L1 Origins Of Life Flashcards
What are the 6 essential elements
Carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus
What are 3 fundamental conditions for life on earth
Essential elements,
Continual source of energy,
Temperature allowing liquid water to
What are two continual sources of energy
Solar or geothermal
What are the conditions where no life would exist
150C and 1atm
When was the earth formed
4.5 billion years ago
At what period was the earth formed
Hadean eon
How were the elements up to iron formed
Sun released hydrogen
Heating hydrogen formed helium and other elements up to iron
How were elements greater than iron formed
Supernova
What geological events bring new elements to an environment
Meteor strikes
What are the charges of the crust and core
Crust highly oxidised, core very reduced
What is the earths core made of
Iron
What is the crust made of
Silicon dioxide
Also carbonates and nitrates
Could life have existed before it evolved to what is is today? And how?
Life could have existed and been destroyed by repeated meteor bombardment and then only exist in deep rock
What was the early atmosphere made up of
Most carbon dioxide, similar to Mars
What would have happened if carbon dioxide had been continued to be released by all life
Earth would of continued to warm and life could not of existed
The atmosphere absorbs light and converts it to…
Heat
Example of a planet where there is too much carbon dioxide
Venus
Example of a planet where there is too little carbon dioxide
Mars
What could have early microbial action caused
The ice age
What may have reversed the ice age
Evolution of methanogens
What is light driven carbon dioxide fixation
Photosynthesis
When did photosynthesis evolve
At leat 3.4 billion years ago
What was the trend when the atmosphere was oxygenated
Would’ve fluctuated with a general upwards trend
Why did oxygen conditions fluctuate
It was too toxic to most life at the time
Why can earth be referred to as a closed biosphere
Everything currently here is what can be used, nothing more
How are products linked by metabolism between living organisms
Products from one type of metabolism are linked to other biological processes
Products released by one are used by another - food, biomass etc
How long ago did life evolve
3.8 million years
What is the name of the time period where life evolved
Achaean eon
How was life able to develop
As stable oceans formed
Why is water so important for life
Remains liquid over wide temperature range
Is a universal solvent
Allows membranes to form
What are 4 evidences for the evolution of life 3.8MYA
Fossils
Isotopes ratios
Biosignatures
Oxidation state
What two things can be used as fossils
Stromatolites and microfossils
Where are stromatolites found today
Shark Bay, Australia
What condition of Shark Bay allows stromatolites to survive and why
High saline pools = no predation
How is the structure of stromatolites formed
Mucilage traps calcium carbonate, cementing biofilm and creating structure
Sediment-trapped mucilage forms rocks over time
From how long ago do stromatolites show evidence of life
3.4BYA - Archaean period
How do stromatolites fail to show evidence of life
Cannot see cells in fossils
How far back can microfossils be dated
2 BYA
What makes fossils form
Minerals precipitate
What are the advantages of using microfossils
Cell forms are visible and measurable
What else could have formed microfossils
Abiotic factors
Why do microfossils not appear before 2 BYA
Archaean rock was not compatible as it is metamorphic which is modified by temperature and pressure which destroys the fossils
Only sedimentary rock forms these kinds of fossils
Give an example of enzymes selecting isotopes
Carbon dioxide fixing RubisCo prefers carbon-12 over carbon-13
What happens to the carbon in cells
Converted to calcium carbonate
How can the difference in C12 and C13 be measured
(C13 / C12 (of experimental rock) - C131 / C12 (of standard rock))
Divided by (C13 / C12 (standard rock))
All timesed by 1000
What other element can be used to show enzymes selecting isotopes and how far does this date back
Sulphur 34 and 32
From 3.5 MYA
Advantages of using isotope ratios
Highly reproducible, provide physical measure
Strong evidence for dating earliest life
Can be used to calibrate phylogenetic trees
Disadvantages of using isotope ratios
Only tells us life existed, not what it looked like or what it did
Cannot guarantee they are not produced abiotically - can’t prove a negative
What will the amount of C-13 be in a biological source
Depleted
What would a minus value for the difference in carbon isotopes show
Minus value indicates a depletion of C-13 compared to C-12
What type of ion is soluble
Crustal ferrous (Fe2+)
What is an oxidised ferric ion
Is it soluble
Fe 3+
Insoluble
How can iron ions show varying oxygen concentrations
Layers of Fe3+ in sedimentart rock show alternating oxic and anoxic conditions
Grey layers of silicon oxide and red layers of ferric oxides
What are 3 possible sources of energy in early Archaean oceans
Oxidised forms of iron, nitrogen or sulphur interacting with hydrogen and driven by light reactions
Light-driven ion pumps creating gradients across memebranes
Metahnogenesis (2H2 + CO2 -> Ch4 + H2O)
What are the 3 models proposed for crearting life from energy
Prebiotic soup
Metabolist model
RNA world model
Who came up with the prebiotic soup model
What experiment was carried out
Oparin and Miller
Common compounds (hydrogen, water, methane) put under heat and pressure forms biomolecules like gylcine. Eventually develops proto-cells but this is large leap
What is the assumption of Oparin and Millers simulation and is it true
No oxygen present
Some evidence oxygen was present and could’ve reacted with N, Fe, S in prescence of UV light
What are arguments against Oparin and Millers experiment
Big leap from amino acids to functional proteins and cell formation
Elements may have been too dilute in ancient oceans - shallow coastal pools, or intertidal surfaces seem a more likely source for these reactions
How was the early cell membrane formed
Which theory does this stem from
Micelle shaken to form a bilayer
Formed from amphipathic fatty acid glycerol esters
Metabolists model
How was each amino acid formed
Which of the 3 theories does this stem from
From a component of the TCA cycle and 2 dinucleotides - went on to form basis of genetic code
Metabolists model
What is the nutrient cycle in the metabolist model
Self-sustaining carbon dioxide based metabolism similar to citric acid (TCA) cycle which was catalysed by metal sulphides
What does the RNA world model account for that is not covered in other models
The production of macromolecules that encode complex information
Why is it RNA model and not DNA
RNA uses uracil which is produced earlier than thymine (DNA)
How did adenine form in the RNA world model
From NH3 and carbon dioxide in ancient oceans
