The Development of Life on Earth Flashcards
Lectures 5.1-6.4
What is the central dogma of biology?
The flow of genetic information in all biological cells. Specifically RNA to DNA in 3 processes:
1. Transcription
2. Translation
3. Replication
What are the 4 things about water that make it a necessity for biological growth?
- Universal solvent
- Ability to dissociate molecules into positive and negative ions, critical for biochemical reactions
- Osmosis
- Maintaining cell shape and cell membranes
What is the name for an organism who thrives in <20℃?
Psychrophiles.
What is the name for an organism who thrives in 15-45℃?
Mesophiles
What is the name for an organism who thrives in 45-80℃?
Thermophiles
What is the name for an organism who thrives in >80℃?
Hyperthermophiles.
What is the name for an organism who thrives in pH of 5-9?
Neutrophiles
What is the name for an organism who thrives in pH of <2?
Acidophiles
What is the name for an organism who thrives in pH of >10?
Alkaliphiles
What are the nutrients required for life?
Carbon, mainly. Autotrophs convert inorganic carbon into organic, and heterotrophs consume this.
Metals are also required.
What was earths primordial soup?
Biologically important molecules such as methane, ammonia, water and hydrogen self assembling into simple living cells.
Describe the RNA world hypothesis.
- RNA molecules catalyse replication, meaning they can perpetuate their own evolution. They compete and the best lives on.
- Chemical pathway discovered that RNA nucleobases were found in primordial soup that had been wet and dried.
What are the unsolved questions for the RNA world hypothesis?
- Unclear on if RNA or proteins came first
- No energy source
What is the geological support for RNA world?
The wet and dry cycles promote necessary reactions to form polymer. However there is no record of a stable wetting and drying environment.
Describe the Metabolism hypothesis.
- Chemical gradients needed life as a series of self sustaining chemical reactions that produced biomolecules
- Would have provided molecules and energy needed to fuel them
- Primitive bacteria were then chemosynthetic thermophiles
What are the unsolved issues with the Metabolism first hypothesis.
There is no way to store genetic information to pass on through evolutionary processes.
What is the geological support for the metabolism first hypothesis?
- Hydrothermal alkaline vents with hot temperatures, energy gradients, biochemical compounds and metals.
- These can produce protocells with iron sulphide membranes
However there is no clear link for how it all ended up in a single walled membrane to form a prokaryotic cell.
What are the defining characteristics of prokaryotes?
- No membrane bound organelles
- 70s ribosomes
- Asexual reproduction via binary fission
What are the differences between bacterial and Archean cell membranes?
Archaeal cell walls have isoprene chains that makes them able to withstand extremes.
- They also lack peptidoglycan which bacteria have an use for strength
What are the defining characteristics of Archaea.
- S layers form cell walls combined with methanochroitin (very strong) and sheaths linking tubular proteins
- Have pseudomurein (stronger than peptidoglycan)
What are Stromatolites?
- Bio sedimentary structures formed of microbes and sediments
- Form microbial mats from falling sediment, allowing for vertical growth
- Built by photosynthetic cyanobacteria
What is the issue with stromatolites?
Easy to mismatch with other lines of evidence from biomarkers. They could be from abiotic prosses?
What is the oldest Eukaryotic fossil?
Grypania, 2.1 Ga.
- Possibly cyanobacteria or algae
- Isn’t DEFINITELY a eukaryote
What is the oldest uncontroversial Eukaryotic fossil?
Acritarchs. 1.8 Ga.
- Organic walled microfossils with complex wall ornamentation
What is the oldest fossil tied to a modern group?
- Bangiomorpha pubescens, 1.05 Ga
- Red algae
- First evidence of sexual reproduction
What are the three fossil types?
Body
Trace
Chemical
What drove the snowball earth periods? What came out of them?
Driven by: Runaway albedo effect of expansion of ice sheets followed by volcanic emissions
Arose: First complex animal fossils due to extreme selection pressure of fluctuating earth and limited habitats
What is multicellularity defined by?
- Cell differentiation
- Cell signalling
- Co ordinated growth and development
- Division of labour
- Independent cells in an organism
What were the first organisms to perform photosynthesis and what did they create?
Cyanobacteria performed in chloroplasts.
- Evidence for this is fossilised bubbles in stromatolites which form reefs
What is a proxy?
- Proxies are a measurable quantity
of something that substitutes for
something else that is no longer
measurable
What are the three proxies that help us constrain O2 over time?
- Mass independent fractionation of sulphur isotopes
- Iron redox geochemistry
- Uraninite
What is isotope fractionation?
When some chemical process partitions a mixed pool of isotopes into pools of unique ones.
How were early sulphur isotopes fractionated?
- Sulphur gas oxidised to H²SO⁴ and rained out as sulphate
- Sulphur gasses accumulated in the atmosphere and underwent photochemical reactions
- These resulted in unique geochemical signatures resulting from mass independent fractionation
How can we use these sulphur isotopes to detect oxygen amounts?
- Values of sulphur isotopes below/above 0 signify isotope fractionation
- The process of sulphur gas being oxygenated cant occur without oxygen so there must have been oxygen if there is no MIF.
Why are there no Red Beds before 2.2Ga?
Iron rich minerals were not oxidised and reduced iron weathered away into the ocean. When atmospheric O2 accumulated, iron rich soils were oxidised and turned to rust.
Describe how Banded Iron formations form.
- Composed of alternating iron rich and iron layers of chert
Increase when ocean oxygen makes iron oxides and then oxygen in the atmosphere rises, as well as when oxidative weathering of soil caused an increase of sulphur in the ocean.
Increased again when iron was removed in a brand new geochemical pathway (snowball)
What is Uranitite?
- Rare today as it is extremely sensitive to oxidation
- So if there is any, there isn’t any oxygen.
- Forms clasts in sandstones.
What new proxy appeared after plants?
Wildfire records, using charcoal. We use it to estimate minimum oxygen levels once it appears.
What are the three evolutionary faunas according to John Sepkoski?
Cambrian, Palaeozoic and Modern Fauna.
