ES1006 Astrobiology
-EXPLORING THE INTERFACE BETWEEN
MICROBIOLOGY AND THE ROCK RECORDASSESSED OPEN BOOK COURSEWORK 25 %
Deadline 10th March, 12PM
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Astrobiologists searching for evidence of past, extinct microbial life on other worlds, like
Mars, have to do so using data collected from instruments on board surface rovers, and
orbiting spacecraft. Interpretation of these datasets is rooted in our understanding of
microbial life on Earth. Visual datasets from rover cameras enable scientists to conduct
‘field geology’ on another planet, including identifying evidence of past habitable
environments revealed by the rock record. Analytical datasets revealing the chemistry of
planetary materials can reveal whether or not they contain evidence of microbial life.
This module involves a signficant amount of independent study. This piece of
coursework has been allocated an upper estimate of 48 hours of work. Do not leave this
coursework to the last minute! You will not be able to rush this. You have 4 teaching
weeks plus the February vacaction to complete this assessment – use this time wisely!
Instructions and Guidelines:
This assessment comprises three parts. For the first, you will investigate data from living
microbial mats. The second part will take you on a series of virtual field trips to Western
Australia, which hosts some of the most iconic rock formations of the Archean Earth that
preserve microbial mat fossils. The field trips were compiled by researchers at Arizona
State University and feature several world-leading experts in Archean geology and
geobiology. Insights gained from the rock units that you will get to see have laid the
foundation of how we explore the geology of Mars today. The third part will see you use
your knowledge gained from parts one and two to critically assess some much-debated
research claiming to identify (a) evidence of some of the earliest microbial life on Earth,
and (b) evidence of microbial life in a Martian meteorite, and discuss the broader
implications for finding evidence of life (or not!) on Mars.
PART 1 – Living microbial mats in the laboratory
On Earth, many microorganisms in microbial mats produce or consume oxygen. Oxygen
is produced by photosynthesis and is consumed by respiration. By measuring the
concentration of oxygen within a microbial mat, it is possible to see what the net balance
of photosynthesis and respiration is. By also measuring oxygen concentration at various
depths, it is possible to see what the net balance is at each of these depths. A set of
measurements of oxygen vs. depth is called an oxygen concentration profile.
The Excel spreadsheet “Coursework DATA” on Moodle contains oxygen depth profile
data from microbial mats being incubated at NASA Ames Research Center. A robotic
probe was used to make one profile of oxygen concentration down through the centre of
each of 18 individual mats. The 18 mats are arranged into 6 boxes, each of which contains
3 mats. The boxes are subjected to three different experimental treatments involving
different combinations of salinity and sulfate concentration.
1. Using the ‘Analysis’ tab in the excel spreadsheet, calculate the average (avg) for the
three different treatments in the Calculations Table in column AM in the spreadsheet.
Copy and paste your Calculations table below by selecting the cells for your Calculations
table, copying, and pasting it as a ‘Picture’ below using Paste Options.
2. Using the ‘chart’ function in Excel, use your data in the Calculations table to create
an XY scatter plot of the average oxygen concentration versus depth for the mats in
each of the three treatments.
3. The independent variable is the variable that you change on purpose to investigate
the effect on the dependent variable. What is the independent variable for this study?
Using your plot, answer the following short answer (i.e. 1-3 sentences) questions:
4. At what depth are the mats in each treatment producing the most oxygen?
5. At what depth could microbial sulfate reduction be occurring and why?
6. Which treatment produces the most oxygen and why?
7. Study the figure below of a cross-section through a living microbial mat, and its
corresponding O2 depth profile. Indicate on the O2 profile the point at which the
microbial community within the mat must be anaerobic, and explain why.
8. Below is another depth profile of the same microbial mat cross-section, this time for
hydrogen sulphide (H2S). Why does H2S increase as we go deeper into the microbial
mat?
9. Below is another depth profile of O2, but this time the mat has experienced a period
of darkness. Explain the difference in the O2 depth profile between this plot and the
one in question 7.
10. On the early Earth, before cyanobacteria evolved, which microbial groups in the
microbial mat above would have been prevalent?
11. Go to https://1000springs.org.nz/. This is an online database of microbial
communities living within hot springs in the New Zealand geothermal areas. Go to ‘Our
Science’  ‘Data Overview’ and use the interactive plot to select a hot spring of your
choice. Note, the colour grading relates to ‘Chemical Comparison’ and the default is set
to ‘Sulfate’, but you can change this if you like.
For your selected site, describe (i) the spring’s physicochemical characteristics, (ii) the
chemistry of the environment, and (iii) one of the more abundant members of the
resident microbial community (use Google search to find out more about the taxon
selected).
How does this hot spring and its microorganisms compare to the ones studied in the
laboratory microbial mats from the NASA Ames Research Centre you analysed?
PART 2 – Living and fossil microbial mats in the field
To access the field trips, go to the following website:
https://vft.asu.edu/
You will find a series of virtual field trips listed along the bottom of the page. Work
through the field trips listed below, in any order you wish. Each fieldtrip will take you
approximately 1.5 hours, but you can do them from the comfort of your own sofa, and at
your own pace.
• Living Microorganisms
• Knossos Locality
• Dresser Formation
(1) Use the table below to make notes and labelled sketches as you conduct the virtual
fieldtrip
Sketches could be of features of interest seen in the rocks. Include an approximate scale.
Notes can be of features pointed out in the video demos, as well as features you see in the
high resolution photos.
Field site
Living
Microorganisms
Knossos
Observations and sketches
Interpretations and notes
Dresser
2) Go to the NASA Perseverance rover webpage (https://mars.nasa.gov/mars2020/)
and choose 3 instruments on board Percy you would choose to investigate the rocks at
either Knossos or Dresser. Justify your choices and explain what each instrument would
tell you [Approx. 100-150 words].
PART 3 – Contentious microbial fossils in the geological record
An important life skill is to be able to condense complicated information into a simple
format. Regardless of your life’s path, it is likely that you will be asked to provide a
summary of complicated materials for your boss, the board, for the public, or your friends
and family. In order to do so in an effective manner, you need to understand the
information well enough to be able to identify (and summarise) the most important
points, leaving aside less important details. Secondly, you need to consider the audience
you are presenting for as this will dictate the level of detail and background material
required to place your summary in context.
You will explore the Alan Hills meteorite controversy and the Apex Chert controversy,
using these (in)famous studies to critically assess what is a good biosignature and the
difficulties in confirming evidence of life in the ancient rock record, whether it be Earth
or Mars.
(1) Read the short papers in the folder ‘Assessment papers’ on Moodle.
Make notes, highlight parts you do not understand and find out what they mean.
Identify the key points. Reading and understanding scientific papers will be an
increasingly important part of your studies as you progress through your degree. The
abstract and conclusions sections of papers are the best places to get a broad overview
of the findings. The introduction section will ‘set the scene’ – the context to the new
study presented.
(2) Make a reasoned argument either for or against the discovery of microfossils in
either the Apex Chert or Martian meteorite ALH84001 (500 words). You can use figures
from the papers to communicate your points. You can also search for other published,
peer reviewed literature on the subject to strengthen your argument. Ensure all sources
and work that is not yours are correctly referenced, and include a reference list at the
end of your essay (not included in the word count).
(3) Using examples from the ALH84001 and Apex Chert papers to justify your answer,
do you think we will only find evidence of past microbial life on Mars through a Mars
Sample Return mission, or will in situ rover investigation of Martian rocks be
sufficient? (100 words)