// lecture 21

Question 1

the amount of carbon in the atmosphere is always

Answer 1

tiny compared to that in ocean and rock.

Question 2

the rate of outgassing from earth is probably

Answer 2

pretty steady, but could speed up or slow down with plate tectonics or volcanism.

Question 3

the rate of weathering, and the speed of the biological pump (the rate at which life takes CO2 and makes sediment) are dependent on

Answer 3

the climate, hence a strong feedback between the atmospheric CO2 and the climate, which appears on time scales of 100’s of millions of years and also on the time scale of thousands of years during the Pelistocene (most recent) glacial ages.

Question 4

warm climate means

Answer 4

more weathering > less CO2 > cooler climate

Question 5

Cooler climate means

Answer 5

less weathering > more CO2 > warmer climate

Question 6

climate is driven towards

Answer 6

the middle by CO2 weathering feedback. a stabilizing feedback. works on a time scale of hundreds of thousands of years and relatively big climate changes.

Question 7

prokaryotes

Answer 7

single celled organism that lacks a membrane bound nucleus, e.g. bacteria, archaea.

Question 8

eukaryotes

Answer 8

life with cells with nucleus.

Question 9

life might have survived snowball earth because

Answer 9

of hydrothermal vents or cracks in the sea-ice, which could be a potential refigum for phototrophs.

Question 10

steve warrren (UW ATM S)

Answer 10

studies ice types in antarctic as a way to understand snowball earth. also grows other types of ice in labs that don’t exist on earth.

Question 11

blue ice in antarctica might be

Answer 11

the most like ice on snowball earth.

Question 12

iceball earth/hothouse cycles occurred when they did because:

Answer 12

• continents were bunched together on the equator.
• very high rate of weathering? low CO2?
• ice albedo feedback runs away and covers earth.
• weathering stops, CO2 builds back slowly.
• CO2 reaches tipping point and ice melts.
• now have high CO2, very warm climate, very high weathering rate, CO2 drops, cycle repeats.

Question 13

continental drift (wegener, 1920s)

Answer 13

last 250 million years; another major factor in the history of climate change

Question 14

movement of antarctica over the south pole

Answer 14

allowed an ice sheet to form. higher planetary albedo.

Question 15

decline in atmosphere CO2 starting 60 million years ago

Answer 15

coincides with the rise of the Himalays and Rockies (more weathering as fresh rock exposed). also a concurrent slowdown in continental drift (less volcanism, less CO2).

Question 16

closing of the isthmus of panama was the

Answer 16

last major change to the land distribution (about 4 million years ago).

Question 17

warm mesozoic (250-65 million years ago)

Answer 17

dinosaurs; 2-6 C warmer globally. poles were especially warm - mystery. evidence for polar warmth was lush ferns and alligators in siberia.

Question 18

cretaceous sea levels were

Answer 18

200 m higher than today. the entire middle of N. america was a giant seaway.

Question 19

hot climates in last 250 million years:

Answer 19

• CO2 levels were several times higher than present. know this from many lines of evidence: isotopes in rocks/fossils, examination of plant fossils, carbon cycle models. increased undersea volcano activity was likely important for releasing more CO2.
• methane hydrates (methane frozen in ice) may have been important for a couple of the warmest times in these periods. may have rapidly been released from the bottom of the ocean, increasing GHG concentrations quickly.

Question 20

cretaceous warm

Answer 20

large shallow sea in tropics, seas to both poles.

Question 21

last 35 million years (since end of early Cenozoic)

Answer 21

• earth slowly cooling.
• life retreats from poles.
• polar ice caps established.
• most recent ice ages begin ~ 3 million years ago.
• cause of decline in CO2? - Himalayas form when India collides with Asia and the fresh rock and high precipitation around mountains increased weathering (maybe?)

Question 22

cores can be drilled out of ocean sediment, lake sediment, soil, or a glacier. they contain different types of proxy climate indicators:

Answer 22

• leftover biology - pollen, leaves, shells of small sea animals.
• physical evidence - ice rafted pebbles, chemistry of sledge, sand, etc.
• isotopic evidence - abundance of various stable and radioactive isotopes.

Question 23

most elements have several

Answer 23

stable isotopes, differing only by the number of neutrons and hence the weight of the atom and the molecule of which it is a part of.

Question 24

most of the stable isotopes are

Answer 24

heavier by one neutron than their more common versions.

Question 25

their abundance varies due to mass fractionization

Answer 25

• water containing a heavy isotope will evaporate less readily and condense more readily than a lighter isotope.
• after a bunch of vapor comes off the ocean, and moves north and starts condensing, the heavier isotopes are condensed first, so the colder it gets and the more vapor is removed by condensation, the lighter the remaining sample will become. so isotopes in snow are a measure of how cold the air was when the water was condensed.
• plants prefer lighter carbon to heavier carbon, so plant material tends to be light in C13.

Question 26

standard mean ocean water (SMOW)

Answer 26

samples that are depleted in the heavy isotope have negative deltas. SMOW is thus 0%.

Question 27

ocean sediment cores

Answer 27

can get 5 million years out of them.

Question 28

why does )18 in ocean indicate more land ice?

Answer 28

• when water evaporates from the ocean, the lighter O16 isotope evaporates more readily, leaving more of the heavier O18 behind in the ocean.
• if this evaporated water does not return to the ocean, but is stored in an ice sheet, then the fractional abundance of O18 in the ocean will increase because of the removed O16.
• High O18 in the ocean sediment must mean more stored ice on land, greater land ice volume.

Question 29

ice cores

Answer 29

give variable time resolution and time depth.

Question 30

14C is produced

Answer 30

by cosmic rays hitting 14N, or by nuclear explosions in air. decays with a half life of 5,730 years.

Question 31

the 14C of coal or petroleum is

Answer 31

zero because it’s been in the ground away from the atmosphere for millions of years.

Question 32

the 13C of coal or petroleum is low because

Answer 32

plants try to avoid it during photosynthesis.

Question 33

14C and 13C are both

Answer 33

decreasing n atmospheric CO2