Earth Systems

Question 1

On a reality TV program a family with children are monitored. As the children get noisy, the parents get more mad, and as the parents get mad, the children get more noisy.

a) Draw a systems diagram for the relationship.
b) Is there a positive or negative feedback loop?
c) Is the family unstable?

Answer 1

b) + x + = + , t.f. it is a positive feedback loop
c) Positive feedback loops are unstable

Question 2

Using the planetary energy balance equation
σT⁴ = S/4 x (1-A)

Calculate the effective temperature of the Earth with an albedo of 0.8.

σ = 5.667 x 10<sup>-8</sup> W m<sup>-2</sup> K<sup>-4</sup>
S = 1370 W m<sup>-2</sup>

Answer 2

T⁴ = [S/4 x (1-A)] / σ

T⁴ = 343 W m^-2 x (1-0.8) / 5.667 x 10-8 W m^-2 K^-4

T⁴ = 1.22 x 10⁹ K⁴ = 186 K

This would be the T of a snow covered world without an atmosphere.

Question 3

Disturbing Daisyworld Again scenarios

From P1 remove lots of daisies

Answer 3

Surface T increases beyond limits of dasiy growth. They become extinct

Question 4

Disturbing Daisyworld Again scenarios

From P2 plant lots of daisies

Answer 4

Surface T decreases and daisy cover increases, then decreases, until back at P1

Question 5

Disturbing Daisyworld Again scenarios

From P2 remove a few daisies

Answer 5

T rises and daisies suffer immediate extinction

Question 6

During the deglaciation from Snowball Earth, the ice coverage and resultant lack of sites for CO2 drawdown via photosynthesis and silicate weathering enabled volcanic CO2 to build up in the atmosphere and initiate warming.

a) Using four boxes (labelled with the following terms: CO2 drawdown; surface temperature; ice coverage; area for life and weathering) and four couplings, draw a systems diagram for the process.
b) Explaining your reasoning, state whether the system represents a positive or negative feedback loop.

Answer 6

Odd number of negative couplings = negative feedback loop

Remove CO2, increase ice and cover sites where CO2 removal ocuurs

Question 7

Daisyworld has a companion planet on which all the daisies are black.

State whether an increase in black daisy coverage will increase or decrease surface temperature.

Support your answer with a systems diagram with three boxes (daisy coverage; daisyworld albedo; surface temperature) and three couplings.

Answer 7

• Increase black daisy coverage
• Decrease albedo
• Increase surface T
• Each are negative feedbacks

Question 8

Consider a scenario where a planet is heated by a star but has no greenhouse gases in the atmosphere. The planet is home to two types of organism: black daisies and white rabbits. Using the concept of coupling in each of your responses, answer the following questions:

i) Draw a graph reflecting the relationship between black daisy coverage and planet surface temperature and explain your reasoning.
ii) Superimpose a graph reflecting the relationship between surface temperature and black daisy coverage and explain your reasoning.
iii) Mark on the graph the two equilibrium states and indicate whether they are stable (negative feedback loop) or unstable (positive feedback loop).

Answer 8

Black dasiyworld scenario

iii) Equilibrium states - 2 relationships coexist:
P1 + x + = + (unstable)
P2 + x - = - (stable)

Question 9

Consider a scenario where a planet is heated by a star but has no greenhouse gases in the atmosphere. The planet is home to two types of organism: black daisies and white rabbits. Using the concept of coupling in each of your responses, answer the following:

Consider a scenario where the planet is in the lowest temperature equlibrium state before an extinction of white rabbits leads to an increase in black daisy coverage. Using either a graph or text describe how the system will react to the disturbance.

Answer 9

• Surface T and daisy coverage increases in positive feedback loops prior to Optimum T for daisy growth
• Increase in T beyond optimum T causes dasiy coverage to decrease, forming negative feedback loop
• Until at P2

Question 10

Is the stable state on black daisyworld a higher or lower temperature than on white daisyworld?

Answer 10

Stable state for black daisyworld at higher temperature

Question 11

i) Draw a graph reflecting the relationship between black daisy coverage and planet surface temperature and explain your reasoning.
ii) Superimpose a graph reflecting the relationship between surface temperature and black daisy coverage and explain your reasoning.

Answer 11

i) As black dasiy coverage increases, albedo decreases and surface T increases as more radiation can be absorbed
ii) Plants have an optimum growth temperature, resulting in an overall parabolic relationship between surface T and daisies.

This results in positive coupling below optimum (increase in T = increase in daisies), and negative coupling above optimum (increase in T = decrease in daisies).

Intersections represent two equilibrium states, where 2 relationships coexist

Question 12

Explain how introducing more white daisies to Dasiyworld affects surface temperature.

Answer 12

Question 13

This question is about the carbon isotopic record of atmospheric carbon dioxide levels in the Phanerozoic.

In the table, why are the values for d13C marine carbonate rock and d13C paleosol carbonate different for deposits of the same age?

Answer 13

• Carbon dioxide in marine water is primarily from one source, i.e. dissolved gas from the atmosphere.
• Calcium carbonate can ppt or be assimilated by organisms from marine water.
• d13C of carbonate rock faithfully maintains a constant relationship with d13C of the atmosphere.
• By contrast, carbon dioxide in soil water and air is a mixture of two sources.
• Some CO2 in soil water and pore spaces has diffused directly from the atmosphere while some is from the respiration of plants and bacteria.
• Isotopically, the two sources are distinct, atmospheric co2 is enriched in the heavier carbon isotope 13C whereas respired co2 is enriched in the lighter carbon isotop 12C

Question 14

This question is about the carbon isotopic record of atmospheric carbon dioxide levels in the Phanerozoic.

Explain how can d13C values of paleosol carbonate reveal past changes in atmospheric CO2 levels.

Answer 14

• When atmospheric co2 levels are high, more diffuses into the soil and, conversely, when atmospheric co2 levels are low, less diffuses into the soil.
• The stable isotopic effects of the two situations are that low atmospheric co2 levels give more negative d13C values for soil carbonate and high atmospheric co2 levels give more positive d13C values for soil carbonate.

Question 15

Describe the relationship between d13C marine carbonate rock (d¹³C_carb) and the global fraction of buried organic carbon (f_org).

Explain how this relationship is maintained.

Answer 15

• Heavier d13C values for carbonate rocks indicate periods of time when more organic carbon is buried.
• d13C of organic matter is enriched in the lighter carbon isotope and therefore its burial removes amounts of 12C from circulation.
• A residual enrichment in 13C is left behind leaving heavier d13C values in the atmosphere and surface ocean.

Question 16

Which is the most reliable data source, d13C marine carbonate rock or d13C paleosol carbonate, for reconstructing past atmospheric carbon dioxide levels?

Answer 16

d13C carbonate is a more reliable data source for reconstructing past atmospheric carbon dioxide levels bc it involves fewer variables and assumptions.

Question 17

What are the variables involved in the use of d13C palaeosol carbonate for reconstructing past atmospheric carbon dioxide levels?

Answer 17

• isotopic change induced by variations in
  
  • soil T,
  • moisture,
  • porosity and
  • plant respiration rates.

Question 18

What are the assumptions involved in the use of d13C palaeosol carbonate for reconstructing past atmospheric carbon dioxide levels?

Answer 18

• That increased atmospheric co2 levels result in greater amounts diffusing into soil, and
• That amounts of respired co2 present in paleosols can be reliably estimated.
• That d13C plant co2 hasn’t changed over time. In this context it is interesting to note that d13C palaeosol carbonate can’t be used after 14 Ma bc of the evolution of an additional photosynthetic pathway illustrating that d13C plant co2 does change.
• Atmospheric co2 hasn’t changed in d13C over time. This assumption is clearly suspicious as the d13C marine carbonate rock values in the table indicate that d13C atmospheric co2 has changed significantly during Earth’s history.

Question 19

Using the figure, explain the stable isotopic composition of hamburgers.

Answer 19

Reflects meat fed on a food source other than corn

Question 20

Using the figure, explain the stable isotopic composition of chicken.

Answer 20

Reflects meat fed on a corn food source

Question 21

Using the figure, explain the stable isotopic composition of chicken nuggets.

Answer 21

Reflects a mixture of corn-fed meat and other materials such as breadcrumbs

Question 22

Add to the figure to indicate:

i) A human population existing exclusively on hamburgers
ii) Nursing infants from the same population

Answer 22

Question 23

How could the data in the figure be used to determine the habitat of a human population?

Answer 23

Based on food sources. E.g. corn grows in hot climates, fish diets reflect proximity to coastline.

Other diets reflect temperate inland locations.

BS!!!!!!!!!!!!!!!!!!!!!!

Question 24

Re: stable isotopes and space

Use plot to assign source regions for:

Sample A: dD -50; d13C -25
Sample B: dD 127400; d13C 435
Sample C: dD 1439; d13C -16.7

Answer 24

Question 25

Re: stable isotopes and space

List samples A, B and C in order of increasing sample processing. Explain your reasoning.

Answer 25

1. Sample B: Interstellar material
2. Sample C: Meteorite macromolecule
3. Sample A: Earth organic matter

Reflecting degree of chemical and physical processing.

Question 26

What is a system?

Answer 26

A system comprises interrelated components functioning as a complex whole

Question 27

What is a component?

Answer 27

Individual part of a system or sub-system

Question 28

Define ‘state’

Answer 28

Nature of a system at any point in time

(set of attributes - e.g. room t, noise level, etc)

Question 29

What is coupling?

Answer 29

• Link between system components
• Change in one component results in a change in the same direction for another

Question 30

What is a positive coupling?

