Exam 3

Question 1

Describe the Ordovician extinction:

• Common theories for cause
• Life forms wiped out
• Characteristics of climate
• Characteristics of atmosphere
• How long ago, what % lost

Answer 1

• Caused by two pulses:
  
  • First pulse due glaciation with associated CO₂ levels dropping, likely due to silicate sequestering or plant colonization.
  • Second pulse due to regression of glaciation.
• Life forms affected: invertebrates living in shallow seas; nautiloids, corals, graptolites, to name a few.
  
  • Severely impacted trilobites (90+ %)
• Climate a warm greenhouse in beginning/majority.
  
  • Extensive glaciation occured at end of period.
• Carbon levels were high during most part of period, and dropped during glaciation event, and rose again when glaciers receded.
• 450-440 Ma, ~75% species lost; second biggest extinction.

Question 2

Describe the Devonian extinction:

• Common theories for cause
• Life forms wiped out
• Characteristics of climate
• Characteristics of atmosphere
• How long ago, what % lost

Answer 2

• Possibly caused by anoxia in ocean, global cooling, and rising sea levels;
  
  • Promoted weathering of rock releasing nutrients into oceans causuing algal blooms decreasing O₂ content
  • Photosynthesis/ silicate sequestering absorbs CO₂
• Largest impact on marine groups; armoured fish vanish completely
  
  • Plants/ insects suffered little
  • Shallow tropical oceans suffered, reefs ceased to exist.
• Climate warm, dry.
• Atmosphere high O₂/ low CO₂
• 375-360 Ma; ~70% of all species lost.

Question 3

Describe the Permian extinction:

• Common theories for cause
• Life forms wiped out
• Characteristics of climate
• Characteristics of atmosphere
• How long ago, what % lost

Answer 3

• Volcanism (Siberian Traips) and platonic activity causing greenhouse affect, temperature increase, ozone layer destroyed, acid rain, dramatically increased temperatures
• Single worst extinction event (“The Great Dying”): 70% land species, 95% marine species lost.
• Climate was hot, dry (desert) in northern hemisphere/ cold in southern hemisphere with dramatic seasonal changes
• O₂ levels dropped from high point, while CO₂ levels increased
• 250 Ma; 95% of all species lost

Question 4

Describe the Triassic extinction:

• Common theories for cause
• Life forms wiped out
• Characteristics of climate
• Characteristics of atmosphere
• How long ago, what % lost

Answer 4

• Maybe least understood cause: falling sea levels, extreme temperatures, due to volcanic rift forming betweeen America/ Africa & Europe (Central Atlantic Magmatic Province)
• Many dinosaur groups, reptiles, and amphibians disappeared
  
  • Reef ecosystems and other invertebrates badly affected
• Climate was hot and dry, and received heavy rainfall on a seasonal basis.
• Greenhouse atmosphere caused by CAMP
• 200 Ma; 70-75% species lost

Question 5

Describe the Cretaceous extinction:

• Common theories for cause
• Life forms wiped out
• Characteristics of climate
• Characteristics of atmosphere
• How long ago, what % lost

Answer 5

• Cause undecided; best idea is asteroid impact shooting dust/sulfer/CO₂ into atmosphere blocking sunlight
  
  • Or maybe incerased volcanism, or both?
  • Sea levels dropped/ ocean acidification
  • Increased temperatures
• Dinosaurs previously dominated land/oceans; large dinosaurs wiped out
  
  • Small dinosaurs left behind, evolved into birds
• Climate was humid, high sea levels with many inland seas
• 66 Ma; 75% species

Question 6

List the stable isotopes of oxygen - “sizes” and abundance

Answer 6

Oxygen-16: “light” 8 protons, 8 neutrons

Oxygen-18: “heavy” - 8 protons, 10 neutrons

Oxygen-16 most naturally abundant

Question 7

Why is oxygen-18 important?

Answer 7

Ratios of oxygen-18 and oxygen-16 vary based on climate - can infer past climate based on ratios in sediments, ice cores, fossils.

High oxygen-18 concentratoins infer ice age b/c oxygen-16 is evaporated and deposited in ice sheets first - leaving behind oxygen-18.

Question 8

Describe the Yougner Dryas event.

Answer 8

~12,900 years ago very cold period, due to…

Cold, fresh water concentrations from melting glaciers interrupts thermohaline conveyor:

• Slowing down movement of warm water
• Result in cooler temperatures, because temperatures all stay constant

Question 9

Describe the Holocene Max

Answer 9

Warm period, due to… Milankovitch cycles

Question 10

List some greenhouse gases

Answer 10

• Water vapor
• CO₂
• Methane
• Nitrous oxide
• Ozone

Question 11

Describe the greenhouse effect.

