Chapter 1: The Earth in Context Slide Set 3

Question 1

The Earth produces a ___________ that shields the planet from _____________ .

Answer 1

Magnetic field

solar wind

Question 2

How was the oxygen in our atmosphere mainly generated?

A.By volcanic activity during the first billion years of Earth’s history.
B.By life and photosynthesis.
C.By the greenhouse gas emissions during industrial revolution.
D.By the oxygen-producing process of moisture in the atmosphere condensing and raining out to form the oceans.

Answer 2

A

Question 3

What is Earth made of?

Answer 3

Silicate (SiO4) Minerals

• Most common mineral in the Earth
• A compound of silicon and oxygen

Question 4

Rank the silicon content of Earth in decreasing order

Answer 4

• Felsic (or silicic)
• Intermediate
• Mafic
• Ultramafic

Density increases with decreasing silicon content. Consequently, felsic rocks are less dense than mafic rocks

Question 5

What is the crust composed of?

Answer 5

• 98.5% of the crust is composed of just eight elements.
• Oxygen is the most abundant element in the crust.
• Crust is high silicate, low density.

Question 6

What are the elements that comprise the mass of the entire Earth?

Answer 6

• The elements that comprise the mass of the entire Earth are dominated by Iron (core) and Oxygen.

Question 7

How do we know the Earth has layers?

Answer 7

• The first key to understanding Earth’s interior: density.
• When scientists first determined Earth’s mass they realized:
  **Average density of Earth&raquo_space; average density of
  surface rocks.
  **The Earth is round, and rotating
  **Deduced that metal must be concentrated in Earth’s
  center.
• These ideas led to a layered model: Earth is like an egg.
  **Thin, light crust (eggshell)
  **Thicker, more dense mantle (eggwhite)
  **Innermost, very dense core (yolk)

Question 8

How do we know what the Earth’s layers are like?

Answer 8

• When rocks in the subsurface break and slip along a fault, they generate shock waves that travel outward to form an earthquake.

Question 9

Approximately how much of the Earth’s surface is covered by ocean? / What is the average depth of the ocean?

A. 70% / 3.7 km
B. 30% / 0.9 km
C. 60 % / 6.1 km
D. 75%/0.37km

Answer 9

A

Question 10

Zero elevation on a topographical map represents the average elevation of the whole solid surface of the Earth

True/False –> EXPLAIN WHY?

Answer 10

False

Average elevation, % of surface area of Earth
land: +0.88 km, ~30%
Ocean: -3.7 km, ~70%

From this we could make an estimate of the average elevation of the whole solid surface as:
0.880.3 + 3.70.7 = -2.3 km

Question 11

What happens to the pressure and the temperature as the depth increases?

Answer 11

Pressure (P) –> The weight of overlying rock increases with depth.

Temperature (T) –> Heat is generated in Earth’s interior. T increases with depth.

Question 12

What is geothermal gradient? How does it vary in terms of depth?

Answer 12

It refers to the rate of change in temperature with depth

• The rate of T changes with depth.
• The geothermal gradient varies.
  * * ~ 20-30°C per km in crust
  * * < 10°C per km at greater depths
  * * Earth’s center may reach 4,700°C!

Question 13

What is Moho?

Answer 13

Andrija Mohorovicic (1857-1936) discovered that	the velocity of earthquake waves suddenly increased at	depth of tens	of km beneath the	Earth’s surface and he	suggested that this increase	was	caused by an	abrupt	change in the	properties of rock. Later studies showed	that	this change can be found most everywhere around our planet, though	it occurs at different depths in different	
locations. Specifically, the area of	change is deeper	beneath continents than beneath	oceans. This change	is known	as Moho

Question 14

What are the layers of the crust? What are their properties (rock composition etc.) and what makes them different?

Answer 14

Oceanic crust –> underlies seafloor (1-10 km thick). The top of the oceanic crust is composed of a blanket, generally less than 1 km thick, of sediment – clay and tiny shells that settled out of the sea like snow. Beneath this blanket, the oceanic crust consists of a layer of basalt and below that a layer of gabbro.