Answer 30

Change in one component results in a change in the same direction for another

Question 31

What is a negative coupling?

Answer 31

Change in one component results in a change in the opposite direction in another

Question 32

What is a feedback loop?

Answer 32

• Self-perpetuating mechanism of change and response.
• Negative feedback loops diminish effects of disturbance.
• Positive feedback loops amplify effects of disturbance.

Question 33

What determined whether a system is in the equilibrium state?

Answer 33

• Negative feedback
  
  • Stable
  • Equilibrium state
• Positive feedback
  
  • Unstable
  • Slightest disturbance
  • System driven away from equilibrium
• Imagine all possible states as a hilly surface where valleys represent stable states and hills, unstable states; with a ball being the current state.

Question 34

Imagine all possible states as a hilly surface where valleys represent stable states and hills, unstable states; with a ball being the current state.

Describe a stable equilibrium state.

Answer 34

• The ball can roll back into a stable state in the valley after a small disturbance with a nehative feedback loop diminishing effects of the disturbance (states controlled by negative feedbacks are stable).
• A large disturbance can force system into new equilibrium state (over the hill, into next valley).

Question 35

Imagine all possible states as a hilly surface where valleys represent stable states and hills, unstable states; with a ball being the current state.

Describe an unstable equilibrium state.

Answer 35

• Ball starts at the top of a hill
• After small disturbance ball accelerates until in new position (no negative feedback to move back to previous position)
• Positive feedback enhances effects of disturbance - rapid change until new state is found
• States controlled by positive feedbacks are unstable

Question 36

What is the evidence for Snowball Earth (750 to 580 Ma)?

Answer 36

• Glacial deposits (tillites) on all continents, all latitudes.
• Laterally extensive marine sediments indicating anoxia (Banded Iron Fms deposited in absence of oxygen).
• Rapidly replaced by non-glacial, warm, shallow marine “cap” carbonates, indicating rapid transition from cold to warm conditions.

Question 37

Explain the first stage system of Snowball Earth evidenced by glacial deposits.

Comment on whether it’s in a positive or negative feedback loop.

Answer 37

Question 38

Explain the second stage system of Snowball Earth evidenced by BIFs.

Answer 38

Question 39

During Snowball Earth, how did the “loop” get reversed?

Answer 39

Question 40

Explain the thrid stage system of Snowball Earth evidenced by “cap” carbonates.

Answer 40

Question 41

Describe the Freeze-Fry scenario

Answer 41

• Single snowball cycle
  
  • Ice reaches 30°
  • Runaway albedo
  • CO2 build up
  • Runaway greenhouse
  • CO2 drawdown
    
    • Silicate weathering
    • Photosynthesis

Question 42

Celebrity couple Katie Bryce and Peter Andrew have individual electric blankets with dedicated temperature controllers. Despite repeated attempts by Katie and Peter to change the temperature of their blankets, Katie remains too cold and Peter feels increasingly warm. Draw a systems diagram to illustrate how this situation may have come about. Indicate any positive or negative couplings, discuss whether positive or negative feedback loops are operating and state whether the celebrity couple are in a stable or unstable condition.

Answer 42

Question 43

Describe the basic theory of stable isotopes

Answer 43

• Stable = they are not radioactive
• Isotopes
  
  • Chemically identical
  • same number of electrons and protons
  • different masses
  • different number of neutrons
• Occurence, different relative abundances
• Effects
  
  • Different masses, different bond frequencies, affects zero points
• ​Lighter isotopes, smaller energies needed = more reactive

Question 44

In the context of stable isotopes, what is zero point energy?

Answer 44

• Zero point energy
  
  • lowest possible energy a system can have
  • non-zero ground state
  • vibration never zero
• Isotopes have different zero-point energies
  
  • e.g. hydrogen bonds

Question 45

Explain how carbon isotopes reveal Earth system processes

Answer 45

• Carbon isotopes take two different forms in the Earth system, C-12 and C-13, in different relative abundances.
• Carbon reservoirs are oxidised and reduced.
• Photosynthesis uses C-12 preferentially; sinking and burial stores C-12.
• Less C-12 for carbonates or further OM production.
• C-13/C-12 ratio reflects rate of production, sinking and burial.
• Ratio of sample compared to a standard:

d¹³C (%_o) =
​[(¹³C/¹²C_spl - ¹³C/¹²C_std) / (¹³C/¹²C_std)] x 1000

Question 46

How have carbon isotopes changed through Earth time?

Answer 46

• Carbon isotope records (d13C carbonates, d13C organic) reflect reservoir sizes.
• ~Constant values for at least 3.5 Ga
• Notable events at 2.1-1.8 and 1.0-0.7 Ga.
• Causes
  
  • Rifting and orogeny
  • Clastic supply
  • Nutrient supply
• Productivity and organic deposition

Question 47

What were the causes for d13C_carb and d13C_org variations during the neoproterozoic?

Answer 47

• Major biological events
• Major depositional events
• Volcanism
• Weathering
• Proterozic ice age
  
  • Drop in productivity
  • Decline in d13C

Question 48

What were the causes for major d13Ccarb variations during the Phanerozoic?

Answer 48

• Significant d13Ccarb variation
• Major depositional events
• Volcanism
• Weathering
• e.g. Silurian-Devonian - increased silicate weathering; marine regression; land plants
• e.g. Carboniferous - evolution of biopolymers; organic deposition; increase in d13C

Question 49

Indicate how carbon isotopes in paleosols reveal palaeoenvironmental information

Answer 49

• Using a simple mixing ratio:
• Plants (are a carbon reservoir and) take in C-12 preferentially, produce OM which is sometimes buried.
• Some of this OM after its production during photosynthesis is used for energy, e.g. starch, carbohydrates. This energy source is is used for bio-chemical machinery of life.
• T.f. OM comes from CO2 and water, passes through metabolism, and some is respired and converted back to CO2 and water - with the release of energy being the only thing that changes.
• The respired CO2 (rich in light C-12) is either released into the atmosphere or into the soil.
• (The C-12 released acts as a tracer of the source of the C.)
• T.f. part of the C in the soil is C-12 from respiration.
• Additionally, atmospheric CO2 percolates into the soil (into the pores, gaps and cracks), t.f. producing a mixture of respired CO2, rich in C-12, and atmospheric CO2, richer in C-13.
• Diagnostically, the important thing is you get more CO2 from the atmosphere incorporated into the soil when atmospheric CO2 levels are high.
• T.f. when measuring the isotopic composition (d¹³C; ratio of C-13 to C-12) of the paleosol, the values tell of the mixing ratio between respired and atmospheric CO2 - assuming that plants are producing the same amount of respired CO2 through time, and any variation is due to atmospheric CO2 input, related to the pressure of CO2 in the atmosphere.

Question 50

Outline/indicate how stable isotopes aidd forensic studies

Answer 50

• Used to determine steroid abuse:
• Use d13C to determine what a person has admistered vs what is produced naturally in the body.
• For e.g., an athlete may administer anabolic steroids for performance enhancement purposes.
• World Anti-Doping Agency
• Athletes no longer take exogenous steroids (e.g. Stanozol) bc it’s not present naturally in the body and can be easily found out.
• Most common anabolic steroid taken amongst athletes is t.f. testosterone (also androgenic) to supplement the testosterone levels already in the body.
• Bc it is produced naturally in the body (it’s endogenous), its structure cannot be used to determine whether a person is doping, but the source of the synthesised testosterone is not anthropogenic, its botanic, and so the d13C can be used.
• Stigmasterol generated in plants can be transformed into testosterone pharmacutically - plants are rich in C-12, and humans are not due to their varied diets.
• Synthetic steroids produced in this way have a similar d13C to C3 plants.
• T.f. if, from a blood or urine sample the steroid compounds (e.g. testosterone) have (i) a d13C identical to/similar to C3 plants; and (ii) different/lighter d13C compared to the d13C of indigenous reference compounds, then GUILTY.
• Indigenous reference compounds are steroids produced naturally in the body, like cholerserol, that don’t posses any performance enhancing capabilities and would t.f. not be administered and posses the d13C produced naturally within the person’s body.
• I.e. if testosterone is C-12 rich, and cholesterol is more C-13 rich - GUILTY.

Question 51

How are organic compounds extracted from meteorites?

Answer 51

• Extraction
  
  • Supercritical fluid extraction (SFE)
  • Retains volatiles
  • Efficient/selective
  • Contaminant free
• Pyrolysis
  
  • Hydrous pyrolysis
  • Thermal decomposition
  • >300°C & 72 hrs
  • Liquid water
  • High yeilds

Question 52

Carbon isotopes in meteorites indicate preterrestrial mechanisms.

Describe/dicuss the meteorites in question.

Answer 52

• Meteorites are fragments of asteroids that are unprocessed and posses 4.6 Byr old matter, from the birth of the solar system.
• There will be fractions that pre-date the solar system, with d13C beyond the signatures of our solar system (interstellar signatures).
• Carbonaceous chondrites are primitive meteorites, possesing 2-5% OM (25% solvent soluble, “free”; 75% insoluble, macromolecular) with varied d13C.
• This meteoritic organic matter holds record of solar system evolution (preceeding asteroid formation) and several environments (e.g. interstellar could, solar nebula).
• E.g. Murchison
• It is important to know if the d13C’s are true or are from terrestrial contamination.
• Also, the presence of a mixture of large and small, and stable and unstable organic componds reflects its unprocessed nature.

Question 53

It is important to know if the d13C’s of meteorites are true or are from terrestrial contamination.

