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25 Cards in this Set
- Front
- Back
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How long ago did life first appear on Earth? |
3.5-4.0 Ga |
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How do we know this? |
Isotope geochemistry (fractionation of 12C & 13C) |
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When was the Great Oxidation Event (GOE)? |
2.4 Ga
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Why was there not much oxygen before then? |
Chemically mopped up by ferric iron |
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When did eukaryotes arrive? |
1.5 Ga |
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When did chloroplasts arrive? |
1.2 Ga |
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What is the earliest evidence we have of chloroplasts? |
Fossilised Bangiomorpha |
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What are the three theories as to the early origin of life? |
1. Extraterrestrial (meteorites) 2. Energy through the atmosphere 3. Hydrothermal vents or warm springs |
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What are the key pieces of supporting evidence for the extra-terrestrial origin of life? |
1. Amino acids found on Meteorites (and Tardigrades can survive in space) 2. Gaseous methane emissions on Mars 3. Mars had an ocean and atmosphere 4. Earth was hit by meteorites up to 3.8 Ga |
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What are the arguments against extraterrestrial origin of life? |
1. Amino acids on comets are racemic - wrong stereoisomers 2. Doubt as to whether methane emissions are biotic in origin |
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Describe the method and results of the Miller-Urey experiment. |
Energy passed through a mixture of gasses rich in CH4, NH3, H20 and H2 for a prolonged period. Amino acids produced, including those found in proteins (e.g. alanine, glycine) |
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According to Miller & Urey, how may this process have lead to the origin of life? |
Amino acids collected in ponds, where polymerisation happened (assisted by clay) to create proteins. |
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What are the arguments for this origin of life? |
1. Atmosphere representative of Earth at the time 2. Volcanic activity cause extreme weather i.e. lightning 3. Hydrogen would not have outgassed (University of Waterloo, 2005) |
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What type of amino acids are produced in the Miller-Urey experiment? |
L-stereoisomers (racemic, not scalemic) |
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What are the arguments against this origin of life? |
1. Wrong type of amino acids 2. Atmosphere unlikely to be as Miller & Urey set it up to be due to volcanic activity (Green - 2011) 3. Hydrogen likely to have escaped into space |
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What temperature would hydrothermal vents be at? |
>400°C |
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Why is life unlikely to have originated at this temperature? |
Early proteins/organic molecules would have denatured or been unstable |
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What type of creature may be able to survive in this environment? |
Archaea, e.g. Pyrococcus furiosus |
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Who came up with the warm springs hypothesis? |
Mike Russell |
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What compound may have been instrumental according to this hypothesis? |
Iron sulphide (FeS) |
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How did chemical reactions start according to this hypothesis? |
Iron sulphide precipitated, forming concentration and redox gradients, powering chemical reactions |
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What was the next step to forming membranes? |
Long-chain fatty acids line up along the froth, improving division between the inside and outside |
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What process formed proteins inside the froth? |
Nucleotides join to form a nucleotide soup, leading to protein synthesis |
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Why might this hypothesis be convincing? |
1. We know biological reactions rely on chemical gradients (e.g. ATP synthesis from proton gradients) 2. Modelling of solute flow suggests this can happen |
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