UNIVERSITY OF EAST ANGLIA
School of Environmental Sciences
Main Series PG Examination 2014-2015
EARTH AND LIFE
ENV-MA38
Time allowed: 2 hours
Answer ONE question from Section A and ONE question from Section B.
Write EACH ANSWER in a SEPARATE booklet.
The maximum number of marks available for your answers in SECTION A is 100 marks
The maximum number of marks available for your answer in SECTION B is 100 marks
The TOTAL number of marks available for the paper is 200
The ENV data book will be provided
A separate sheet for question 4 a) answer is provided
Notes are not permitted in this examination
Do not turn over until you are told to do so by the Invigilator
ENV-MA38
Copyright of the University of East Anglia
Module Contact: Dr Martin Johnson, ENV
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SECTION A: ESSAY QUESTION
Answer ONE question
[100 marks]
1. Describe the major features of the carbonate-silicate feedback cycle on atmospheric CO2
concentrations.
Your answer should address the timescales that the feedback works over, and how the
evolution of land plants in the Phanerozoic affected the cycle. Discuss the implications of
this feedback mechanism on likely atmospheric CO2 concentrations on the early Earth.
Does the evidence agree?
2. What role have orbital parameters played on Quaternary change?
Your answer should focus on the recent 100 kyr glacial cycles and cover the role of
different orbital changes and what their effects are on surface energy and glacialinterglacial transitions.
3. When did life start on the Earth, and what does this imply for the prospects of life existing
elsewhere in the universe?
Your answer should evaluate the evidence for when the Earth became habitable and
evidence for early life. Explain the contrasting conclusions that can be drawn from what we
know about life on Earth about the likelihood of simple life evolving elsewhere in the
universe. What implications can be drawn about the likelihood of the evolution of intelligent
life?
END OF SECTION A
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SECTION B: STRUCTURED QUESTION
Answer ONE question
[100 marks]
4. Archean Metabolism and Modern Analogues
a) The following table describes a series of key microbial metabolisms common in the
Archean Eon. Complete this table on the separate sheet provided and attach to the answer
booklet.
Metabolism
Energy source
Carbon
source
Anoxygenic
photosynthesis
_____________
_______
Electron
donor
Characteristic Equation
e.g. Fe2+, H2S
e.g. CO2 + 2H2S + hv ->
_________________________
Methanogenesis
Reduction of CO2
CO2
e.g. H2S
___________________ ->
CH4 + 2H2O
Methanogenic
fermentation
Disproportionation
of organic matter
Organic
matter
N/A
Oxygenic
photosynthesis
______________
_______
_________
Methanotrophy
(aerobic)
______________
CH4
2CH2O -> __________
____________________
N/A
____________________
[20]
b) In what order is it likely that the organisms listed above evolved and why?
[10]
c) Banded iron formations (BIFs) are common throughout the Archean and have been
claimed as evidence of oxygenic photosynthesis. More recently other biotic processes have
been proposed as causes of BIFs. In this section, the questions can be answered with or
without the use chemical equations.
i)
ii)
Describe a mechanism of banded iron formation that is consistent with oxygenic
photosynthesis.
Describe a mechanism of banded iron formation that is consistent with
anoxygenic photosynthesis.
[25]
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d) Prior to the great oxidation event it is thought that oxygenic photosynthesis and
methanogenic fermentation were the dominant metabolic pathways controlling atmospheric
oxygen.
i)
ii)
What is the net result of these two metabolisms acting together?
Explain why this net metabolism leads to the permanent oxygenation of the Earth
system.
[25]
e) Briefly describe a natural present-day microbial system that is driven by coupled
methanotrophy and chemolithoautotrophy. How is it likely to differ to the pre-photosynthetic
microbial systems on the early Earth?
[20]
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5. Gaia and Daisyworld
The Gaia hypothesis, as originally defined, postulates ‘atmospheric homeostasis by and for
the biosphere’.
a) On reading about this hypothesis from afar, alien Professor Snikwad is not impressed.
He is convinced that life cannot be regulating the composition of any planet’s atmosphere.
Give three arguments to support his view.
[20]
b) Extraterrestrial scientist Dr Kcolevol is determined to prove Professor Snikwad wrong.