Answer 11

Greenhouse gases reflect heat (infrared photons/ long-wave) back onto surface, holding heat onto planet.

Question 12

What is obliquity?

Answer 12

The tilt of the Earth’s axis; changes every 41,000 years.

Question 13

What is precession?

Answer 13

Changes in direction of tilt of rotation axis; changes very 23,000 years

Question 14

What is eccentricity?

Answer 14

Changes in shape of orbit due to magnetic attraction of planets; changes every 100,000 years

Question 15

What is current state of Milankovitch cycle?

Answer 15

• Northern hemisphere pointed toward sun (~23.5 degrees)
• Southern hemisphere pointed away from sun
• Results in mild winters/ cool summers for northern hemisphere
• Cooler winters/ warm summers for southern hemisphere

Question 16

How do tectonic plates form?

Answer 16

Cracks on Earth surface formed by cooling of Earth

These cracks form Earth’s tectonic plates

Question 17

Why are tectonic plates moving?

Answer 17

Warm, semi-liquid layer moves the plates on top (“rafting”)

Question 18

Describe ridge push.

Answer 18

Rising warm liquids creates pressure on crust (convection)
Applies pressure, and causes crust to rise (ridge)
Rising of crust causes tension, with slopes on either side
Cracks result
Magma injected into crust through cracks, can create magma chambers
Lava erupts through top of ridge, rolls down sides of slope
Solidifying magma adds weight to the system

Question 19

Describe slab pull.

Answer 19

Denser/ older material will subduct underneath younger/ less dense material.

Question 20

Describe pieces of evidence for support of Plate Tectonic Theory:

Answer 20

• Seafloor rock dating shows youngest rocks at ridges in middle of oceans, oldest rocks furthest away from ridges
• Similar fossil record found on different continents
• Magnetism (sea floor)
• Hot spots (Hawaii islands)
• Observation of actual movement via GPS

Question 21

List 3 possible outcomes of plate interactions:

Answer 21

• Divergent plate boundaries have magma creating new crust (North Atlantic Ridge)
• Subduction boundaries have oceanic crust sinking underneath continental; or oceanic crust sinks under other oceanic crust (denser rock subducts)
• Transform boundaries have plates that just slide past one another

Question 22

Describe the relationship between accretion and orogeny

Answer 22

• Accretion occurs when loose sediments are scraped onto plate above the plate subducting
• More accreted terrain results in more mountain building (orogeny)
  
  • Entire “mountains” can be accreted onto plates as well

Question 23

Describe how the earth and moon formed

Answer 23

• Earth:
  
  • Material strike together growing Earth
  • Iron melts and begins to sink
  • Lighter materials concentrate closer to surface
  • Layers evolve
• Moon:
  
  • Mars-sized impactor strikes early Earth
  • Blows off material that will collect to form moon

Question 24

Describe the rock cyle:

Answer 24

• Igneous rock cools/forms
• Weathers to form regolith
• Erodes to form sediment
• Deposited to form loess, till, alluvium
• Buried to become strata
• Lithifies to become sedimentary rock
• Metamorphosesis to become metamorphic rock
• Melts to form magma
• Crystallizes to form igneous rock

Question 25

Describe some key parts of the water cycle:

Answer 25

* Evapotranspiration: water transferred from land to atmosphere by evaporation from surfaces and by transpiration from plants * Evaporation/Condensation/Sublimation * Convection/Advection: the movement of some quantity via the bulk flow of a fluid * Infiltration/Percolation: passage of water through ground surface, and into water table, respectively

Question 26

Describe some key parts of ntirogen cycle:

Answer 26

* Nitrogen Fixing - bacteria in soil/roots which converts nitrogen gas to ammonium * Ammonia - * Nitrates/Nitrites -ammonium converted to nitrite, followed by the nitrite to nitrate, followed by denitrifying bateria converts back into atmosphere by plants

Question 27

Describe the the composition, state of matter, depth, and density of each earth layer

Answer 27

* Crust: * Oceanic: 10 miles deep, silicate, solid, 3.0 g/cm3 * Continental: 20 miles deep, silicate, solid, 2.7 g/cm3 * Lithosphere: 35 miles deep, 3.3 g/cm3, Silicates with Fe and Mg, Solid * Asthenosphere: 125 miles deep, 5.7 g/cm3, Silicates with Fe and Mg, Plastic (Behaves like a liquid; but not “fully” liquid due to various melting points of composition) * Mesosphere: 1790 miles deep, 9.9 g/cm3, Silicates with Fe and Mg, Solid (Because of the increased pressure, keeps state to solid) * Outer core: 3160 miles deep, 12.0 g/cm3, Iron and Nickel, Liquid * Inner core: 395 0miles deep, 13.0 g/cm3, Iron and Nickel, Solid