Lec 5: Early Life on a Young Earth Flashcards
Describe conditions on the early Archean Earth
- reducing atmosphere, no free oxygen
- no ozone layer to shield from UV radiation
- meteor bombardment
what is a biosignature?
any substance that provides evidence of life
- fossils, chemical fossils, isotopic signatures
What are chemical fossils?
- biomarkers
- certain compounds’ structure can be preserved through time
- lipids!
What do isotopic signatures show us? How do we get them?
Stable carbon isotopic signatures are the ratio of C-12 to C-13.
Abiotic and biotic processes have difference stable carbon isotopic signatures.
What was found in the Apex Chert in Australia? What does it tell us?
- Oldest known form of life on Earth
- not sure if the microfossils found in the rock are life, but their isotopic signature is consistent with life
How are stromatolites formed?
1) bacteria secrete mucus
2) grains of sediment collected
3) grains stuck together with calcium carbonate
- oldest stromatolites occurred 3.5 Ga ago
- modern stromatolites formed by cyanobacteria (autotroph, photosynthetic, everywhere)
What were ancient stromatolites made up of?
- anoxygenic phototrophs.
- uses other substances instead of water as an electron donor in the photosynthesis
What other types of bacteria existed during the Archean?
sulfate-reducing microbes
- are heterotrophs
- live in anoxic conditions
- use SULFATE instead of oxygen as an electron acceptor
Were the first cells anaerobic or aerobic? Were they heterotrophs or autotrophs?
anaerobic heterotrophs, because there was an abundance of organic molecules for them to eat
Why did photosynthetic organisms develop?
Once organic molecules became scarcer, photosynthetic organisms were favored
When did oxygenic photosynthesis emerge?
Oxygenic photosynthesis, like that performed by cyanobacteria, emerged at the end of the Archean, when oxygen concentrations in the atmosphere rose. (about 2.5 Ga)
What caused the Great Oxidation Event?
the activity of oxygenic phototrophic microorganisms (Cyanobacteria)
Why did it take so long for oxygen to accumulate in the atmosphere?
BIF and organisms started using oxygen for heterotrophic respiration. Oxygen could only start accumulating once all the free Iron in the seawater was consumed.
How do red beds form?
When iron is weathered out of rock in the presence of oxygen
How did the Great Oxygenation Event affect diversity?
diversity increased at the end of the Great Oxygenation Event. Their small size indicates that most were prokaryotes