What d13C characteristics do meteorites posses?

Answer 53

• high d13C of 20-25 in meteorite amino acids;
• relatively high d13C of -10 in organic C compared to earth materials;
• really high CO₂ and carbonate d13C of 30-50;
• also high dD (deuterium) is a non terrestrial signature, 1000-2500 in meteorite amino acids.

Question 54

What d13C reaction mechanisms take place within Murchison organic compounds during pyrolysis?

Answer 54

• Aromatic hydrocarbons become enriched in C-12 down the reaction sequence as the carbon number is increased (building more complex C compounds from simpler precursors), i.e. making bonds >12C in products (synthesis)
• Also show the opposite in a “cracking reaction”, where breaking bonds >12C in products, and larger starting materials break into smaller compounds.
• In either case, C-12 always becomes more enriched in the reaction product.
• So have opposite reactions taking place from central point.
• The same/similar trend is followed in the macromolecules, the major organic component of the meteorite.
• The processes are indicated as such bc stable isotopes are good for indicating whether similar processes take place in different compounds, bc the sources are the same - they are genetically linked.
• However, free compounds always slightly more C-12 enriched (determined by comparison vs pyrolysis fragments of macromolecular material).

Question 55

Explain how the carbon isotopoic signature of the Murchison meteorite indicates preterrestrial mechanisms.

Answer 55

• Free aromatics, from pre-terrestrial generation, have lighter d13C than pyrolysate aromatics generated at present day in the lab.
• Pyrolysate aromatics t.f. have more C-13 enriched reservoir.
• This demonstrates that the macromolecules present in the asteroid started to break down at some point in the pre-terrestrial past and became more enriched in C-12 during the reaction.
• The same sample, in modern day, is taken to the lab and the macromolecule is broken down again, extending the degredation process.
• But bc the lightest C has already gone, the second attempt is slightly more enriched in C-13.

Question 56

Explain mass dependent fractionation.

Answer 56

• If an element has more than one rare stable isotopes (e.g. 16O, 17O, 18O) the fractionation patterns of the two rare isotopes is predictable.
• Based soley on mass effects, the amount of fractionation increases as the mass increases.
• Example: If a reaction isotopically discriminates against 18O it will discriminate less for 17O, by roughly a factor of 2.
• So, based soley on mass-dependent fractionation, if you know the d18O, then you also know the d17O. The slope of a d17O vs d18O plot is 0.5.
• So what are the points that fall off the mass-dependent line…?

Question 57

Explain mass independent fractionation.

Answer 57

• Mass-independent fractionation refers to any process that seperates isotopes, that does not scale in proportion with the difference in the masses of the isotopes.
• Mass-independent fractionation processes are uncommon, occuring mainly in photochemical and spin-forbidden reactions.
• Found mainly associated with atmospheric chemistry, effect can be preserved as many geochemical reactions in water and rock are mass-dependent.

Question 58

Describe the multiplication rules that help define positive and negative feedback loops.

Answer 58

• Negative feedback loops have an odd number of negative couplings (- x + = -)
• Positive feedback loops have only positives or an even number of negative couplings (- x - ; or, + x +, = +)

Question 59

Define the term primary atmosphere.

Answer 59

An atmosphere that exists immediately after the planet’s formation

Question 60

Define the term secondary atmosphere.

Answer 60

Forms after the primary atmosphere is lost

Question 61

Briefly discuss/introduce the various theories of primary atmosphere formation.

Answer 61

• Primary atmospheres form from earliest solar system, 4.56 Ga
• Giant disk of dust and gas
• Planets formed by positive feedback of accretion and gravitational attraction
• Dust grains to larger bodies
• Larger bodies had atmospheres
• The origin of gas has a combination of four possible mechanisms:
  
  • Solar nebula theory
  • Accretion theory
  • Solar wind theory
  • Comet/asteroid theory

Question 62

Briefly describe and evaluate the solar nebula theory of primary atmosphere formation.

Answer 62

• Gravitational attraction
• Gas from solar nebula
• Requires planets to grow quickly, before nebula gas dissipates within 10 Myr of nebula lifetime
• Earth & Venus
  
  • 60% Earth’s mass in 10-20 Myrs
  • Long enough to capture substantial atmosphere
• Mars
  
  • Smaller
  • Uncertain if massive enough

Question 63

Briefly describe the accretion theory of primary atmosphere formation.

Answer 63

• Volatiles carried into the growing planets by infalling planetesimals and dust
• Easily driven out with heating
• Gases released from minerals as planets heated up
• Contributions would be similar to those found in primitive meteorites
  
  • H₂O, CO₂, N₂, CH₄, NH₃

Question 64

Briefly describe the solar wind theory of primary atmosphere formation.

Answer 64

• Atmospheres caught from solar wind
• Plasma (primarily protons and electrons with ionised gas of many elements)
• 300 km s-1
• 1000 km s-1 during flares

Question 65

Briefly describe the comet/asteroid theory of primary atmosphere formation.

Answer 65

• Volatile-rich comets and asteroids
• Late veneer

Question 66

What does the chemistry of the Earth’s volatiles tell us about their origin?

Answer 66

• Outer earth reservoirs = atmosphere, hydrosphere and crust.
• Earth volatiles (relative) different from Sun - fractioned relative to Sun; Similar to chondrites
• Other similarities to chondrites = atmosphere noble gases; Earth D/H
• Differences from chondrites = absolute abundances lower, xenon depleted.
• Chondritic source: asteroid belt, kuiper belt, giant planet regions - final stages of Earth formation

Question 67

Outline the various ways in which secondary atmospheres are formed.

Answer 67

• Secondary atmospheres evolved from, or after, primary atmospheres.
• Several mechanisms:
  
  • Atmospheric loss (thermal and hydrodynamic escape and other)
  • Outgassing from interior (volcanic eruptions, juvenile gases)
  • Crustal interactions (weathering, CO2 to carbonate, condensation of H2O into ice)
  • Photochemistry
  • Photosynthesis (LIFE a major contributor)

Question 68

Explain how thermal escape can cause the formation of secondary atmospheres.

Answer 68

• Higher T’s, more rapid movemements
• Distribution of speeds
• Exceptionally fast gas molecules can escape pletary gravity
• This is critical speed is called the escape speed
• Earth’s atmosphere
  
  • No lid so molecules moving faster than escape speed are lost continually
  • All planets are constantly losing a proportion of their atmospheres

Question 69

What are the thermal escape variables?

Answer 69

• Temp: Hotter atmospheres have greater average molecular speeds, higher chances of molecules leaving
• Molecular size: molecules have different masses; average speed for one gas will be different from another
• Planetary gravity: bigger planet can hold on to smaller molecules; Mars - CO2; Jupiter H2
• Implication: A planet’s atmopshere can change through time bc of physical processes

Question 70

In the context of thermal escape, what is ‘Jean’s observation’?

Answer 70

For a planet to retain a gas over time, mean speed of molecules must be less than one sixth escape speed

Question 71

Explain how hydrodynamic escape can cause the formation of secondary atmospheres.

Answer 71

• Intense extreme UV radiation
• Hydrogen expands at supersonic speeds
• Exerts forces on heavier molecules (push; pushes them out)
• Lighter molecules entrained (drag; drags them out)
• Notable occurances: Pluto, Triton (Neptune’s largest moon)

Question 72

Explain how the other escape mechanisms can cause the formation of secondary atmospheres.

Answer 72

• Atmospheric cratering (molecules reach escape speed during impact) e.g. Mars 50-90% loss; Earth in Moon forming event
• Solar wind (ionization of heavier gases by solar UV; CO, N2; convected in the magnetosphere) e.g. Mercury’s gases lost this way

Question 73

Explain how the volcanic outgassing can cause the formation of secondary atmospheres.

Answer 73

• Terrestrial planets have “volcanic” atmospheres
• Volcanic gasses are water rich
• Without water they look planetary, similar to Mars and Venus
• Valid comparison - most water is cycled near surface

Question 74

Explain how the crustal interaction can cause the formation of secondary atmospheres.

Answer 74

• Silicate weathering
• Carbonate ppt
• Combination of these two reactions results in one CO2 molecule being removed from the atmosphere

Question 75

What caused the Earth’s atmosphere to change around 4.5 - 3.8 Ga?

Answer 75

• Hadean Earth
• 4.5 - 3.8 Ga oceans formed
• CO2 dissolves in water
• CO2 removed from atmosphere by rain
• Drop in atmospheric CO2

Question 76

Explain how the photochemistry can cause the formation of secondary atmospheres.

Answer 76

• E.g. photolytic dissociation
• Water was a source of oxygen on prebiotic Earth
• 2H₂O + UV → 2H₂ + O₂
• 10^-12 to 10^-14 present atmospheric level
• Some products recombine
• 2H₂ + O₂ → 2H₂O
• Often light products (e.g. H₂) are permanently lost to space (Venus lost all its water this way; Earth lost a third of its water this way)
• Auto-oxidation of carbon dioxide
  
  • 2CO₂ + UV → 2CO + O₂
  • Mars 0.13% O₂ formed this way

Question 77

Explain how the photosynthesis can cause the formation of secondary atmospheres.

Answer 77

• Photosynthetic organisms capture sunlight and transform in into organic compounds
• Organic compounds fuel the biosphere (stored energy is released via respiration)
• To oxygenate the atmosphere the cycle must be interrupted
• Each carbon atom buried releases one O₂ molecule

Question 78

How does the Sun generate its energy and how does this process evolve over long periods of time?

