Lab 6- Virtual Pilbara Field trip (1)
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GEOL 102
History of the Earth
Name: Emanuel Moreno
Lab 6: Virtual Field Trip – Pilbara
Purpose
:
In this investigation, you will explore some of the most well preserved Archean rocks using a Virtual Field Trip (VFT) put together by Arizona State University: https://vft.asu.edu/
These sites are all found on the Pilbara Craton
, in Western Australia. This area preserves some of the very best examples of Archean geology anywhere on Earth. It’s also relatively dry and remote, and thus has excellent exposure. Specifically, we’re going to focus on a few concepts:
1.
What rocks are typical of this area from the Archean
2.
What we look for as signs of early life
3.
Become familiar with the Pilbara craton in general, as it’s a crucial place in understanding early Earth history! Have fun!
Part I. Marble Bar (18 points) Enter this field trip here: https://vft.asu.edu/VFTMarbleBar/panos/MarbleBar/MarbleBar.html
Rocks at Marble Bar represent one of the oldest preserved sedimentary sections on Earth. They can give us information about the environments where very early life may have first appeared and evolved. Explore the area to answer the following questions. Main Marble Bar Chert Area: 1.
What is the law of original horizontality? (2 points)
Any tilting or folding that deviates from the horizontal orientation is indicative of geological activities that occurred after deposition.
2.
What types of rocks are here? (2 points)
A couple types of rocks that are there are, chert and Banded Iron Formation.
3.
How did the banding in the Marble Bar Chert form? (4 points)
The banding could have been formed for a couple of reasons, one of which is deposition. The different layers of chert could have been deposited over time. Another reason is the conditions in the environment. The changes in ocean chemistry or oxygen levels could of affect the layers. Finally, another reason could have been the variation in sediment 1
GEOL 102
History of the Earth
supply. The Marble Bar Chert's alternating banding may have resulted from shifts in the availability of silica- and iron-rich sediments.
Upper ridge: 4.
What types of banding do you see here? Which types of rocks are preserved here? You’ll need to make observations, there are no videos or pictures here. (2 points) The banding that I see is alternating layers of chert and iron-rich minerals. The main banding seen in Marble Bar Chert is made up of layers of chert, which is usually light
in color, and minerals rich in iron. The types of banding that I see preserved are banded iron formation. Outcrop area: 5.
What’s a pillow basalt? (2 points) A pillow basalt is a underwater basaltic lava flow that is distinguished by structures resembling pillows that are formed when the lava cools quickly and solidifies in the presence of water.
6.
What was the depositional environment shown here? How far below the surface of the water were these rocks deposited? (2 points)
It is likely that there was marine life in the past. The rocks were deposited at depth range about 0 to 200 meters. General question: 7.
What kind of environment did early life most likely live in, at least in this location? That is, based on the rocks and minerals here, what was the environment like then? (4 points)
Based on the environment, the life that most likely lived there was marine life. Chert and banded iron formations indicate that the material was deposited in ancient marine basins, maybe close to volcanic island arcs or continental shelves.
Part II. Dresser Formation (14 points)
The Dresser Formation preserves the oldest stromatolites on Earth! You’ll see some samples of these in the in person lab, but stromatolites are sedimentary structures that are likely formed by microbes. Enter this field trip here: https://vft.asu.edu/VFTDresser/panos/Dresser/Dresser.html
2
GEOL 102
History of the Earth
Upper Dresser Formation: 8.
What’s the name of the area here? How old is the Dresser formation? (2 points)
The name of the area is the Upper Dresser Formation. It is about 3.48 billion years old. 9.
What is the evidence that microbes made the stromatolites formed here? (4 points)
Some of the evidence that microbes made stromatolites were formed here are the isotopic signatures, suggesting that the carbonates were precipitated by microbial photosynthesis. Another piece of evidence is the texture which Further evidence of microbial participation is seen in the interior architecture of the stromatolites, which bear a striking resemblance to current stromatolites created by microbial populations.
Lower Dresser Formation: 10. What type of fossils are preserved here? (2 points)
The types of fossils that are preserved here are filamentous structures interpreted as microbial
mats or microbial filaments.
General question: 11. What does the depositional setting (i.e., water depth) at this site, and how do we know? What does this tell you about the environment in which early life lived? How do we connect the geology of this area to the biology of what was living? (6 points)
Based on characteristics like as microbial mats and stromatolites, the Dresser Formation suggests a depositional environment of shallow marine or intertidal settings.
These formations imply enough sunlight for photosynthesis and an appropriate environment for protozoa. Through the adaptation of creatures to flourish in these conditions and the preservation of fossils offering insights into the variety and ecology of early life, the geological evidence shows to the biology of what lived there. All things considered, the Dresser Formation offers important hints regarding the genesis and development of life on Earth within prehistoric shallow marine habitats.
