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Earth Sciences > 3. Earth's Composition and Structure > Flashcards

3. Earth's Composition and Structure Flashcards

1
Q

Rosetta mission

A
  • mission to land robot Philae on comet 67P that was 317 million miles away from Earth
  • Goal: measure Deutrium/ Hydrogen ratio of water ice to find origin of water on Earth
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2
Q

Deuterium

A

an isotope of Hydrogen. Has an extra neutron, so twice as heavy as H.

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3
Q

Earth’s Crust

A
  • where most of Earth’s chemical diversity is >4000 diff minerals
  • continental and oceanic crust
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4
Q

What is continental crust?

A
  • thicker than oceanic
  • older than oceanic– rocks preserved at cratons
  • thicker at roots of mountains
  • 20-90 km thick
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5
Q

What is oceanic crust?

A
  • thinner than continental crust (20-90 km thick). This is 5-10 thick
  • created at spreading ridges and subducted into mantle at convergent plate boundaries
  • process takes 200 million yrs– so it’s that old
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6
Q

Where is the oceanic crust created and subducted?

A
  • oceanic crust created at spreading ridges
  • subducted into mantle convergent plate boundaries
    200 ma process
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7
Q

What is the earth’s 3 layers?

A

crust, silicate mantle, core

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8
Q

What are the parts of the core and what is it made out of?

A
  • liquid outer core and solid inner core

- Mostly Fe or Fe- Ni alloy (iron and iron nickel mixture)

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9
Q

What is the moho?

A
  • a compositional boundary that separates the crust and mantle
  • rocks at crust are different than rocks at mantle
  • moho is deeper in continental crust (20-90km) than ocean crust (5-10 km)
  • seismic waves bounce off of this
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10
Q

What is the lithosphere?

A

The part of the crust and upper mantle that’s rigid. Sits on top of asthenosphere.

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11
Q

What is the asthenosphere?

A

The part of the upper mantle that’s ductile. Sits below lithsosphere.

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12
Q

What is Rheology?

A

the mechanical properties of materials.

- ex- lithosphere is rigid, asthenosphere is ductile

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13
Q

What is project mohole?

A

The first attempt to drill into the mantle. only got 180 m

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14
Q

Have we ever drilled into the mantle?

A

No

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15
Q

What is the Kola Superdeep borehole?

A

The deepest hole on Earth
12km
Russia
Failed because temperatures were too hot and broke drillbit

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16
Q

What is the sedimentary wedge and what does that have to do with the carbon cycle?

A
  • off the Pacific coast
  • buildup of terrestrial and marine carbon
  • Will it
    a) be heated and pressurized to form kerogen- rock carbon, which will be subducted into mantle under North America
    b) broken down and re-enter surface as C02
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17
Q

What is a xenolith?

A
  • term that refers to foreign rocks
  • volcanoes spew these out
  • a green xenolith is a peridotite
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18
Q

What is a peridotite?

A
  • a green xenolith
  • brought up by basaltic magma (volcanoes) and kimberlites (that also bring up diamonds)
  • made of orthopyroxene and olivine, which has Mg/ Si ratio of 2 and 1. Because these are close to 1.5 (ratio of chondrite), we know that peridotite makes up mantle
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19
Q

What 2 rocks make up the mantle? And what does the mantle have to be able to produce?

A
  • peridotite and Ilerzolite

- have to be able to produce basalt

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20
Q

What is PREM (Preliminary Reference Earth Model)?

A

Graph that gives us information on P-wave velocity, S-wave velocity, density in depth
- avoids info about rock chemistry, composition, temperature

21
Q

Does the Earth’s water come form comets? Why or why not?

A
  • Nope
  • the Detrium/ Hydrogen ratio on comets is 3x that of earth
  • it should match
22
Q

Where does Earth’s water come from?

A
  • We don’t really know!
  • Not from comets
  • We think it derives from building blocks of Earth- chondritic meteorites
  • There are some questions we have though: hydrogen is volatile and should have burned up. Maybe it survived/ stable in magma ocean. We don’t know how it performs in deep-mantle conditions.
23
Q

How deep is the core?

A

4000 miles under us

24
Q

What did large-scale melting result?

A

Core, Silicate mantle, Crust

25
Q

Which are more common? Chondrites or undifferentiated bodies?

A

Chondrites- 86%

26
Q

What two rocks do we think make up the upper mantle and why?