Answer 78

• Nuclear fusion (4 x ¹H = ⁴He)
• Long term evolution
• Fusion gives volume reduction, but core does not shrink - heats up to maintain pressure
• Higher core T’s (increase reactions, faster rates of fusion, higher energy output)
• Luminosity (hydrogen fuel depletion, luminosity (brightness) increases)

Question 79

What is the Faint Young Sun paradox?

Answer 79

The Faint Young Sun paradox describes the evidence for liquid water at the surface of the Earth during the Archaean despite the Sun being about 25-30% less luminous

Question 80

What evidence suggests that a greenhouse gas is part of the solution to the Faint Young Sun paradox?

Answer 80

Oxygenation of the atmosphere around 2.4 Ga was immediately followed by the Huronian glaciation; this suggests that atmospheric oxygen destroyed a reducing greenhouse gas.

Some greenhouse gases brought to Earth by meteorites.

Question 81

Describe the terrestrial evidence for the Faint Young Sun paradox.

Answer 81

• 3,8 Ga sedimentary rocks that require liquid water
• Life at least 3.5 Ga - requires water also

Question 82

Describe the stellar processes “evidence” for the Faint Young Sun paradox. Briefly critique some example mechanisms which may or may not resolve the issue.

Answer 82

• Suggestion that a More massive Sun, brighter in the early solar system, accounts for T difference, and that Sun mass lost since formation.
• Solar wind caused outflow of charged particles from corona
• 1% mass loss over geol time
• 10,000 too small to put into models
• Suggestion that mass lost in T-Tauri stage, which is known to cause rapid loss to young stars but only over the course of 1 Myrs!
• Earth took 10 Myrs to form, t.f. T-Tauri over too early.
• Earth-bound scenario needed!

Question 83

Discuss the proposed terrestrial solutions to the Faint Young Sun paradox.

Answer 83

• Planetary albedo
  
  • Current albedo = 0.3
  • 70% solar luminosity requires 0.0 albedo which is impossible (e.g. clouds)
• Geothermal heat sources
  
  • For radioactive decay to be a solution, 70% SL needs 70 Wm-2.
  • Modern is only 0.06 Wm-2, and it was 4-5 times this 4 Ga but that’s still not enough.
• Greenhouse effect (water vapour, but precipitates; ammonia, destroyed by UV; CO2).
  
  • Atmospheres can influence habitability
  • Planetary atmospheres can retain heat owing to the greenhouse effect
  • CO2, water, methane are all GHGs.

Question 84

Discuss the possibility of a carbon dioxide-rich atmosphere being a solution to the Faint Young Sun paradox.

Answer 84

• Fewer CO2 sinks (small continents, little silicate weathering, small carbonate stores)
• More CO2 sources (impact degassing, enhanced volcanism)
• Amounts needed:
  
  • 70% SL needs 0.3 bar, 1000 times present day
  • Carbonate reservoir = 60 bar, t.f. only 0.5% of that needed (and can assume that CO₂ wasn’t all ppt at that point)
• Ocean covered Earth - 10 bar pressure

Question 85

What conditions were present in the Hadean that would facilitate CO₂ as a solution to the FYS paradox?

Answer 85

• 10²⁰ kg surface carbonate today, assume same amount 4.5 Ga
• No continents so no land storage - atmosphere, ocean and sea floor only reservoirs
• More dissolved inorganic carbon, higher heat flux and conditions for forming carbonated basalts
• Assume 100% efficiency for carbon removal in vents, and a seafloor lifetime of 60 Ma - ocean through vents in 10 Ma.
• Carbon 6:1, seafloor : ocean
• 1/7 (15%) of 10²⁰ kg carbonate present in atmosphere + ocean:
• 0.15 x 10²⁰ kg = 0.85 x 10¹⁹ kg
• Present day 4.076 x 10¹⁶
• Hadean had 400 times more CO₂ in atmosphere and ocean than present day- GH effect

Question 86

Outline how planets can reside in habitable zones.

Answer 86

• Sun-like stars are best for habitable zones
• Flux of radiant energy from Sun is related to distance and drops by inverse-square law
• Effective T related to T of surface and atmosphere of planet
• Earth-like planet with liquid water at the surface related to luminosity and distance from star (models say 0.95 - 1.1 au).
• Would have runaway GH (& albedo) with stabalization of CO2 feedbacks (silicate weathering drops 1.5 au (near Mars))
• Star luminosity increases with time and HZ moves outwards
• There’s a continuously habitable zone that overlaps HZ at all times, CHZ narrower than HZ, 1.25 au

Question 87

What other habitable zones exist?

Answer 87

• Midway through star’s life
• Mass relative to Sun
• Distance in au
• Red star
  
  • closer than 1au
  • ca. 0.1 tidal locking
• Blue star
  
  • further than 1 au
  • short lifetime
  • hottest star 10s Ma, sun 10 Ga
  • high T, high wavelength
  • peak in UV light
  • splits O2, super ozone layer?
• Sun like stars best for HZ

Question 88

What are the sources of atmospheric oxygen?

Answer 88

Photochemistry

Photosynthesis

Question 89

Describe how photochemistry is a source for atmospheric oxygen.

Answer 89

• E.g. Photolytic dissociation (source of oxygen on prebiotic Earth)
• Water, H₂O + UV → 2H₂ + O₂
• CO₂, 2CO₂ + UV → 2CO + O₂
• Very small amounts: 10^-12 to 10^-14 present atmospheric level (PAL)

Question 90

Describe how photosynthesis is a source for atmospheric oxygen.

Answer 90

Light + nCO₂ + nH₂O → (CH₂O)n + nO₂

• Respiration, (CH₂O)n + nO₂ → nCO₂ + nH₂O + energy
• Balanced equations
  
  • Interuption of cycle
  • Burial of OM (CH₂O)n allows O₂ to accumulate
  • Each C atmon buried releases one O₂ molecule to the atmosphere

Question 91

What geological evidence is there that gives indication of past oxygen levels?

Answer 91

• Iron and oxygen
  
  • Banded iron fms
  • Red beds
• Uranium and oxygen
  
  • Detrital uraninites
  • Oklo natural reactor
• Paleosols
  
  • Iron profiles
  • Soil-rock relationships
• Sulfur stable isotopes
  
  • Mass independent fractionation

Question 92

Describe the relationship between iron and oxygen.

Answer 92

• Iron has 3 oxidation states
• Least oxidized: metallic iron, Fe; rapidly oxidised at present day.
• FeO (ferrous iron) forms under partly oxidising conditions
• Fe₂O₃ (ferric iron, haematite; Fe₂O₃.3H₂O, limonite/rust) forms under highly oxidising conditions
• Variable solubilities - Fe²⁺ soluble in water; Fe³⁺ insoluble
• Only Fe³⁺ oxides persist in nature

Question 93

What does the presence of BIFs tell of the level of atmospheric oxygen?

Answer 93

• BIFs extend over thousands of square kms.
• The iron must originally have been held in solution in the soluble ferrous state.
• Huge quantities of iron in BIFs could only have been transported into the areas in which they were deposited if the ocean was mostly oxygen-free.
• Gases readily transfer between the atmosphere and ocean.
• It follows, t.f., that at the time the atmosphere cannot have been highly oxidising.
• If it were, the oxygen-rich waters would simply cause the iron to be ppt nearer to its source.
• But process poorly understood

Question 94

During what time do we see BIFs being deposited and what does this tell us about atmospheric composition?

Answer 94

• Lots of BIF deposits older than 2 Ga (e.g. Isua group, Greenland 3.8 Ga)
• Only few BIFs younger than 2 Ga
• (On five continents between 0.7 - 0.55 Ga, Snowball Earth)
• Around 2 Ga the oxidation state of the ocean and, t.f., the atmosphere changed decisively.
• Great Oxidation Event 2.3 Ga

Question 95

What does the occurance of red beds tell us about atmospheric composition?

Answer 95

• Ancient rocks with iron oxide staining are prima facie evidence of an oxidising environment.
• No red beds older than 2 Ga (e.g. Huronian fms Ontario, Canada)
• Prior to 2.3 Ga (GOE), the oxygen content of the atmosphere was insufficient to oxidise all the iron minerals at the surface of the Earth.
• Oxygen depletion replaced by oxygen abundance.

Question 96

Describe BIFs.

Answer 96

• Rhythmic alternation of dark brown, iron-rich layers with lighter coloured, iron-poor layers
• Iron oxides make up the iron-rich bands
• Iron-poor bands consist mostly of flinty silica (SiO2), also known as chert
• Layers are of centimetre scale with sub-millimetre size microbanding
• Larger scale rhythmic banding is known in some deposits
• Individual bands only millimetres thick can be traced for tens of kilometres

Question 97

State how uranium dissolves in water at various oxidation states and, by reference to geological examples, indicate how uranium deposits reveal the oxygen content of Earth’s atmosphere through time.

Answer 97

• Uranium shows the opposite relationship to iron:
• It’s reduced form (U⁴⁺) is extremely insoluble in water, and its oxidised form (U⁶⁺) is soluble in water.
• Uraninite (f.k.a. pitchblende; U₃O₈) is a partially reduced oxide, and is not stable at the Earth’s surface today. The ore would be oxidised to its soluble form and leached away.
• 2.45 Ga detrital uraninite deposits are found at Blind River and Elliot Lake in Ontario, Canada.
• Before ~2 Ga similar deposits of uraninite occur elsewhere in the world.
• After ~2 Ga detrital uraninite deposits dissapear from the geo. record.
• Indicates a decisive change in the atmosphere, roughly coincident with that signalled by the disappearence of BIFs.
• Uraninite grains could not have survived in an oxidising atmosphere. So before 2 Ga the atmosphere must have been more reducing than the present day.

