Chp 7: Earth

Question 1

density of Earth

Answer 1

-Densest major body in the solar system (5.5 g/cm3)

Question 2

2. What makes Earth unique among the terrestrial planets?

Answer 2

Of the terrestrial planets:

• Earth’s magnetic field is uniquely strong;
• Mercury has a much weaker magnetic field,
• Venus has none
• Mars’ field is extremely weak.

Question 3

3. Explain the role of Accretion in the formation of the Earth

Answer 3

• accretion (growth by accumulation of smaller bodies, dust and gas) of smaller objects. The first large object would have attracted others by simple gravity
• as the object grew larger, it attracted more and more material to it faster and faster.
• it became a protoplanet, and then a planet.

Question 4

What is the iron catastrophe?

Answer 4

• hot liquid iron from the upper layer would begin to pool and sink under its own great weight.
• iron sinking to the planet’s core produced upheaval of the planet, releasing more energy and caused the whole planet to melt.

Question 5

What is the most common element in the Earth?

Answer 5

Oxygen

Question 6

How did differentiation form different zones in the Earth?

Answer 6

• during the period when all Earth was molten, there was a general zonation of elements from heaviest at the core to lightest at the top; of course, the zonation was not complete, so there still are many heavy elements at surface.
• This process of chemical zonation from core to surface is called differentiation.
• the zones of differentiation are called inner core, outer core, mantle and crust, with oceans and atmosphere sitting on top . All of this was probably complete by 4.4 billion years ago.

Question 7

Name the zones of the Earth (be able to label a simple diagram). How do the zones differ from each other? Which is the largest zone?

Answer 7

• Lithosphere (uppermost mantle and crust)
• Asthenosphere (crust)
• Mesosphere (mantle) (largest zone) (Solid)
• Outer core (liquid)
• Inner core (solid)
• differ physically and chemically
• from surface to core, both pressure and temperature, and density increase.

Question 8

How do pressure, temperature and density change as you move from the crust towards the core?

Answer 8

from surface to core:

both pressure and temperature, and density increase.

Question 9

Why does Earth have a magnetic field? What is a dynamo?

Answer 9

• The magnetic field of Earth is caused by currents of electricity that flow in the molten core.
• dynamo is simply a mechanical device that converts physical energy to electrical energy. Anywhere that electrical energy flows, there’s a magnetic field surrounding it.

Question 10

What is the evidence that supported the hypothesis of continental drift?

Answer 10

• the distribution of ancient fossils, rocks, and mountain ranges (Leonardo da Vinci/Charles Darwin)
• the locations of ancient climatic zones
• the fit of the continents (Alfred Wegener, North and South America were joined with Europe and Africa as one enormous continent he called Pangaea)

Question 11

What are the 3 types of plate margins? What happens at each kind of margin?

Answer 11

-Divergent margins (spreading centres)
-Convergent margins (the edge of one plate (whichever is more dense) sinks beneath the edge of the second plate, subduction)
-Transform Fault Margins (two plates slide past each
other, strike-slip faults.)

Question 12

What mechanism drives plate tectonics (a.k.a. continental drift)?

Answer 12

• heat transfer.
• Heat is produced within the Earth through radioactive decay.
• That heat production provides a tremendous driving force to move material around, in the process of convection.

Question 13

What is a mantle plume and how does it form?

Answer 13

• we defined the mesosphere as a zone that acts as a stiff plastic
• that ‘stiff plastic’ isn’t stable right next to the liquid metal core: the fierce heat of the adjacent core produces large pockets of hot
• therefore less dense, material that starts to rise (like a hot balloon) through the more stable mesosphere above it.
• Once started, it just continues – giving rise to a ‘plume’ of hot material that may rise right to the base of the lithosphere

Question 14

What is “relative age dating”? Give an example of how you can tell the order in which rocks were formed based on their relative position.

Answer 14

• Geologists can unravel the sequence of rock formations in the field by looking at their relative relationships.
• For example, when observing a sequence of undisturbed horizontal sedimentary rocks that the layers at the bottom of the sequence are older than those at the top.

Question 15

Describe (generally) how we can use radioactive elements to determine absolute ages of rocks.

Answer 15

what we need to determine the age of most rocks is:

• The rate of radioactive decay (we call that rate the half-life)
• The amount of the isotope that is in the process of breaking down (we call it the parent)
• The amount of the isotope produced by the breakdown (we call it the daughter).

Question 16

How old is the Earth? How old is the surface of the Earth? How old are the ocean floors?

Answer 16

• Earth is 4.5 billion years old
• oldest surviving rock is about 4 billion years old
• ocean is about 250 million years old

Question 17

Describe how the Earth’s atmosphere, hydrosphere and biosphere are interconnected (e.g. how do they affect each other).

