Deck 10: Major Geochemical Cycles

Question 1

Carbon dioxide is needed to weather away both

A) oxidized and reduced organic matter.
B) limestones and silicate rocks.
C) calcium and magnesium silicates.
D) animal and plant matter.

Answer 1

B

Question 2

At any time in Earth's history when the rate of carbon burial increases on continents or beneath the sea, both carbon dioxide in the atmosphere and carbon dioxide dissolved in the ocean become enriched in

A) carbon 14.
B) carbon 13.
C) carbon 12.
D) all isotopes of carbon.

Answer 2

B

Question 3

In discussing stable isotopes, which are used to study global chemical cycles, the symbol $\delta$ is used to relate the isotopic composition of

A) istopically heavy to istopically light samples.
B) istopically light to istopically heavy samples.
C) unknown samples to a standard sample to which all others are compared.
D) unknown samples to the average of all samples for the study at hand.

Answer 3

unknown samples to a standard sample to which all others are compared.

Question 4

Deep marine carbon dioxide is returned to the atmosphere by

A) melting of methane hydrates.
B) volcanoes that form along subduction zones.
C) metamorphism of limestones.
D) thermal processes along mid-ocean ridges.

Question 5

Reservoirs expand and contract because of changes in the rate at which they gain or lose their contents, and this occurrence is known as

A) flux.
B) feedback.
C) respiration.
D) photosynthesis.

Question 6

Some dead plant material escapes from the photosynthesis-respiration cycle by __________ and thus becomes a reservoir for __________.

A) decomposition; oxygen compounds
B) burial; oxygen compounds
C) burial; reduced carbon compounds
D) decomposition; reduced carbon compounds

Question 7

The most important greenhouse gas is

A) phosphorus.
B) oxygen.
C) nitrogen.
D) carbon dioxide.

Question 8

A plant requires only __________ to build tissues as it goes from a spore or seed to a larger plant.

A) carbon dioxide
B) sugars
C) water
D) oxygen

Question 9

__________ is a by-product of photosynthesis.

A) Water
B) Sugars
C) Oxygen
D) Carbon dioxide

Question 10

Isotopically light carbon that __________ preferentially extract from the atmosphere is returned to the atmosphere through the respiration of __________.

A) animals; decomposers and plants
B) plants; decomposers and animals
C) decomposers and plants; animals
D) decomposers and animals; plants

Question 11

Photosynthesis requires two things, and they are

A) nitrogen and phosphorus.
B) water and carbon dioxide.
C) silicon and oxygen.
D) iron and magnesium.

Question 12

Carboniferous fossil fuels were formed in

A) river channels.
B) deep marine areas.
C) shallow marine settings.
D) swamps.

Question 13

Chemical weathering processes on land use up __________ from the atmosphere.

A) oxygen
B) carbonic acid
C) carbon dioxide
D) sulfur

Question 14

Oxygen isotopes in bivalve shells show a seasonal layering that has different oxygen isotopic compositions: __________ during __________ and the reverse for __________.

A) heavier; winter; summer
B) lighter; summer; winter
C) heavier; summer; winter
D) lighter; winter; summer

Question 15

Glaciers are isotopically light, so contraction (melting) of large glaciers puts more __________ into the oceans and atmosphere.

A) light carbon
B) heavy oxygen
C) light oxygen
D) heavy carbon

Question 16

A sudden pulse toward __________ carbon isotopic values in the marine stratigraphic record can indicate an episode of __________.

A) light; increased burial of carbon dioxide
B) light; increased burial of organic carbon
C) heavy; increased burial of organic carbon
D) heavy; increased burial of carbon dioxide

Question 17

Decomposers break down tissues by

A) photosynthesis.
B) amino acids.
C) decomposition.
D) burial.

Question 18

Only a small percentage of the sugars made by __________ are deposited in marine sediments, whereas a large percentage of sugars from __________ are deposited there.

A) terrestrial plants; marine plankton
B) marine plankton; terrestrial plants
C) marine animals; terrestrial plants
D) terrestrial plants; marine animals

Question 19

At low temperatures, organisms incorporate a relatively large proportion of __________ in their shells or bones because ions of this isotope tend to become more __________ than other common isotopes of this element.

A) oxygen 16; energetic
B) oxygen 18; energetic
C) oxygen 16; sluggish
D) oxygen 18; sluggish

Question 20

Burial of organic carbon __________ the atmospheric reservoir of __________, but also shrinks the atmospheric reservoir of __________.

A) shrinks; oxygen; carbon dioxide
B) shrinks; carbon dioxide; oxygen
C) enlarges; carbon dioxide; oxygen
D) enlarges; oxygen; carbon dioxide

Question 21

Earth's carbon 13 reaches reached an all-time high level in the atmosphere during

A) Early Paleozoic.
B) Late Paleozoic.
C) Mesozoic.
D) Cenozoic.

Question 22

Chalk is a prime example of sediment that is closely related to a change in the kind of __________ organism that secretes large volumes of __________ within a(n) "__________."

A) marine; calcite; aragonite sea
B) terrestrial; aragonite; aragonite sea
C) marine; calcite; calcite sea
D) terrestrial; aragonite; calcite sea

Question 23

Elevated Mesozoic atmospheric carbon dioxide was due to a lower rate of mountain-building and

A) increased solar output during that time.
B) unfortunate errors in how we calculate global temperatures.
C) evolution of many new types of planktonic organisms.
D) expansion of glaciers across large areas of Earth's landmass.

Question 24

Earth's "calcite seas" developed when mid-ocean ridge volumes were

A) small and sea level was high.
B) large and sea level was high.
C) small and sea level was low.
D) large and sea level was low.

Question 25

The negative shift in carbon isotope ratios at the Triassic-Jurassic boundary likely means that

A) climate was stable, so climate change is not a factor.
B) methane hydrates were melting.
C) phytoplankton became less productive.
D) bacterial respiration rates remained steady.

Question 26

We know that greenhouse warming due to methane hydrate melting has occurred several times in Earth's history because there is isotopically __________ in sedimentary materials at these levels.

A) light oxygen
B) heavy carbon
C) light carbon
D) heavy oxygen

Question 27

Carbonates that formed during Early Cambrian and again later on during Late Paleozoic through Middle Jurassic formed in

A) "aragonite seas."
B) "calcite seas."
C) an "aragonite sea" and in a "calcite sea," respectively.
D) a "calcite sea" and in an "aragonite sea," respectively.

Question 28

Despite high carbon dioxide levels, Early Paleozoic global temperatures were lower than expected due to

A) lower solar output of energy during that time.
B) errors in how we calculate global temperatures.
C) the Paleozoic greenhouse working differently than today.
D) expansion of glaciers across large areas of Earth's landmasses.

Question 29

The first negative feedback from global warming due to a rapid increase in atmospheric carbon dioxide is

A) increased global precipitation rates.
B) acceleration of the chemical reactions of weathering.
C) weathering depletes carbon dioxide from the atmosphere.
D) expansion of forest areas.

Question 30

The sharp decline in levels of carbon dioxide in Earth's atmosphere, beginning during Devonian was due to __________ during Late Paleozoic.

A) global dry conditions
B) evolutionary expansion of large plants
C) decreased global temperatures
D) widespread mountain-building