Question 98

Describe what is meant by the Oklo natural reactor.

Answer 98

• Oklo (Gabon, Africa) has 1.8 Ga Uranium ore deposits that is severely depleted in the radioactive isotope ²³⁵U, indicating that the deposit had gone ‘critical’.
• U-235 had long ago decayed to different daughter products and so a critical mass of uranium must have accumulated.
• Sufficient U-235 accumulated for chain reactions to start; neutrons from some uranium atoms caused fission of others, liberating yet more neutrons.
• The reactions continued for many years, generating gentle heat

Question 99

Describe the creation of the Oklo natural reactor and state what it meant for contemporary oxygen levels.

Answer 99

• In the present oxygen-rich atmosphere, eroded uranium is dissolved in water and transported.
• Some oxidised uranium may encounter organic material, rotting vegetation and logs of wood.
  
  • Bacterial processes use up all the oxygen, and create locally reducing conditions.
  • Uranium becomes insoluble and is deposited.
• Through time, large concentrations of uranium builds up in decomposing organic matter, sometimes within individual logs.
  
  • 1.8 Ga, the only organic matter was algal or bacterial mats
  • A concentration process was operating at Oklo, Gabon, Africa.
• T.f. @ 1.8 Ga, the atmosphere must have been oxidissing to allow transport of water-soluble uranium that was then accumulated at Oklo.

Question 100

Briefly describe what palaeosols can tell us about past atmospheric oxygen levels.

Answer 100

• Look at distribution of iron in a profile through the soil.
• Ferrous (Fe2+) iron is soluble in water and ferric (Fe3+) iron is insoluble in water.
• Whether iron is present in its ferrous or ferric state depends on whether the local environment is reducing or oxidising.
• So determining whether water has transported iron away, or left it in place, at some point in the past can tell us if conditions were oxygen-poor or oxygen-rich.

Question 101

To see how we interpret the iron chemistry of paleosols let us consider what happens when water is poured into a plant pot which contains a certain amount of iron-containing soil.

Explain what happens in reducing conditions.

Answer 101

• Water exiting from the base will contain iron in the ferrous (Fe2+) form.
• This is soluble in water and can be transported down through the soil and out through the holes.
• Palaeosols that were in contact with a reducing atmosphere when they formed will themselves be reduced and the ferrous (Fe2+) form of iron will be dominant.
• Ferrous iron is soluble in water and so percolating fluids will transport iron down through the soil profile.
• Reduced palaeosols, t.f., will have lost much of their iron from their top layers and iron will increase in abundance downwards.

Question 102

To see how we interpret the iron chemistry of paleosols let us consider what happens when water is poured into a plant pot which contains a certain amount of iron-containing soil.

Explain what happens in oxidising conditions.

Answer 102

• Water exiting from the base of pot will not contain iron.
• Iron present as ferric (Fe3+) form which is insoluble in water and cannot be moved from its sites in the soil.
• Palaeosols that were in contact with an oxidising atmosphere when they formed will be oxidised and will be dominated by ferric (Fe3+) iron.
• Ferric iron is insoluble in water and so percolating fluids will not be able to transport it.
• Iron abundance in an oxidised soil profile should be reletively constant with depth.

Question 103

What do palaeosols tell us about atmospheric composition through time?

Answer 103

• When fossil soils from around the world are examined, a consistent picture emerges.
• All the well studied examples less than 1.9 Ga indicate highly oxidised conditions.
• Those older than 2.2 Ga reveal reducing conditions.
• Best explained by a sharp increase in atmospheric oxygen around 2 Ga.

Question 104

Outline the various isotopes of sulfur and briefly explain how they may be fractionated.

Answer 104

• Four naturally occuring isotopes ³²S (94.9%), ³³S (0.76%), ³⁴S (4.29%) and ³⁶S (0.02%).
• Mass dependent fractionation (MDF) controlled by mass difference and has specific rules (d³³S ~0.5 x d³⁴S ; d³⁶S ~2 x d³⁴S) and correlated relationships.
• Mass independent fractionation (MIF) has different controls and lost proportionally:
  
  • Causes: volcanic eruptions, gas phase reactions, photochemical oxidation
  • Cannot occur if even small amounts of oxygen present
  • Ozone layer must be absent
  • No significant atmospheric component in present day sulfur cycle.

Question 105

Describe how sulphur isotopes have revealed the oxidation state of the Earth’s atmosphere through geological time.

Answer 105

• Labratory studies show that:
• Prior to 2.45 Ga (Stage I), the oxygen content of the atmosphere was low enough (<10^-5 pal) to allow mass independent fractionation (MIF).
• Onset of oxidation occured in a period between 2.45 and 2 Ga (Stage II); “Great Oxidation Event; oxygen levels > 10-2 pal.
• Oxidation was complete after 2 Ga (Stage III); oxygenated atmosphere - no MIF.

Question 106

Using geological examples, describe the “Three Stages” of atmospheric oxygen change during Earth History.

Answer 106

• Evidence from the rock record point to an increase in atmospheric oxygen levels between 2.5 and about 2 Ga.
• A three-stage, “Three Box” summary model conveniently expresses the changes. The atmosphere, deep ocean and surface ocean form three distinct reservoirs for oxygen.
• Stage I, which persisted until about 2.5 Ga, all three reservoirs were anoxic. This is indicated by the absence of red beds and the preservation of detrital uranium minerals.
• Hydrothermal vents (‘black smokers’) delivered vast amounts of reduced ferrous iron into deep oceans.
• Local ‘oases’ in productive regions of ocean surface waters where photosynthesizing organisms flourished.
• The Earth would be steadily oxidized as atmospheric CH4 from methanogenic bacteria was photolytically
decomposed and H is lost to space.
• Initially, all the oxygen produced was mopped up immediately in oxidizing reduced gases exhaled by volcanoes.
• Stage II, between about 2.1 and 1.85 Ga, the atmosphere was oxidizing, but the oceans may have been stratified, with anoxic deep waters overlain by oxygenated surface waters.
• Both red beds and BIFS were widely deposited, indicating that the deep oceans were anoxic then, while the land surface was oxidising.
• Stage III, all three reservoirs were fully oxidizing, as in the modern Earth.

Question 107

Explain how oxygen levels can initiate evolutionary adaptations.

Answer 107

• More dissolved oxygen in water
  
  • Bigger marine organisms
  • Corals, foramifera, brachiopods
  • E.g. Carboniferous producids
  • Gigantoproductus 30 cm across
• Greater atmospheric density
  
  • Flapping is more efficient
  • Bigger flying insects e.g. Meganeura Monyi > 75 cm wing span
• Metabolism - bigger worms and insects respire by passive dissusion; spiracles and trachea; surface area limited: carboniferous cockroach 30 cm long
• Increased oxygen resulted in amphibian-reptile transition; the animal colonization of land.
  
  • Breathing loses water, more oxygen less water loss.
• Amphibian eggs have thin, permeable membrane while reptiles reproduce by amniotic egg. Amniotic egg has porous shell - more oxygen, fewer pores, stronger eggs.

Question 108

A system comprises interrelated components functioning as a complex whole, and defined by its boundaries.

Define an isolated system.

Answer 108

Boundaries prevents transfer of either energy or material.

Question 109

A system comprises interrelated components functioning as a complex whole, and defined by its boundaries.

Define a closed system.

Answer 109

Permits the exchange of energy but not material

Question 110

A system comprises interrelated components functioning as a complex whole, and defined by its boundaries.

Define an open system.

Answer 110

Permits the exchange of energy and material

Question 111

Explaining your reasoning state the type of system to which the Earth approximates.

Answer 111

• The Earth has a continuous supply of energy from the Sun.
• The Earth’s store of materials (excluding small amounts of extraterrestrial material) is finite.
• Overall Earth approximates a closed system.
• Since life on Earth began, the biologically important elements have been cycled, where elements are transformed from one chemical compound to another and pass through both the biosphere and geosphere.
• This process is termed biogeochemical cycling

Question 112

Explain what is meant by the terms “flux” and “residence time” and write a simple equation for calculating residence time.

Answer 112

• Flux is the rate of transfer of matter between reservoirs
• Residence time is the duration a given material/matter spends in a given reservoir

Residence time = amount in reservoir / flux

Question 113

State the subcycles of the carbon cycle and the relative time-scales on which they operate.

Answer 113

• Terrestrial carbon cycle
  
  • Short term
• Marine carbon cycle
  
  • Medium term
• Geological carbon cycle
  
  • Long term

Question 114

What is the commonly used unit for the carbon cycle?

Answer 114

10¹² kg C or “gigatonne”

Corresponds to 10¹⁵ g C or “petagram”

Question 115

Including reservoirs, fluxes and their appropriate values and units, draw a cycles diagram to represent the terrestrial carbon cycle.

Answer 115

values in 10¹² kg C and 10¹² kg C yr^-1

Question 116

Draw a cycles diagram to represent the marine carbon cycle, including reservoirs, fluxes and their appropriate values and units.

Answer 116

Remaining 0.2 x 10¹² kg yr^-1 is buried and becomes marine sediment

values in 10¹² kg C and 10¹² kg C yr^-1

Question 117

Including reservoirs, fluxes and their appropriate values and units, draw a cycles diagram to represent the geological carbon cycle.

Answer 117

values in 10¹² kg C and 10¹² kg C yr^-1

Question 118

What is the Biological Pump?