Answer 17

these subsystems work together to influence the climate, trigger geological processes, and affect life all over the Earth.

Question 18

Why does Earth’s atmosphere differ from that on Mars? Venus?

Answer 18

• the fact that Earth is covered by vast quantities of liquid water and is teeming with plant life that uses photosynthesis
• The oceans provide an enormous heat reservoir that stabilizes Earth’s climate and keeps the planet’s surface temperature at optimal levels for the life forms inhabiting it.

Question 19

Where did the Earth’s water come from?

Answer 19

• comet and many asteroids that pummelled Earth contained small quantities of water.
• when the surface of Earth had cooled sufficiently, water vapour in the atmosphere started to condense and rain began.
• When it started raining, a layer of liquid water was born (our oceans, lakes and rivers).
• The hydrosphere is the combined mass of water found on, under, and above the surface of a planet.

Question 20

Explain two ways that biology has affected the composition of the atmosphere – how are these changes beneficial to life?

Answer 20

• First, through the process of photosynthesis (by which plants combine CO2 and H2O to form organic matter and O2), the biosphere added oxygen to the atmosphere.
• Second, by removal of carbon from the atmosphere to form organic matter and limestone, the biosphere lowered the CO2 content; as a result, the temperature declined.

Question 21

How did prokaryotes that lived in anaerobic ancient oceans avoid the toxic effects of the oxygen they produced during photosynthesis? What evidence do we have?

Answer 21

• Unlike today’s oceans, they were enriched in dissolved iron (introduced by the abundant submarine volcanism of the day).
• if you leave metal iron sitting in the open air, it will rapidly rust (i.e., it will oxidize) by absorbing free oxygen from the air.

Question 22

How do we finally start to accumulate oxygen in the atmosphere and what were the effects on biology/evolution?

Answer 22

eukaryotes:
- used oxygen for respiration,
- Grew rapidly in very large colonies,
- Were truly photosynthetic (so produced large amounts of oxygen),
- contributed a great amount of oxygen to the atmosphere, and rapidly changed the biosphere of Earth.

Question 23

How is CO2 removed from the atmosphere? How does this affect Earth’s temperature?

Answer 23

As land forms rose above sea level

• weathering (by acidic rain) and erosion proceeded. A multitude of elements ended up in solution in seawater as a result.
• calcium (Ca) was a major component carried by the slightly acidic ‘fresh’ water of rivers to the sea.
• Once in the seas, Ca may chemically combine with carbon dioxide and form grains of calcite (CaCO3) which precipitate and form limestone, or may be consumed, again with carbon dioxide, to form skeletons/shells for marine organisms.
• CO2 is removed from the ocean water/atmosphere ‘budget’, the temperature declined.

Question 24

Main elements in the Earth’s atmosphere.

Answer 24

78% nitrogen, 21% oxygen, and the other 1% contains traces of many elements and compounds, including argon, carbon dioxide, water, krypton and xenon.

Question 25

How was the core formed? What are the layers of the core?

Answer 25

• The primary result, as far as distribution of elements was concerned, was to remove much – but certainly not all – of the iron from Earth’s outer layers to form a liquid core of nearly 100% metal (mostly iron, plus some other heavy metals that accompanied iron).
• As Earth continued to grow, the confining pressure on the innermost core became so great that it was transformed from a liquid to a solid – giving Earth a hot central core of solid metal inside an outer core of liquid metal.

Question 26

The study of magnetic properties of rocks is called:

Answer 26

paleomagnetism

Question 27

Method of detecting seismic waves

Answer 27

seismic tomography

Question 28

The big block of time just before 545 million years ago is called:

Answer 28

the Proterozoic (meaning development of life).

-Most life during that time was soft-bodied, and constructed of simple cells; there were no significant hard parts to be preserved as fossils.

Question 29

all of time from the Cambrian Period until present day is called:

Answer 29

-The Phanerozoic, when there has been abundant, complex life.
-The Phanerozoic is divided into 3 main periods:
Paleozoic (early life), Mesozoic (middle life) and Cenozoic (recent life).

Question 30

The most common radioactive elements used:

Answer 30

uranium and thorium

Question 31

An _______ environment is one that contains little to no oxygen.

Answer 31

anaerobic

Question 32

The Earth’s core is (2 facts)

Answer 32

• Hotter in its centre than the surface of Sun

- Larger than the Moon

Question 33

Earth’s initial (primary) atmosphere

Answer 33

Hydrogen and Helium

Question 34

Earth’s secondary atmosphere

Answer 34

Mainly carbon dioxide

Question 35

Earth’s modern day (tertiary) atmosphere

Answer 35

Mostly Nitrogen and Oxygen