TakeHome_Lab_2
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Iowa State University *
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Geology
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Apr 3, 2024
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GEOL 102
Earth History
S23
Take home lab 2: Earth’s Earliest Fossil
Purpose
: We know that today, Earth is full of life. Organisms can be found in every environment on the planet, even far below the surface. Exactly how and when life first began, however, is unknown. In this lab, you will examine four
proposals for Earth’s earliest fossil. After reading the abstract from four papers, along with looking at images and graphs, you will summarize each candidate for earliest fossil, and then using your summary provide evidence for which one you think makes the strongest case. Use the information on this assignment along with
the materials in Canvas to answer the questions. To turn in: This word document, with questions answered, to Canvas. Background: A fossil is a remain left by life. We might be familiar with some types of fossils from large animals: dinosaur bones, seashells, corals. We may even be familiar with trace fossils,
which are things like footprints or burrows, and record evidence of an organism’s behavior. These fossils are great, but skeletons, shells, and other easily preserved bio-materials only date back to about 550 million years ago. Prior to this, during the Precambrian, we instead must be more creative. All life, prior to about 650 million years ago, was single celled. These organisms don’t usually leave great fossils, though rare ones do occur. Instead, what they leave are either geochemical signatures of their presence and activity or structures called stromatolites. A stromatolite is a layered, conical type of structure that can be produced by a microbial mat. That is, a bunch of microbes who all live together and are kind of sticky, so they build up layers and layers of cells and sediment they trap. Some stromatolites are made by life, and some aren’t. There may be a number of challenging terms and ideas in this assignment. You are more than welcome to look for outside resources. One that could be helpful is the “A dictionary of Geology
and Earth sciences”. You can access this through the library online https://www.oxfordreference.com/display/10.1093/acref/9780198839033.001.0001/acref-
9780198839033
Materials:
There are four pdfs included in the assignment in Canvas: 1.
Vent_quebec
2.
Strelley_pool
3.
C_in_zircon
4.
Isua
Questions. 1.
For each of the four sites, using the abstracts and figures, summarize the proposed sample
for each Earth’s earliest fossil. Your answer should describe the location, age, what is the major evidence, and how the authors support their claim. Focus on just summarizing what the authors say, you will give your thoughts in the next question. Plan to write about
a paragraph for each one (20 points)
a.
The first one ages the first from of life from 3,770 Mya, as far back as 4,280 Mya.
They think it started from hydrothermal vents in Quebec, Canada. The structures that they are studying are micrometer-scale haematite tubes and filaments with mineral assemblages that resemble microorganisms. 1
GEOL 102
Earth History
S23
b.
The next theory is based on stromatolites. They already are some of the oldest findings and most consistent to the oldest life, but here it is claimed that there is new evidence for some as old as 3,500 Mya. This finding is in Western Australia.
c.
The third theory is based on carbon dating. Based on the zircon crystals from the Jack Hills in Western Australia there is one crystal that was found with a organic carbon ratio of C13. They date this to be 4.1 Ga with give or take .01 Ga in spread. d.
The last study is also based on stromatolites. They found textures that date to 3,700 Mya, older than the current 3,480 Mya dating in Australia. Their discovery took place in Isua supracrustal belt, southwest Greenland. There is not much else to go on with this article.
2.
Now, synthesize your notes. What are the strengths and weaknesses of each site? What strikes you as good evidence and poor? List these for each, then write a few sentences about which site you think is the best supported
for earliest fossil site. This answer should be about 2-3 paragraphs long (30 points).
a.
In my opinion I think that the last article has the worst evidence. The reason I believe this is because the images are not very conclusive. To my untrained eye it just seems like it can have other causes than stromatolites. The next one that rides this same pattern is the one that took place in Quebec. It also basis a pattern that looks similar to a certain organism, and although it can be what they think it is, there does not seem to be conclusive evidence from what they show here. b.
The remaining two are slightly stronger in my opinion because they take place in Western Australia, which is where we have seem a lot of Earth’s earliest history thus far. I think both articles play off each other nicely. The piece of evidence that
strikes me as best is carbon dating. Based on the graph of which carbon levels show organic carbon is a good visual to support their theory. 2
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