Answer 118

The combined biological processes which transfer organic matter and associated elements to depth.

It quickly removes carbon from surface ocean and atmosphere and puts it in the deep ocean.

Turning off the biological pump would lead to a 200ppm increase in atmospheric CO2 i.e. the biological pump locks away the equivalent of 200ppm of CO2 in organic carbon.

The bio pump in the modern ocean is not working at its full capacity. There are parts of the ocean that could have more life, and if these were utilized could increase its capacity by 50%.

Question 119

How does the organic carbon or soft tissue pump work?

Answer 119

1. Small algae called phytoplankton that live in the euphotic zone of surface ocean waters comsume CO₂ by photosynthesis and form organic matter as tissue (carbohydrate) and release oxygen. These tiny particles cannot sink and so cannot transport carbon deeper into the ocean.
2. Phytoplankton is at the bottom of the food chain and so are grazed upon by zooplankton. The excretion produced by zooplankton contains millions of phytoplankton and has now bio-accumulated (bio-packaged) into denser aggregate called marine snow. Marine snow is heavy/dense enough to start sinking.
3. As the aggregate sinks deeper into the ocean it gets acted upon by bacteria. Under the uptake of 1 mole of oxygen, the organic C is decomposed, freeing 1 mole of dissolved CO₂ (DIC) which is then physically mixed and recycled.
4. This carbon flux takes place in the ocean mixed layer (top 100m)

In modern oceans only 10% of DIC leaves this loop and only 1% of C_org gets deposited on the sea floor before respiration takes place, but there were times in Earth history when black shales were getting deposited e.g. anoxic events in Mesozoic

The amount of C_org getting deposited obviosly effects the climate balance and controls deep water ocean chemistry of O₂, inorganic carbon, and nutrients (the elements marine organisms need for life = C, N, P, Si, Cd, Fe etc.)

Question 120

Explain how the biological pump operates, and describe the nature and relative abundances of the materials involved.

Answer 120

• Surface organic matter decends
• During its passage to the deep ocean, marine organic matter decomposes in the water column, releasing CO2.
  
  • 90% recycled in surface waters
  • 9% recycled in deeper waters
• Around 1% of this organic matter reaches the sea-bed intact
• Once incorporated in the sediment, degredation continues - aerobic and anaerobic organisms
• 0.1% of the original surface water organic matter preserved. This small proportion of OM is an important leak in the system bc it allows carbon to enter the long term geological C cycle.

Question 121

Explain how the biological pump affects atmospheric composition

Answer 121

• If transport of photosynthetically produced organic matter to the deep ocean continued in isoloation, the surface waters would be stripped of dissolved CO2.
• Continuous exchange of gasses between the atmosphere and ocean causes CO2 in surface waters to be replenished.
• Activity of phytoplankton can, therefore, affect the composition of the atmosphere as well as the ocean.
• Overall, the effect of drawdown of CO2 from the atmosphere, the photosynthetic fixation of CO2 in surface waters, and the transport of the organic matter to deeper waters is the biological pump.

Question 122

Calculate the relative proportion of carbonate carbon to fossil organic carbon on Earth.

Answer 122

40 000 000 : 10 000 000

4 : 1

Question 123

State the annual terrestrial gross primary productivity (GPP).

Calculate the Net Primary Productivity (NPP) if ¾ of this was returned to the atmosphere as respired CO₂.

Describe what is likely to be the fate of this NPP carbon.

Answer 123

GPP = 120 x 10¹² kg C yr^-1

NPP = 120 x 10¹² - 90 x 10¹² = 30 x 10¹² kg C yr^-1

The likely fate of this NPP carbon is that it will be returned to the atmosphere as CO₂ following respiration by decomposers.

Question 124

What is the residence time of carbon in:

(i) Terrestrial plant biomass, and
(ii) Soil; and,

(iii) Comment on the relative fluxes and residence times. Explain any differences.

Answer 124

• i) The flux of carbon for land plants is 120 x 10¹² kg C yr-1; the amount in the reservoir is 560 x 10¹² kg C.
• Residence time = amount in reservoir / flux =
  560 x 10¹² kg C / 120 x 10¹² kg C yr^-1 = 4.6 yrs
• ii) The flux of carbon for soil is 60 x 10¹² kg C yr-1;
  the amount in the reservoir is 1500 x 10¹² kg C.
  Residence time = 1500 / 60 = 25 yrs
• iii) The fluxes in and out of terrestrial biomass are twice that for soil. The residence times for soil, however, are not 2 x soil.
• Carbon in soil has 5 x longer residence time. This is bc the soil reservoir is bigger than that for terrestrial biomass.

Question 125

If terrestrial biomass were spread evenly over the Earth’s surface (150 x 10⁶ km²), how much would there be per square metre?

Answer 125

560 x 10¹² kg / 150 x 10⁶ km²
= 3.7 x 10⁶ kg C per km²
= 3.7 kg C per m²

Although there is much heterogeneity, e.g. contrast tropical rainforest and deserts.

Question 126

What is the carbonate compensation depth (CCD)?

Answer 126

• In deeper water environments water is CO2-rich due to the decomposition of organic matter.
• CO2 is more soluble in water at lower T’s and higher P’s.
• The lower T’s and higher P’s in deep ocean waters will allow them to hold more dissolved CO2 than surface waters.
• CO2 dissolved in water forms carbonic acid; water will be corrosive to CaCO3.
• Level at which the rate of dissolution of CaCO3 is equal to the flux of material through the water column is called the CCD.
• Below this depth, all shells dissolve.
• It is for this reason that the deep ocean floor has no CaCO3 sediments.

Question 127

If, due to fossil fuel use, atmospheric CO2 levels continue to rise, how do you think this will affect the carbonate compensation depth (CCD)?

Answer 127

• Increased CO2 conc.s in the atmosphere would lead to a corresponding increase of dissolved CO2 in the ocean.
• Bc dissolved CO2 forms an acidic solution, the average acidity of the ocean would increase and the CCD would shift to a shallower level.

Question 128

If the marine biological pump suddenly began to transport twice as much organic debris to the ocean floor, much of which became incorporated into sediments and ultimetly rock, would atmospheric oxygen levels increase or decrease?

Answer 128

• Atmospheric oxygen levels would increase.
• For each carbon atom that enters the rock reservoir, one oxygen molecule is left behind in the atmosphere.

Question 129

Explain the process of nitrification.

Answer 129

• Nitrification is the production of nitrate.
• Most soils are acidic (mineralization usually leads to high levels of NH₄⁺)
• In well oxygenated soils, nitrifying bacteria oxidise the NH₄⁺ to NO₂^- and NO₃^- (releasing energy in the process)
• Nitrification takes place in two sequential reactions involving bacteria (Genus Nitrosomonas and Genus Nitrobacter)

2NH₄⁺ + 3O₂ = 2NO₂^- + 2H₂O + 4H⁺
2NO₂^- + O₂ = 2NO₃^-

• Produces soluble, mobile, oxidising agent - nitrate - during thunderstorms and at vents as well as in oxic environments
• NO₃^- can be leached from soils and may move to organic-rich reducing environments (denitrification)

Question 130

Explain the process of denitrification.

Answer 130

• NO₃^- is converted back to nitrogen gas
• With, minor amounts of N₂O and NO
• Process performed primarily by heterotrophic bacteria (e.g. Paracoccus denitrificans or various pseudomonads)
• Occurs in organic-rich anoxic environments
• Denitrifying bacteria use NO₃^- instead of O₂ during the oxidation of organic matter in reducing environments
• Converts fixed N to atmospheric N2 - these loses balanced by N fixation

Question 131

With the aid of a figure describe a soil profile that is in contact with the atmosphere and indicate how the process of denitrification and nitrification are connected.

Answer 131

• Nitrification-denitrification cycle
• Soil well aerated at surface
• Shallow organic N converted to nitrate
• Much leached from the soil
• At depth, soil waterlogged and anoxic
• Nitrate washed in from above
• Denitifying bacteria e.g. Pseudomonas
• Oxidize the organic matter using nitrate instead of oxygen
• End products are N₂, N₂O and NO

Question 132

Define what is meant by digestion and detail the chemical steps that occur for nitrogen containing materials

Answer 132

• Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a bloodstream
• Peptide bonds of that link the amino acids of the injested proteins together are broken and individual amino acids are released.
• Some amino acids are used to make proteins and repair damaged tissues, and excess protein is an energy source.
• During mineralization, amino groups are removed and the carbon skeletons are catabolized to CO₂ and water.
• Then, nitrogen is released initially as NH₃, this molecule is rapidly converted to NH₄⁺.
• NH₄⁺ can be toxic and its removal requires water.
• Aquatic organisms dissolve it away, and most mammals (including humans) convert it to urea, CO(NH₂)₂.
• Birds, reptiles and insects produce insoluble uric acid C₅H₄N₄O₃ (guano, fertilizer)

Question 133

Animals eat plant protein and excrete the waste nitrogen in the form of urea. This lies on, or close to the surface soil.

What happens to the urea?

Answer 133

• Decomposes to NH₃ and CO₂
• CO(NH₂)₂ + H2O → 2NH₃ + CO₂
• NH₃ lost to atmosphere
• Process may be very common on arable land
• Manures and animal slurries can lose up to half of their nitrogen by ammonia volitization

Question 134

State what is meant by the term “nitrogen fixation”

Answer 134

• Fixation is the first step in the nitrogen cycle
• For use in growth N must be “fixed” or combined:
  
  • Ammonium (NH4+) ions
  • Nitrate (NO3-) ions
  • Urea [CO(NH₂)₂]
• Plants secture their N in fixed form through assimilation.

