31

Alfred Wegener

Answer 31

A german meteorologist and climatologist who made the first hypothesis of the continental drift theory

Question 32

Arc

Answer 32

A line of volcanoes that forms parallel to the trench in a convergent boundary

Question 33

Asthenosphere

Answer 33

Consists of most of the mantle and behaves as a plastic

Question 34

Lithosphere

Answer 34

- Consists of the crust and uppermost mantle and is rigid | - It is relatively cool and not dense

Question 35

Oceanic Ridge

Answer 35

- Created at divergent margins - Long chains of mountains within ocean basins - In a few locations, so much volcanic activity has taken place that it forms volcanic islands (Iceland) - Rift Valley usually exists at center of ridge - represents the boundary between the two diverging plates

Question 36

Pangea

Answer 36

The supercontinent that formed 300 million years ago that broke apart 250 million years ago

Question 37

Panthalassa

Answer 37

The single large ocean that covered Earth’s surface during the time of the supercontinent Pangea

Question 38

Radioactivity

Answer 38

The emission of ionizing radiation or particles caused by the spontaneous disintegration of atomic nuclei

Question 39

Rigid

Answer 39

- If an object is bent, it will go back to its original form if released - If it is bent too far, it will snap

Question 40

Subduction

Answer 40

When an oceanic plate begins to sink into the mantle

Question 41

Trench

Answer 41

- A long depression where the oceanic plate begins to sink into the mantle - Pacific Ocean lined with trenches (Mariana Trench)

Question 42

Volcanic activity at divergent margins

Answer 42

- Mantle melts due to decompression melting - Resulting mags ascends, erupts, and solidifies to create basalt (volcanic rock) - Basalt represents new oceanic crust - New crust forms - older crust pushed farther from ridge on either side - Result: youngest crust in the ocean basins is at mid-ocean ridges, oldest crust farthest from ridges - disappears into subduction zones close to continent

Question 43

Convergent margin earthquakes

Answer 43

- Shallow, intermediate, and deep earthquakes can occur - Occur within upper part of lithosphere as it descends into the mantle - Below a depth of 700 km, the sinking lithosphere moves as a plastic and there are no earthquakes

Question 44

Convergent margin volcanic activity (ex)

Answer 44

- Volcanic activity occurs because as the oceanic lithosphere sinks into the mantle, it heats up, forcing water to leave it and enter the mantle above the plate - This water lowers the melting point of the mantle - Product of this melting of the mantle: a line of volcanoes (an “arc”) over the subducted lithosphere - Examples: Mt. St. Helens, Mt. Pinatubo, Mt. Jujiyama, Krakatoa - Volcanoes often more explosive + dangerous - contain more gases such as water vapor and carbon dioxide

Question 45

Plate tectonics

Answer 45

- The interaction of plates - Vast majority of earthquakes and volcanoes occur at the boundary between these plates - Explains why seafloor spreading and continental drift occur

Question 46

Magnetic evidence of seafloor spreading

Answer 46

-As lava cools, the iron-bearing minerals (mainly magnetite) align with the prevailing magnetic fields -Evidence for geometric reversals first came from lava flows of various ages -If you know how old the rocks are, you can determine when thee reversals were Magnetometer. - device that measures strength of magnetic fields (over rocks with normal polarity = high magnetic strength, reverse polarity = low – cancel out) Symmetrical pattern on either side of the ridge -If you know when the reversal a specific point happened and how far away it is from the ridge, you can figure out how rapidly -Key piece of evidence