Lab_5_earliest_fossils-1 (1)
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Apr 3, 2024
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GEOL 102
Earth History
Lab 5: 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)
For the first site, c in zircon, the earliest rocks to be known are from 4.1Ga years ago. These rocks are from the Jack Hills in western Australia. The main evidence of the page is that there was carbon activity that was found in these rocks. To which there was a trace of Carbon preserved in zircon 4.1 Ga years ago.
1
GEOL 102
Earth History
The next page that I looked at is Isua, which talks about a sedimentary rock from the Isua supercrustable belt. The rocks from this area are dated from 3800-3700 million years ago. In these rocks stromatolites were found and are used as to date rocks. These predate the previous most convincing and accepted evidence in the 3480-Myr-old formation of the Pilbara Craton.
The oldest well-established microorganism activity was established about 2,900 – 3,000 years ago. It was in Myr Pongola Supergroup of South Africa. A few more occurrences later than the Archean. The only possible older rocks are 3500 myr cherts in South Africa. The last site is about hydrothermal vents precipices, which were found to be at least 3770 million years. Furthermore, the number of years could potentially be 4280 million years. These sea floor hydrothermal vents were found in the Nuvvuagittuq belt in Quebec. 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).
When it comes to the strengths of each, they all have their own. C in zircon has carbon activity that was preserved. Along with that, zircon it is resistant which makes it reliable. Next, for Isua stromatolites that that are found in rocks that range from 3.8 to 3.7
billion years ago, offer concrete proof of prehistoric microbial populations. Following is the Pongola page. It had a lengthy history of microbial life on Earth is shown by the existence of microbe activity in rocks that date back to 2.9 to 3 billion years ago. Finally the last site that is left are the vents from Quebec. What Quebec has is that evidence of oceanic ecosystems can support life may of be found in the Nuvvuagittuq belt, where hydrothermal vents going back at least 3.77 billion years have been discovered. An early development of hydrothermal systems is suggested by the probable age of 4.28 billion years.
On the other hand, they did all have some weaknesses. The weakness for C in zircon is that carbon activity does not directly affect biological origin. Next, the weakness
of Isua is that the stromatolites overlap with other fossils which can mess with dating. For
Pongola, it has the draw back of the microorganisms activity being more recent. Finally, for Quebec the vents are debated since they abiotic processes can produce similar minerals. Isua has the best chance of having the oldest fossil, based on the evidence that has
been provided. The existence of stromatolites, which are typically accepted to be biological in origin, provide proof of prehistoric life. Their relevance is further increased by the fact that the age range of the rocks containing these stromatolites precedes other confirmed fossil possibilities. Despite the fact that each site has advantages of its own. 2
GEOL 102
Earth History
This is because stromatolites are directly associated with early living forms. For these reasons, I believe that Isua are the earliest fossil. 3
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