Question 135

Explain why nitrogen fixation is difficult.

Answer 135

Even though there is abundant N in Earth’s atmosphere, nearly 79% is in the form of N2 gas.

N2 is unavailable for use bc of strong triple bond making the molecule almost inert.

N is often the limiting factor for growth.

Question 136

Explain why N is often the limiting factor for growth.

Answer 136

• N is difficult to fix, but
• Plants must secure their N in “fixed” form through assimilation.
• Animals secure their N compounds from plants (or animals that have fed on plants)
• Weathering of rocks is slow (negligible effect on the availability of fixed N)

Question 137

Give non-biological and biological examples of nitrogen fixation.

Answer 137

• Small amount of ammonia is produced by lightning.
• Small amounts at volcanic vents (conventional thought)
• Ammonia also produced industrially by the Haber-Bosch process
• Major conversion of N₂ into ammonia achived by microorganisms (biological fixation x2 non-biological)

Question 138

Describe nitrogen fixation by lightning

Answer 138

• Lightning produces 1,000-100,000 Amps and reaches 30,000°C in its less-than-half-a-second duration.
• Produces more energy than all of the electrical utilities in the world combined during that instant.
• Splits triple bond in N₂ (N₂ + O₂ → 2NO) and N is rained out in nitric acid.
• 10 x 10¹² g yr^-1 fixed N.
• Important prebiotic source of fixed N.

Question 139

Describe N fixation by vents

Answer 139

• Volcanic vents promote the thermal fixation of atmospheric N₂.
  
  • At Masaya volcano, Nicaragua, NO and NO₂ are present in volcanic aerosols
  • NO_x levels are an order of magnitude above background.
  • HNO₃ contents are elevated.
• Present-day global production of fixed N at hot vents = 14 x 10¹⁰ g yr^-1
• Potentially important source of fixed N on the early Earth

Question 140

What is the prebiotic relevance of N fixation by vents

Answer 140

• Conversion efficiency would have been lower in a non-oxygenated atmosphere
• More subaerial volcanism

Question 141

Why was fixation by vents a potentially important source of fixed N on the early Earth?

Answer 141

• 1.4 x 10¹² g yr^-1 of fixed N during major episodes of volcanism
• Comparable to nitrogen-fixation rates from lightning

Question 142

Describe N-fixation by microbes

Answer 142

• Ability to fix N is found only in certain bacteria
• Some N-fixing bacteria live free in the soil
• Some live in a symbiotic relationship with plants of the legume family (e.g. soyabeans, alfalfa)
• Some establish symbiotic relationships with plants other than legumes (e.g. alders)
• N-fixing cyanobacteria are essentially for fertility of semi-aquatic environments, e.g. rice paddies
• Biological N-fixation requires a complex set of enzymes and a huge expenditure of energy.
• First stable product of the process is ammonia (NH₃), this is quickly incorporated into proteins and other organic nitrogen compounds.

Question 143

What’s a symbiotic relationship?

Answer 143

A close association between two distinct species where both organisms benefit from the relationship

Question 144

Give an example of biological N-fixation in nature.

Answer 144

• Every plant in the Lower Sonoran desert in Arizona depends on biological N fixation.
• Free-living cyanobacteria associate with lichens.
• Contribute N to the soil by forming a cryptobiotic crust (delicate, thin, fibrous, biological soil crust)
• Leguminous plants followed (N-fixing Rhizobium in their root nodules)
• E.g. Parkinsonia sp.

Question 145

Describe industrial N-fixation.

Answer 145

• Haber-Bosch process
• Hydrogen is first obtained from natural gas (methane)
  
  • Ni catalyst
  • 30 atmospheres
  • 750°C
  • CH₄ + 2H₂O → CO₂ + 4H₂
• Nitrogen and hydrogen are then reacted to produce ammonia
  
  • Iron catalyst
  • 200 atm
  • 450°C
  • N₂(g) + 3H₂(g) ⇔ 2NH₃(g) + heat

Question 146

Why were Fritz Haber and Carl Bosch named the most influential persons of the 20th century according to Nature in 1999?

Answer 146

• Haber-Bosch products represent fertilizers from non-natural sources (agriculturally significant)
• Considered the most important invention of the 20th Century bc it initiated population explosion (1.6 billion in 1900 to 6.0 billion in 2000)
• 1% of the world’s present-day energy supply is used for Haber-Bosch process, producing 500 million tons of artificial fertilizer per year.
• This sustains roughly 40% of the population!!

Question 147

What is ozone and where is it located in our atmosphere?

Answer 147

• Ozone (O₃) is a highly reactive and toxic gas located in the very stable stratosphere.
• Most (~90%) of ozone is in the stratosphere between 10-16 km up to ~50 km altitude.
• Most ozone resides in an “ozone layer” 15 - 30 km altitude.
• The remaining ozone (~10%) resides in the troposphere, the lowest region of the atmosphere.

Question 148

Explain how how ozone levels are remotely measured.

Answer 148

• Measure amount in a column of atmosphere directly above a point at Earth’s surface.
• Measured using a Dobson spectrometer.
• Expressed in Dobson units (DU).
• Ozone absorbs UV light but does not absorb visible light.
• Amount of ozone in the atmosphere determined by measuring the difference between the two wavelengths.

Question 149

Explain how how ozone levels are directly measured.

Answer 149

• Detected by aircraft and satellites in contact with ozone
• UV absorption
• Electrical currents generated by chemical reactions involving ozone.
• Small balloons or aircraft travel to required locations, transporting measuring devices (ozonesondes)

Question 150

Explain how ozone is produced in the stratosphere.

Answer 150

• Sidney Chapman deduced reactions for production and destruction of atmospheric ozone.
• Ozone production begins when an O₂ molecule is broken apart by light (hv)
• UV radiation with wavelenghts < 240 nm
• Process termed photodissociation.

O₂ + hv → 2O

• O atom combine with another O₂ molecule to produce ozone (note: lifetime of O very short in the stratosphere, typically < 1 s)

O + O₂ → O₃

• Amount of energy generated by the collision is too much for the newly formed ozone molecule, so
• A helper molecule, M, which can be any other atmospheric gas removes excess.

O + O₂ + M → O₃ + M

Question 151

Explain how ozone is broken in the stratosphere.

Answer 151

• Ozone is a strong absorber of light between 240 and 310 nm (energy absorbed and released as heat).

O₃ + hv → heat

• However, with wavelengths above 310 nm, ozone is dissociated to an oxygen atom and molecular oxygen.
• This reduction also gives out heat.

O₃ + hv → O + O₂

• We are now back to the raw materials of ozone generation.

O + O₂ → O₃

Question 152

Using a simple diagram, describe the Chapman cycle of reactions reactions and state the consequences of this cycle for the stability of stratospheric ozone levels.

Answer 152

• Chapman realized photochemical production and destruction of ozone is a cyclic process.
• Cycle stops when a fourth reaction occurs.
• Ozone molecule meets single atom of oxygen
• Two stable molecules of O2 are formed
• Overall, natural ozone loss should balance production.

Question 153

Describe how ozone depletion and its main causes were recognized.

Answer 153

• Stratospheric (“good”) ozone absorbs UV-B radiation from the Sun.
• Therefore, there is a negative correlation between the two factors: high amounts of UV-B at the surface = low amounts of stratospheric ozone and v.v.
• In the 1970’s numerical models and lab. experiments discovered 30% less ozone in the stratosphere than predicted.
• Depleted by increased rate of ozone destruction:
• Raised conc.s of ozone-depleting molecules in the stratosphere.
• Ozone-depleting molecules (X) disturb the ozone cycle.
• Net change is a loss of ozone.

Question 154

By providing generic reactions equations, outline the mechanism for ozone depletion,

Answer 154

X + O₃ → XO + O₂

XO + O → X + O₂

Net change:
O + O₃ → 2O₂

• X is not included in the net reaction bc it is a catalyst
• Trace amounts of X can remove large quantities of ozone bc it is continually recycled

Question 155

Define catalyst

Answer 155

A substance which increases the rate of reaction but remains unchanged at the end

Question 156

Give 3 examples of ozone depleting molecules and their sources.

Answer 156

• NO ; major source = supersonic jet aircraft
• CFC’s e.g. CFCl₃ (Freon-11) ; refrigerant, propellant
• BFC’s e.g. CF₃Br (Halon-1301) ; fire extinguisher

Question 157

What are the sources of NO?

Answer 157

• Indirectly from biological N2O
• Accelerated by the application of agricultural fertilizers
• Directly from supersonic aircraft

Question 158

How do CFC’s and BFC’s affect ozone?

Answer 158

• CFC’s reach the stratosphere and decompose to release chlorine radicals that catalytically destroy ozone
• BFC’s have similar effect

Question 159

What are the 3 key obserations that gave clues as to the origin of the ozone hole?

Answer 159

1. The ozone hole is largely an Antarctic phenomenon.
2. The ozone hole occurs only during October.
3. The ozone hole did not exist prior to 1967.

Question 160

Why is the ozone hole largely an Antarctic phenomenon?

Answer 160

• Stratosphere is relatively isolated from adjacent areas during the winter months
• Cold, dense air sinks in a polar vortex
• Wind speeds are much higher than the surrounding atmosphere
• Transfer of gas into the Antarctic stratosphere is very limited
• Any ozone depletion which occurs cannot be replenished from other parts of the Earth’s stratosphere

Question 161

Why does the ozone hole only occur during October?