Part III. Karijini Gorge (20 points)
Karijini gorge is a national park in Western Australia. It preserves some of the world’s most awesome exposures of Banded Iron Formations.
These are units that were relatively common in the Precambrian (Archean and Proterozoic), but are much rarer in the Phanerozoic. They are comprised of alternating layers of silica and iron oxide, and there has been a lot of research in trying to figure out how they formed! BIFs are often mined as iron ore, and the units in Western 3
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GEOL 102
History of the Earth
Australia are some of the biggest deposits in the world. Iron ore from this area is carried by autonomous trains to a port in Port Hedland, where it is shipped out, mostly to China. We will explore the science behind these deposits in this section of the lab.
Enter this field trip here: https://vft.asu.edu/VFTKarijiniGorge/panos/karijinigorge/kg.html
First, click the “Close to Rocks” arrow, and watch all the videos in the “Dales Gorge Overview” icon. To answer the questions below, you’ll need the overview videos and all the videos in both the “Dales Gorge Layers” and “Red Rock, Iron, and Chert” icons, which you can get back to by clicking “Close the Falls”.
12. Describe the physical characteristics of these units. Include in your answer the environment of deposition and what minerals are found in the layers here. Please outline evidence for the depositional setting as well. (4 points)
The environment is rich of Iron layers that are dark colors as well as silica rich layers which are light colored. The rocks extend for hundreds of kilometers. The evidence shows that there was probably an oceanic source that got water there.
13. Is there a lot or only a little organic carbon found here? (2 points)
There is little organic carbon found here.
14. What “biosignatures” are found in the layers here? (2 points)
Microbial structures and textures that point to the existence of prehistoric microbial life are among the biosignatures discovered in the strata.
15. How much iron is there in these rocks (a lot or a little)? What was the source of the iron? (2 points)
There is a lot of iron in these rocks, and the source of the iron is likely from hydrothermal vents or submarine volcanic activity.
Next, click “Down the Canyon”. Watch the videos in the “BIFs and evidence of oxygen” and “Microbes and rust” icons. Answer the following questions. 4
GEOL 102
History of the Earth
16. What is the conventional interpretation of how BIFs formed? (4 points)
It was formed by precipitation of iron and silica from ancient oceans in the basin, possibly triggered by changes in ocean chemistry or the activity of early microbial life.
17. What lines of evidence do we use to detect the presence of oxygen in the rock record? (2 points)
Some of the evidence that was found to use to detect the presence of oxygen is there was some rusting in the iron oxide minerals due to the red coloring.
18. Are there types of microbes that can do photosynthesis but NOT make oxygen? How would these organisms impact the formation of BIFs? (2 points) Yes, there are microbes that can do photosynthesis that do not make oxygen. These organisms would impact the formation of BIFs by influencing the chemical composition of the surrounding environment and potentially participating in iron oxidation or precipitation processes.
19. How does the history of Earth and it’s oxygenation inform our search for life elsewhere? (2 points)
It helps us by understanding, by providing insight into the conditions necessary for the development and sustenance of life. Understanding how oxygen levels changed over geological time helps scientists identify potential habitable environments on other planets or moons, guiding the search for extraterrestrial life.
There is one more stop down the canyon if you wish to explore it! Down here are examples of natural asbestos outcrops, that (gulp), used to be mined.
Part IV. Summary (8 points)
Write a couple paragraphs summarizing the paleoenvironments you’ve seen on this set of field trips. Focus on the similarities and differences between the sites, and how they record the environment, activity, and evolution of early life on Earth. Your answer may include textural evidence, geochemical evidence, or a combination of the two as supporting information. 5
GEOL 102
History of the Earth
Exciting insights into paleoenvironments and the development of early life on Earth are provided by the field trip to Karijini Gorge and the same examination of Dales Gorge. These locations have important geological features, especially Banded Iron Formations, which provide information on conditions on Earth's surface in the past. The alternating layers of silica and iron sediments in both places show deposition in prehistoric marine life. These formations include iron oxide minerals, which suggests that there have been periods of oxidation, brought on by changes in ocean chemistry and the activities of early microbial life.
There are noticeable diferences across the locations even with these similarities. Large-scale BIFs are seen in Western Australia's Karijini Gorge, suggesting protracted iron deposition and sedimentation times. The length of the rocks in this area are hundreds of kilometers. On the other hand, distinct geological histories or depositional circumstances may have shown in differences in the thickness of BIF layers at various locations.
These sites' geochemical and textural data show important development of early Earth life. The presence of ancient microbial communities is showing that by the microbial structures and textures that have been retained inside the BIFs. Furthermore, hints about the presence of oxygen and the prehistoric oceans may be found in the distribution of specific trace elements and mineral assemblages. Scientists can better understand Earth's early biosphere and its effects on global biogeochemical cycles by examining these environments.
6
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