With the help of his student Nostaw Werdna, he sets about seeding a bare planet with two
types of life; black and white daisies. The black daisies warm their surroundings and the
white daisies cool their surroundings. Both types of daisy start growing at 5oC, they grow
best at 22.5oC and stop growing at 40oC. The figure below shows how temperature on this
planet would change in the absence of life, as the luminosity of the parent star steadily
increases:
i)
Describe, with the aid of diagrams where appropriate, how the two types of
daisies interact with each other and with planetary temperature to regulate
their environment.
ii)
In your answer book, copy the above figure and sketch what happens to the
temperature when the world is seeded with the two types of daisy (and again,
the luminosity steadily increases).
iii)
Draw a separate plot of how the corresponding black and white daisy
populations change with time.
iv)
Sketch what happens to the temperature and daisy populations if the
luminosity is steadily reduced from a high value.
[50]
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c) Daisyworld is an idealized model system demonstrating the potential for planetary-scale
regulation of conditions by organisms subject to natural selection. Give an example of a
potentially climate-regulating negative feedback on Earth driven by living organisms and
their interaction with the environment, and describe the mechanism by which it works.
[15]
d) Discuss the testability of the Gaia hypothesis and what this means for its usefulness as
a framework for exploring the Earth system.
[15]
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6. Energy Balance Models and Snowball Earth
a) In your answer book, sketch a feedback diagram for the ice-albedo feedback, linking
“solar luminosity”, “absorption of sunlight”, “global mean temperature” and “ice/snow cover”.
Indicate if each interaction is positive or negative, and if the overall feedback is positive or
negative.
[15]
In the rest of the sections of this question please show your working in the answer
book
b) Budyko’s simple energy balance climate model for the Earth balances incoming and
reflected sunlight with emitted shortwave radiation to compute Earth’s effective temperature
Te (in K):
T4e =
Where S is the incoming solar energy (in W m-2) of which fraction A (the planetary albedo)
is reflected and σ is Stefan’s constant (σ = 5.67 x 10-8 W m-2 K4). For the present-day Earth,
S=1365 W m-2 and the planetary albedo is 0.3 (no units).
Earth’s global mean surface temperature (Ts) depends on the effective temperature and the
atmospheric greenhouse effect. For a CO2/H2O atmosphere, we can use:
Ts = Te [1.1265 + 0.017 ln(C)]
Where ln(C) is the natural logarithm of the atmospheric concentration (CO2). C is in units of
PIL (pre-industrial level), where 280 ppm = 1 PIL (so if the CO2 concentration is 560 ppm,
C=2).
i) Compute the global mean temperature expected for doubling of pre-industrial CO2
concentrations
ii) What is the climate sensitivity according to this model? How does this compare to
modern estimates?
[20]
c) Six hundred Myr ago, the Sun emitted only 94% of its current energy. During this time
period (the Neoproterozoic), it is postulated that the Earth underwent a series of “Snowball
Earth” events, where the ice-albedo feedback contributed to the complete glaciation of the
planet.
i) Assuming that CO2 concentration and albedo were the same in the Neoproterozoic
as their pre-industrial values, what was the global mean surface temperature 600
Myr ago?
ii) What Neoproterozoic CO2 concentration would be necessary to trigger run-away
ice-albedo feedback resulting in snowball conditions?
iii) After passing the tipping point for run-away ice-albedo feedback, Earth quickly
becomes completely glaciated, ending up with a planetary albedo of 0.65. What is
the global mean surface temperature for this Neoproterozoic glaciated state?
[25]
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d) In order to trigger deglaciation from a snowball state, global climate models predict that
a global mean surface temperature of 260 K is required.
i) What occurs when the temperature reaches 260 K and how does this trigger
deglaciation?
ii) What CO2 concentration would this require on a Neoproterozoic snowball Earth?
iii) What mechanism causes the rise of atmospheric CO2 and the ultimate escape
from snowball conditions?
iv) What would be the global mean surface temperature immediately after all the ice
had melted? What other feedback mechanism would become important at this point?
[25]
e) What evidence is there in support of deep/complete glaciations and their after-effects
during the Neoproterozoic?
[15]
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