Answer 161

• Very low T’s during May to September
• Clouds generally confined to the troposphere
• Stratosphere over Antarctica is so cold (less than 80°C ???) that small amounts of nitric acid and water freeze out.
• Reactions occur that involve molecules in both the gas phase and solid phase.
• They are termed heterogeneous reactions.

Question 162

Explain the heterogeneous reactions that cause depletion of ozone over Antarctica in October.

Answer 162

• In the stratosphere chlorine and nitrogen containing molecules combine to form a reletively unreactive compound - Chlorine nitrate or ClONO₂.
• ClONO₂ does not react easily with ozone or oxygen, but forms an inert store of Cl and NO.
• For this reason, it is often termed a “reservoir compound”.
• On surfaces of polar stratospheric particles, however, heterogeneous reactions can release chlorine.
• ClONO₂ and HCl react on the surfaces of the ice particles, leading to the production of Cl₂.
• Cl₂ itself will not destroy ozone, but conversion of Cl₂ to Cl radicals determines the timing of ozone hole.
• Cl₂ remains frozen in the stratospheric particles until the Antarctic spring in October.
• Levels of sunlight increase and the Cl₂ is released and photodissociated to form chlorine radicals.
• They begin a catalytic cycle of ozone destruction.

Question 163

Why did the ozone hole not exist prior to 1976?

Answer 163

Cl has anthropogenic origin, hence 1976 origin of ozone hole.

Question 164

Describe the relationship between oxygen levels and ozone production and state when the Earth is likely to have (first) developed a significant ozone layer.

Answer 164

• Ozone is derived from atmospheric oxygen, and oxygen built up around 2 Ga during the Great Oxidation Event.
• Only small amount of oxygen needed
• Ozone production has non-linear relationship with oxygen conc.
• Photochemical models suggest 100 DU at 0.001 PAL
• Decent Ozone layer present at 2.3 Ga

Question 165

Give a geological example of where ozone depletion seems to have affected the Earth’s biosphere.

Give fossil evidence.

Answer 165

• The Fungal spike (fungal event)
• Unique abundances of fungi
• Coincident with isotope shift
• End-Permian bioevent
• Worldwide
• All environments
• Destruction of terrestrial biomass (gymnosperm forests)
• Replaced by opportunistic herbs (e.g. 1-2 m tall Pleuromia - a spore producing lycopod)
• Fossil evidence in early Triassic Red Sandstone of the Eifel area, Germany.

Question 166

Describe any additional plant evidence that reveals the atmospheric cause of a Fungal Spike

Answer 166

• Modern day example is the contaminated area of the Black Triangle, Great Mountains.
• Boundary between Germany, Poland, Czech Republic.
• Where buring of black coal (sulfur-rich lignite) led to the release of sulfur dioxide (SO₂) and nitrogen dioxide (NO₂) led to the production of acid rain (nitric acid).
• Between 1972 and 1989, 50% of coniferous forest died (50% of children born also died).
• Deforestation led to opportunistic expansion of lower vascular plants and proliferation of fungi.
• Extinction = loss in diversity = dominated by opportunistic herbs / decomposers dominant over others that don’t survive in low pH conditions.

Question 167

Suggest a geological mechanism for the End-Permian Fungal Spike occurrence.

Answer 167

• The morphology of End-Permian lycopsid microspores tell us something of the possible mechanism.
• Tetrads normally seperate following dispersal,
• However, during the E.P., tetrads dispersed intact, with no seperation - and this occured worldwide.
• It is seen that the prevention of tetrad pectin (plastic) degredation caused by gene mutation from radiation damage was the cause.
• But what was the source of radiation? Cosmic radiation, or depletion of ozone in some way? See next card…

Question 168

During the Late Permian Fungal Spike, what was the source of radiation that caused gene mutation in lycopsid microspores (tetrads)?

Answer 168

• Cosmic radiation could be a good source, but only lasts 10-100s years - too short for the End-Permian.
• Maybe an impact could have destroyed the ozone layer by punching a hole through it?
  
  • Helium and osmium show terrestrial values.
  • No conclusive evidence for impact (e.g. no shocked quartz)
• Siberian traps viable option, the largest Phanerozoic volcanic event, associated with massive emissions and aerosol release and acidification..
• Hydrothermalism (heat + water) of halogen-rich country rocks (evaporitic sed. basin) (organohalogens) over 500 kyrs, leading to ozone depletion and UV-B increase and gene damage.
• Followed by ecosystem destabalization, loss of rooted vegetation and soil erosion.
• Affected carbon cycle.

Question 169

Describe a recently developed biological proxy for ozone levels.

Answer 169

• UV-B radiation (280-315 nm) damages plant proteins, membrane lipids DNA and can cause mutations.
• But as plants need sunlight for photosynthesis, they face a trade-off between UV-B exposure and the need for photosynthesis.
• One way around this imbalance is the use of UV-B absorbing compounds:
• Sporopollenin, structural contituents of outer walls of pollen and spores from vascular plants.
• Aromatic acids absorb in the UV-B range.
• Aromatic acids - UV pigment abundance proxy UVB flux.
• Results show that ozone has been decreasing with time since ~1960 at high latitudes.

Question 170

Describe the multiplication rules that help define positive and negative feedback loops

Question 171

A newly discovered planet called “Carbonica” is very similar to the Hadean Earth with few land masses evident and the prolific production of submarine carbonated basalts. On Carbonica the amount of global carbon is 1 x 10²⁰ kg, sea floor lifetime is 60 million years and complete circulation of the ocean (and the atmosphere with which it readily exchanges) through hydrothermal vents occurs in 10 million years.

Describe, qualitatively, how carbon was distributed between the atmosphere, ocean and land on Carbonica.

Answer 171

• Small continents result in little silicate weathering and small land storage, small carbonate stores.
• Atmosphere, ocean and sea floor primary reservoirs.
• More dissolved inorganic C (in atmos. + ocean) during the Hadean, with higher heat flux and ideal conditions for forming carbonated basalts (carbonites) (water pumped through vents).
• Interaction between ocean and atmosphere so regular that they have an equal proportion of carbon.
• Assuming no land storage:
• Carbon 6:1 - seafloor:ocean,
• T.f. 1/7 (15%) present in atmosphere and ocean, relative to sediments.

Question 172

A newly discovered planet called “Carbonica” is very similar to the Hadean Earth with few land masses evident and the prolific production of submarine carbonated basalts. On Carbonica the amount of global carbon is 1 x 10²⁰ kg, sea floor lifetime is 60 million years and complete circulation of the ocean (and the atmosphere with which it readily exchanges) through hydrothermal vents occurs in 10 million years.

Explaining your reasoning, calculate the amount of carbon resident in the sea floor sediments and the ocean and atmosphere of Carbonica.

Answer 172

• Taking simple C cycle assumptions:
• Assume no continents so no land storage.
• Atmosphere, ocean and sea floor only reservoirs.
• Assume 100% efficiency for carbon removal in vents.
• Seafloor lifetime 60 Myrs; ocean through vents in 10 Myrs
• 10²⁰ kg surface carbonate 4.5 Ga (assume same as today)
• Carbon 6:1 - seafloor:ocean
• 1/7 (15%) present in atmosphere + ocean
• 0.15 x 10²⁰ kg = 1.5 x10¹⁹ kg
• C_atmos = C_ocean = 7.5 x10¹⁸ kg (1.5 x10¹⁹ / 2)
• C_sea.sed = 0.85 x 10²⁰ = 8.5 x10¹⁸ kg

Question 173

A newly discovered planet called “Carbonica” is very similar to the Hadean Earth with few land masses evident and the prolific production of submarine carbonated basalts. On Carbonica the amount of global carbon is 1 x 10²⁰ kg, sea floor lifetime is 60 million years and complete circulation of the ocean (and the atmosphere with which it readily exchanges) through hydrothermal vents occurs in 10 million years.

How does the amount of carbon in the ocean/atmosphere of Carbonica compare with the estimated 4.1 x 10¹⁶ kg of the present day Earth? What effects would this have?

Answer 173

Carbonica

• Carbon 6:1 - seafloor:ocean
• 1/7 (15%) present in atmosphere + ocean
• 0.15 x 10²⁰ kg = 1.5 x10¹⁹ kg
• Catmos = Cocean = 7.5 x10¹⁸ kg (1.5 x10¹⁹ / 2)
• Csea.sed = 0.85 x 10²⁰ = 8.5 x10¹⁸ kg

Present-day Earth

• 4 x10¹⁶ + 7.6 x10¹⁴ (ocean + atmosphere)
• 4.076 x10¹⁶ kg = 4.1 x10¹⁶
• Carbonica(/Hadean) has ~400 (365.9) times more CO₂
• The effect = substantial greenhouse effect

Question 174

Using appropriate equations, describe how organic matter is produced and utilised in the biosphere.

(State how this process relates to oxygen levels in the atmosphere. Explain the role of nutrient-related feedback mechanisms in controlling the production of organic matter and the level of atmospheric oxygen.) ?

Answer 174

• Photosynthesis
  
  • light + nCO₂ + nH₂O → (CH₂O)n + nO₂
  • Light is harvested and converted to energy stores
• Respiration
  
  • (CH₂O)n + nO₂ → nCO₂ + nH₂O + energy
  • Energy store is consumed to drive biochemical reactions
• Balanced equations = only energy is consumed

Question 175

Why will the carbon atoms contained in CH4 continue to take part in greenhouse warming after the CH4 has been destroyed by oxidation?

Answer 175

no answer in notes