A
  • we think olivine and orthopyroxene make up the upper mantle because their Mg/ Si ratio is close to chondrites. 2 and 1
  • Chondrites is 1.5
  • Chondrites are building blocks of solar system and have to have similar composition to Earth
27
Q

What three types of differentiated meteorites are there?

A
  1. Iron meteorites - come from the core (5%). Made of Iron
  2. Stony-Iron/ Pallesite– core mantle (1%) . Made of metal and silicate (olivine)
  3. Stony/ achrondite- crust/mantle (8%). Made of silicate.
28
Q

Order the differentiated and undifferentiated meteorites in order of how rare they are.

A 
Common
Chondrites 86%
Stony/ achrondite 8%
Iron (5%) 
Stony-iron/ Pallesite 1%
Rare
29
Q

Is the earth a perfect sphere?

A

Nope

It’s spinning and it’s elastic

30
Q

Are the earth’s oldest rocks on the planet?

A

Nope

Plate tectonics erased them

31
Q

How have the drilling programs helped us?

A

They’ve helped us develop theories around plate tectonics and continental drift

32
Q

Have we drilled into the mantle yet? How far have we gone?

A

Nope we have not
Kola superdeep borehole
In russia, 12 km

33
Q

How are crustal rocks brought up to us?

A

By tectonics
- We know that quartz have been at the crust because they’ve been own X km depth because at Y km depth and pressure, albite turns into jadeite.

34
Q

Why is peridotite not the only thing the mantle is made of?

A
  • when melted, peridotite doesn’t produce basalt.

- peridotite is residue of whatever the mantle is actually made of.

35
Q

What is basalt made of?

A

plagioclase feldspar and clinopyroxene

36
Q

What did early models of the mantle look like?

A

plum pudding model: peridotite with chunks of eglotite

37
Q

What is the mantle made of ?

A

garnet-peridotite aka Ilerzolite

38
Q

What 3 types of seismic waves are there?

A
  1. P- Wave
    - primary, fastest, compressional like sound waves
    - body wave
  2. S-Wave
    - secondary, shear waves, slower than P-waves
    - body wave
  3. Surface Wave
    - cause shaking
39
Q

What are body waves?

A
  • A type of seismic wave that propagates through the interior of the earth, but not liquid.
  • P and S waves
  • Speed influenced by temperature, melting, mineralogy, composition
  • Bounce off the core
40
Q

What 3 things does a seismogram measure and what are they?

A
  • amplitude- strength of earthquake
  • time- helps us locate them. Need 3 stations.
  • frequency- give us info about internal structure of earth
41
Q

Is the mantle completely solid?

A
  • No
  • the mantle is solid all the way to the core-mantle boundary, but there’s a small amount of melt (10-15%) that’s along the spreading ridges, ocean islands(possible plumes of melt), back-arc settings (behind subducted slabs)
42
Q

What elements are missing from Peridotite to make the mantle ?

A

Ca and Al needed to make basalt

43
Q

What is the sedimentary wedge and what does it have to do with the carbon cycle?

A
  • a buildup of sedimentary waste of the coast of the Pacific Northwest
  • Scientists wonder:
    a) will it be broken down and return to the earth as CO2?
    b) will it be heated and pressurized to form kerogen (rock carbon) and be subducted into the mantle under North America
44
Q

What is kerogen?

A
  • rock carbon

- waste (like the sedimentary wedge) can be heated and pressurized to form this

45
Q

What is a xenolith?

A
  • a foreign rock
  • volcanoes bring them up
  • green xenoliths are peridotite
  • by looking at the composition, we can tell what the mantle is made of
46
Q

What is a peridotite?

A
  • green xenolith that basaltic magmas (volcanoes) bring up
  • Made of olvidine and orthopyroxene. We know because they have a Mg/ Si ratio of 2 and 1, and chondites have 1.5 ratio, that this is a good representation of what the mantle is made of
  • in mantle
47
Q

What is PREM- Preliminary Reference Earth Model?

A
  • Gives us information on P-wave velocity, S-wave velocity, density in terms of depth
  • limited in information. Doesn’t give regional, chemical, compositional, temperature info
48
Q

Does Earth’s water come from comets? Why or why not?

A
  • Nope.
  • The Deutrium and Hydrogen ratio on comets is 3x that on Earth.
  • They should match if comets brought water.
49
Q

Where do we think water comes from?

A
  • we think water was part of original building blocks of earth– chrondritic meteorites (we knew they were full of hydrogen adn water) ;sdkjfsdfsdfosdpf’asdfasdgk;jsdgdafmnb dvb ovo huhkw FA

Earth Sciences (15 decks)

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