Lecture 25: The Archean Biosphere Flashcards
-How did Life Evolve? -Evidence for Achrean Life
What are the four things the first cells needed to create?
1) Proteins
2) Nucleic acids
3) Carbohydrates
4) Lipids
What is the differentiation of Earth?
The organization of Earth into layers (core, mantle, and crust) due to gravity.
What are komatiites?
Rocks formed from ultramafic lavas once temperatures dropped below 1000°C
How old is the oldest rock?
4.0 Gyr (billion years)
What was the atmosphere like on early Earth?
- High Co2 levels (10 bars)
- High greenhouse gases
- No free O2
What is the ‘Organic Soup’ model of how organic compounds may have arisen?
Key prebiotic monomers were formed when reduced gases in the atmosphere were subject to UV irradiation and electrical discharges.
-They then condensed to form more complex compounds, such as amino acids, which accumulated into seawater.
What was one major problem with the ‘Organic Soup’ model?
Giant impacts would have constrained the timing of life’s origin at the Earth’s surface.
-Impacts would have vaporized rock and evaporated the upper water column, and perhaps the entire ocean
What is the most accepted theory on how life arose on Earth?
The theory that states that life would have started around hydrothermal vents
-Minerals surfaces could have served as templates for further polymerization reactions
Where does evidence for ancient life come from?
- Microfossils
- Biogenic structures
- Isotopes
- Biomarkers
What are microfossils?
The preservation of fossils that are microscopic in size.
Why are stromatolites (biogenic structure) the best piece of evidence for ancient life?
Because bacteria get buried under sediment then want light so the bacteria grow upwards, causing columns in the stromatolites.
-The columns are proof of bacteria
What is oxygenic photosynthesis?
Photosynthesis with oxygen
What is anoxygenic photosynthesis?
Photosynthesis without oxygen
How are Microbially Induced Sedimentary Structures (MISS) formed?
By microbial mates of filamentous bacteria trapping siliciclastic sediments in more
energetic tidal flat settings.
What important about MISS
- Can go back to 3.2Gyr
- Can see structures in the rock record that look like bacteria that would grow on river beds
How are isotopes evidence for ancient life?
Because the transformation of inorganic carbon via autotrophic pathways into organic carbon involves the preferential incorporation of the lighter isotope, into the organic phase, leaving behind a reservoir enriched in the heavier isotope.
How are biomarkers evidence for ancient life?
-They retain some resemblance to the original biological molecule, even after a long history of decomposition
What are biomarkers?
Organic compounds derived from more complex precursors to provide information on their relative abundance in ancient environments.
When did cyanobacteria evolve?
Ranges from 3.5 to 2.7 billion years ago
Why are cyanobacteria important?
They learned to split water to generate reducing power to fix CO2, and in doing so, released free oxygen to the environment
When did oxygen accumulate in the atmosphere?
According to the rock record, around 2.5 Gyr
- “The Great Oxidation Event”