Continental crust –> (35-40 km thick) but thickness varies significantly. It contains a great variety of rock types, ranging from mafic to felsic in composition. On avg., upper continental crust has felsic (granite-like) to
intermediate compostion – so continental crust overall is less than the oceanic crust.

Question 15

What is the mantle?

Answer 15

Mantle forms 2,885 km thick later surrounding the core. In terms of volume it is the largest part of the Earth.
- Consists entirely of an ultramafic (dark and dense) rock
called peridotite (the most abundant rock in our planet)
- The seismic wave velocities change at a depth of
410km and again at a depth of 660km in the mantle.

Question 16

What are the layers of the mantle? What are their properties (rock composition etc.) and what makes them different?

Answer 16

1. Upper mantle (depth = 660 km) –> the lower part of the upper mantle is called the transition zone – in this zone, seismic wave velocities increase in series of steps, due to abrupt changes in the structure of minerals making up mantle rock.
2. Lower mantle (depth = 660 – 2900 km) –> Almost all of the mantle is solid rock-melt – which occurs in films or bubbles between grains, accounts for just a few percent of its volume, and generally occurs at depth of 100 to 200 km only beneath the ocean floor. Even though its mostly solid, mantle rock below depth of 100 to 150 km is too hot that it is soft enough to flow (15 cm a year).

Question 17

What is the core?

Answer 17

An iron-rich sphere with a radius of 3,471 km

Question 18

What are the layers of the core? What are their properties?

Answer 18

Seismic waves segregate two radically different parts.

• The outer core is liquid;
• The inner core solid (greater pressures keep it solid).

1. Outer core –> (2900 - 5155 km deep) Iron alloy is liquid because the temperature of the iron core is so high that even the great pressure squeezing the region cannot keep atoms locked into a solid form. The liquid iron alloy’s rapid flow generates Earth’s magnetic field
2. Inner core –> (5155–6371 km deep, radius – 1200 km) is a solid iron alloy that may reach temperature of over 4700 degrees Celsius. Even though it is hotter than the outer core, the inner core’s alloy remains solid because it is deeper and is subjected to greater pressure, which keeps atoms locked together tightly in solid crystals.

Question 19

What is lithosphere and how does it differ from other layers?

Answer 19

The outermost 100–150 km of Earth

• Behaves rigidly, as a non-flowing material
• Contains the crust and part of the upper mantle
• This is the material that makes up tectonic plates.

Question 20

How are the lithosphere and the crust related?

Answer 20

Lithosphere and crust are not the same - the crust is only the top layer of the lithosphere

Question 21

What is asthenosphere and how does it differ from other layers?

Answer 21

Upper mantle below the lithosphere

• Shallow under oceanic lithosphere; deeper under continental
• Flows as a soft solid.

Question 22

How many types of lithosphere are there? What are their properties (composition, density, etc.) and their differences?

Answer 22

Continental Lithosphere:

• ~150-250 km thick
• Felsic to intermediate crustal rocks
  
  • • 25–70 km thick.
  • • Lighter (less dense).
  • • More buoyant—floats higher.

Oceanic Lithosphere:

• ~100 km thick
• Mafic crust: basalt & gabbro
  
  • • <10 km thick.
  • • Heavier (more dense).
  • • Less buoyant—sinks lower towards center of Earth.

Question 23

Is the temperature the same everywhere inside the Earth?

A. Yes. The temperature of the Earth is constant
throughout.
B. No. The temperature increases with increasing depth.
C. No. The temperature decreases with increasing depth.
D. No. The temperature increases, then decreases,
then increases, then decreases.

Answer 23

C

Question 24

Do seismic waves travel at the same velocity throughout the Earth? Why?
A. No. The velocity changes with depth at a constant rate.
B. Yes. The velocity is the same at all depths.
C. No. The velocity changes with depth, and at certain
depths the change is abrupt.
D. Bogus question. Seismic waves cannot travel through
the Earth.

Answer 24

C

Question 25

What are the two most common components of Earth’s atmosphere?
A.  Nitrogen and oxygen
B.  Oxygen and carbon dioxide
C.  Nitrogen and argon
D.  Argon and oxygen
E.  Carbon dioxide and water vapor

Answer 25

A