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Lab 6: Precambrian Observations

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Lab 6: Precambrian Observations Lab 6: Precambrian Observations How This Lab Will Work 1. Open a Word doc or similar on your computer 2. At various points I will ask you to answer a question based on the activities in this lab. 3. I will indicate these points by this symbol: Please answer these questions in your Word doc. 4. After you have assembled the answers into your Word doc, go to the course Canvas page. 5. On the module for this week there is a link to TurnItIn. 6. Please upload your document using the TurnInIt. 7. That completes the lab assignment. :) Topics Today 1. Your Lab Project 2. Stromatolites 3. Ediacaran examples Your Lab Project As you may recall from the syllabus a major item for the lab portion is the “lab project,” which was described there as: Your fossil observations, in combination with skills of photographing and drawing, will provide the foundation for you to construct a notebook. This notebook will include information, photographs, and drawings of the major fossils, organized by time period. The big idea here is that you will then have this as a personal reference. What you are going to do for the rest of the term is construct a fossil notebook, which will due on the last class meeting (17 Dec). Here’s what I’m looking for: 1. for each fossil, a one-page summary of that fossil 2. this summary should include: a. a sketch and/or photograph of the fossil, perhaps in various angles, and with a scale b. full scientific name, including genus and species (if applicable) c. notes about eating habits—how does this critter make a living? does it photosynthesize or is it a predator? an omnivore? a locavore? Geology 121 Lab 6: Precambrian, page 1 of 11 d. notes about defensive habits—how does this organism defend itself? (may not apply to Ediacarans) e. notes about lifestyle—does this move, or is it fixed? does it swim/crawl/fly? f. evolutionary relationships—what other organisms is it related to? For example, when we look at Archaeopteryx, it should be noted that it is related to theropod dinosaurs and birds. Phylogenetic diagrams may prove useful here in explaining relationships. 3. as a conclusion section to this notebook, you should include a phylogenetic chart showing the relationship (if discernible) between all the specimens in the notebook 4. if you need more than one page, that’s fine, but think each specimen should get at least the list above covered 5. outside research will help the detail of this project One of my intentions with this project is that you will hold on to this and use it in the future whenever confronted by a question about a fossil. For today’s lab I would make pages for: • stromatolites • Charnia masoni • Dickinsonia • Parvancorina • Tribrachidium • Spriggina Stromatolites https://sketchfab.com/3d-models/bitter-springs-stromatolite-domal-form- eac4c582285b4056ada427ef5e477c28 https://sketchfab.com/3d-models/stromatolite-chlorellopsis-coloniata- cornell-77ea493b45e64cff96532770062a069a Stromatolites are fossil structures created by cyanobacteria. Cyanobacteria were formerly called “blue-green algae,” but this name has been replaced because it incorrectly suggests they are eukaryotic algae, when in fact they are prokaryotic eubacteria. Stromatolites are a structure; rarely do we find examples of individual bacteria fossils, as these are exceptionally hard to fossilize. Stromatolites grow by accumulating “rings” that migrate over time upward. The basic idea in this is that because bacteria produce mucilage (similar to your mucus), this can trap material, such as calcium carbonate or clay. As these tend to block light for photosynthesis, the living surface must push through and form a new layer. Geology 121 Lab 6: Precambrian, page 2 of 11 Typically living stromatolites (as observed in places such as Shark Bay, Australia) contain three distinct layers, as shown in this diagram: The reason for this segregation of microorganisms has to do with how different wavelengths of light penetrate the upper layers. Specifically, cyanobacteria (blue-green) absorb shorter wavelengths of light (400, 500, 600-700 nm), which cannot penetrate as deeply as longer wavelengths (750, 900 nm). Other bacteria have evolved to exploit these unused zones in stromatolites. What is a general rule you can write to describe how light wavelengths of different wavelengths can penetrate into stromatolites? Geology 121 Lab 6: Precambrian, page 3 of 11 There are several different forms stromatolites take as they grow: Geology 121 Lab 6: Precambrian, page 4 of 11 1. Modern Shark Bay stromatolites grow about 350 mm/1000 years. In the first 3d model we saw a fossil of a stromatolite that was 5 cm in width. How long of a time period might be shown in that stromatolite? ___________________ 2. In the second stromatolite 3d model, what type of stromatolite would you say is shown? _____________________ Please answer these questions in your Word doc. Ediacarans https://sketchfab.com/3d-models/la-faune-dediacara-94e7a9dee4894e76a262fd4558110dde The Ediacarans (“ee-dee-ack-ar-anz”) are a very enigmatic group of organisms. Notice I didn’t say “animals” or “plants.” That’s because there is no consensus about what the bloody hell they were. Some have suggested that they are giant individual cells. There is also no consensus about if they went completely extinct, or if they evolved into modern organisms, in which case we could say that the descendants of Ediacarans are still among us. As Michael had in his presentation video link (https://www.youtube.com/watch? v=HKP3Hzy7F9g ), a living organism called Dendrogramma has intriguing similarities to Ediacarans. (https://en.wikipedia.org/wiki/Dendrogramma) There is not even complete consensus about what to call these; they are alternately known as the “Vendian fauna,” with members called “Vendozoans.” 3. This 3d model of an Ediacaran diorama looks pretty different from a model marine environment. What are some things that are different? ______________ Please answer these questions in your Word doc. Ediacaran: Charnia masoni https://sketchfab.com/3d-models/charnia-masoni-holotype-f93cb4393da3443fab6533e9ae8438c6 https://sketchfab.com/3d-models/charnia-masoni-de3b7168ae394b7dafda1c3e0e252b44 This particular fossil was spotted by a young boy (Roger Mason) while rock climbing on a cliff in Leicester, England. He took a rubbing and eventually this rubbing found its way to a geologist, who recognized the significance. Today Charnia masoni is named in honor of Roger Mason Geology 121 Lab 6: Precambrian, page 5 of 11 (who he grew up became a professor of geology). However, it later emerged that a young girl, Tina Negus, had in fact spotted the same fossil years before, but she had been ignored when she described what she had seen to adults. Her teacher had in particular dismissed her find because of the alleged impossibility of finding fossils in Precambrian rocks. There’s probably some sad hashtag to make for this story, but I don’t have the heart to do it right now. :( 4. Try to describe its shape: __________________ 5. Does the shape remind you of anything? __________ 6. Given its shape, do you think it was mobile or sessile (fixed)? ____________ 7. Do you see any eating apparatus? ___________________ 8. Do you see any reproductive apparatus? ___________________ 9. Do you see any circulatory apparatus? ____________________ Please answer these questions in your Word doc. If the parts can be thought of as “fronds,” what might that suggest about this organism’s lifestyle? I can think of two things in particular that live using “fronds.” Charnia masoni is classified as a “rangeomorph.” This is a “form taxon,” which means a group defined by shape rather than some other definitive feature. If we used “form taxon” criteria for other organisms, we might get some interesting pairings. Let’s say you had never seen a living dolphin or a living shark. On what basis might they belong to a “form taxon”? What is another example of a mistaken “form taxon” pairing? Rangeomorphs are distinct in having branching, fractal “frond” elements. Let’s explain that word “fractal” a bit more to help you understand/draw what you’re seeing here. Geology 121 Lab 6: Precambrian, page 6 of 11 Fractals are complex mathematical objects developed in the 1970s as computing increasingly became a part of mathematical inquiry. The fundamental idea is that fractals are repetitive elements that look the same at a variety of scales. Fern leaves are a good example of natural fractals. You can see in the picture to the right 3 main groupings of leaves. On each of these groupings, there are about 30 smaller leaves—but each of those 30 leaves has the same shape as the big grouping. That’s fractal geometry. In some ferns, this goes another level deeper, as in the example to the right: Here the main grouping has individual leaves, but each of those leaves has more identically-shaped leaves. The more you burrow into a fractal, the more you keep seeing the same shapes over and over. Of course, this is the limit for ferns. In mathematics, however, this fractal burrowing has no limit and infinitely spawns smaller and smaller versions of the whole. Even very simple mathematical equations, when repeated billions of times by a computer, spawn incredibly life-life and complex fractal shapes. (And today professional art rendering programs such as Maya use fractal algorithms to create realistic landscapes.) Another example worth considering is the length of coastlines. How long does the California coastline stretch? You could measure it at the state level and come up with a number. You could burrow down to the county level and come up with much more detail, and increase the length of the coastline. You could go to the level of an individual beach, increasing still the measured length.
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