The earliest evidence for life on Earth is

Geomicrobioloy Practice Questions

Basic concept (22 points):

Multiple Choice: Circle the best answer for each question (2 points each)

1.The earliest evidence for life on Earth is:

a.Banded iron formations

b.Stromatolites

c.Oxygen in the atmosphere

d.Micro-fossils in meteorites

2.Which of the following is more widely accepted for the origin of life?

a.Panspermia

b.Surface origin hypothesis

c.Hydrothermal vents

d.None of the above

3.If you amend methanogenic sediment with nitrate, what will happen to H2 concentration?

a.Increase

b.Decrease

c.No change

d.Difficult to know, because it depends on environmental conditions

4.Is a Domain of life:

a.Bacteria

b.Archaea

c.Eukaryota

d.All of the above

5.Synthesizes proteins in the cell:

a.DNA

b.Proteins

c.Ribosomes

d.Cytoplasmic membrane

6.Enzymes:

a.Are proteins

b.Reduce activation energy of chemical reactions

c.A and B

d.None of the above

7.What is the biologically available form of nitrogen?

a.N2

b.NO

c.NH4

d.N2O

8.Mineral evolution refers to a change over time in:

a.The diversity of mineral species

b.The relative abundance of minerals

c.The compositional range of minerals

d.The grain sizes and shapes of minerals

e.All of the above

f.Oxidation state of minerals

9.A facultative aerobe is:

a.Grows better in the presence of O2

b.Grows worse in the absence of O2

c.Does not care about O2

d.Requires O2 but at levels lower than atmospheric O2

10.What happens to the surface area of smectite after biological reduction of structural Fe(III)?

a.Increase

b.Decrease

c.No change

d.Unknown because it depends on environmental conditions.

11.An organism that grows optimally at a temperature of 15OC:

a.Hyperthermophile

b.Thermophile

c.Psychrophile

d.Mesophile

12.         

Briefly describe how geological and microbial processes interact and give an example of such interaction (hint: it’s a mutual interaction, e.g., bi-directional; think about geological environment, limiting conditions and impact of life on the geological process/environment).

13.         

Organisms are classified by their carbon and energy source. Describe the carbon (organic or inorganic carbon) and energy sources (needs) for chemolithoautothrophs, photoautotrophs, and chemoheterotrophs.

14.         

Why do microbes weather minerals? 

15.         

Give two mechanisms of how microbes weather minerals?

16.         

Sketch concentration profiles that would indicate the following microbial metabolisms (include the relative changes in concentrations of O2, NO3-, Fe2+, SO42-, CH4 and indicate where with depth these organisms would thrive):  Aerobic heterotrophy, iron reduction, sulfate reduction, nitrate reduction, aerobic methanotrophy (methane oxidation), and methanogenesis.

Note: now that it’s electronic, you can use whatever you feel comfortable to do this. You can use drawing tools in word, powerpoint, even draw the profiles by hand on a piece of paper. Then you can take a picture and send it to me via email.

17.

Can a mineral be formed by both BCM and BIM? If so, how would you determine its biogenic origin?

18.

Refer to the following electron tower to answer this question:

a.If you use structural Fe(III) in smectite as the sole electron acceptor and methanol, acetate or lactate as 3 possible electron donors and carbon sources in a neutral pH growth medium. Which one should be most efficient (consider rate and extent) in reducing the Fe(III) and why?

b. If the oxidation product of lactate, pyruvate, were able to serve as an electron shuttle, would your answer to part a) be still true?

c.  What are some consequences of microbial reduction of Fe(III) in smectite on soil properties? How would a farmer mitigate these negative impacts?

19.  If there is life on Mars, do you necessarily expect to find magnetite crystals in Martian meteorites that have the same characteristics as those produced by magnetotactic bacteria on Earth? Why and why not? Be specific.

20.  

Geomicrobiologists have cultured a great diversity of microorganisms in various geological environments but they know that an even greater diversity exists, especially in extreme environments, despite the fact that they have never seen these organisms or grown them in the laboratory. How do they know greater diversity exists in nature? What types of methods do they use to detect the diversity?

21.  

A friend of yours in Spain sent you a picture (see SEM picture below) and asked for your advice.  She was studying rocks (volcanic tuff) from the K/T (Cretaceous/Tertiary) boundary, and all of sudden she saw lots of microbe-like objects in her rock (the rod-shaped objects near the center of the image).  How would you help her determine if these objects are really microbes?  This task could be very significant if microbes exist in such old rocks (the K/T boundary is about 66 million years ago when dinosaurs went extinct!).  Remember: you are a geomicrobiologist by training, so you look for both geological and microbiological evidence.  Come up as many reasons as you can. In other words, give me your approach of how you would prove or disprove whether or not these are indeed microbes.