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Thread: Grand Canyon fossil or geology question

  1. #1 Grand Canyon fossil or geology question 
    Forum Junior c186282's Avatar
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    I just got back from hiking the Grand Canyon. Down in the Super Group where the age of the rock is about 1 Billion years old I found many light sandstone rocks with spherical blackish-red sandstone balls in them. Any idea what these are?


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    Forum Radioactive Isotope skeptic's Avatar
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    I have not seen what you describe, but the 'balls' sound like concretions with iron oxide giving the colour. At about the age you describe, a great deal of iron was oxidised. This was a result of the massive chemical changes that occurred with the first photosynthetic bacteria. With oxygen molecules available to react chemically with other materials, a lot of iron was oxidised at about that age. Even today, as you can observe with rusting iron, atmospheric oxygen continues to convert any available iron to oxide. In the 1 to 2 billion year ago time, a lot of iron was available and consumed the oxygen released by bacteria.


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    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    Quote Originally Posted by skeptic
    I have not seen what you describe, but the 'balls' sound like concretions with iron oxide giving the colour. At about the age you describe, a great deal of iron was oxidised. This was a result of the massive chemical changes that occurred with the first photosynthetic bacteria. With oxygen molecules available to react chemically with other materials, a lot of iron was oxidised at about that age. Even today, as you can observe with rusting iron, atmospheric oxygen continues to convert any available iron to oxide. In the 1 to 2 billion year ago time, a lot of iron was available and consumed the oxygen released by bacteria.
    Which also happens to explain wonderfully how the photosynthetic system evolved despite being intolerant to oxygen
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    Forum Junior c186282's Avatar
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    Quote Originally Posted by skeptic
    This was a result of the massive chemical changes that occurred with the first photosynthetic bacteria.
    In the area that I was in there are many stromatolite fossils. However I'm not sure I was able to identify them. The group I was with got tired of me pointing at rocks and and wondering if that is a stromatolite fossil.
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    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    Quote Originally Posted by c186282
    Quote Originally Posted by skeptic
    This was a result of the massive chemical changes that occurred with the first photosynthetic bacteria.
    In the area that I was in there are many stromatolite fossils. However I'm not sure I was able to identify them. The group I was with got tired of me pointing at rocks and and wondering if that is a stromatolite fossil.
    In the grand canyon, I don't know if stromatolite fossils would be there. I'm not a pre-cambrian paleontologist though haha.
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  7. #6  
    Forum Radioactive Isotope skeptic's Avatar
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    Stromatolite fossils are extremely hard to identify. While they leave distinctive structures, those structures are not shells, or plating or bones. They consist of sand grains stuck together. Since sandstone also consists of sand grains stuck together, trying to distinguish between the two is next to impossible.
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    Forum Sophomore hokie's Avatar
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    Concretions are common in many areas. Concretions can weather out of the rock and be seen in as small balls. Sometimes pebbles or fossils in the rocks can be the 'seed points' for the concretions. There is a fossil deposit in Utah which has dark blotches around the trilobite fossils. Sometimes these shapes are mistakenly claimed to be human shoe prints crushing the trilobites. Outside of Vegas in the Red Rocks are some amazing concretions that have been covered by desert varnish. These concretions are strong enough to support human weight for rock climbing.
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