3/ origin and early evolution of life Flashcards
early history of earth - 4600 Ma
- earth formed
- begins to differentiate into core and mantel
- moon forms - same geochemical comp as earth
3750 Ma
- age of oldest rocks on earth
- earth cooled enough to solidify crust, oceans start to condense out
what are the oldest rocks on earth
isua supercrustal group, greenland
> 3800 Ma
- progress delayed by continued bombardment of large objects
- released energy enough to boil off forming oceans and atmosphere
< 3800 Ma
- bombardment decreases
- planet cools below a threshold that allows oceans and atmosphere to condense out
how did early atmosphere and ocean form, what was it like
- volcanic outgassing of H20, N2, CO2, CH4, NH3, H2, H2S
- H20 condensed to form oceans
- H2 lost to atmosphere
- earth had a reducing atmosphere (oxidising today)
- iron rich ocean w no CO2 dissolved in it, just nasty sulphurs
alternative theory for where water on earth came from
- comets
- too small, doesn’t explain all water
3500 Ma
- 1st fossil evidence for life on earth
- hence 300 million year window life evolved under from when conditions deemed to allow life
panspermia theory for the origin of life
- life evolved elsewhere then transported to earth
- doesn’t solve origin of life just shifts issue
- most likely impossible - hostile space environement
3 approaches to solving the origin of life
- analyse prokaryotes and attempt to reconstruct their common ancestor - simplest prokaryote
- compare duplicated genes potentially enabling us to reach back beyond that ancestor and estimate earlies components of genetic machinery
- reconstruct early earth conditions and see what happens
why are prokaryotes believed to have existed earlier than eukaryotes
appear earlier in fossil record, simpler, evidence eukaryotes evolved from prokaryotes
2 fundamental similarities between prokaryotes and eukaryotes that suggest life evolved once/eu from pro
- method of transcription and translation - suggests life evolved once
- all amino acids are laevo-rotatory and in nucleic acids sugars and dextro-rotatory - if you tried to make them chemically you’d get 50/50 split, in life one is selected for
what was produced when they recreated conditions of early earth in a lab
- amino acids - inc all biologically important ones
- purines and pyrimidines inc A,C,G,U - not T
- sugars
- porphyrins - forerunners of important compounds like vitamins and chlorophylls
- complex tar like substances - ??
what suggests life could have evolved elsewhere in space? note on rotatory forms
- chemicals created by early earth occur elsewhere in space
- but they have laevo and dextro rotatory forms, so have not been selected for by life
possible energy sources for life to evolve
- sun - uv radiation (less strong and harmful in ocean)
- radioactivity
- electric discharges - lightning
- volcanic - hot springs etc
origin of rna world theory
- what came 1st DNA or proteins?? both needed to make each other
- breakthrough - 1980s discovery of self splicing RNA
- uracil not thymine
RNA world theory - metabolic pathways that developed
- chemoautotrophs: energy from oxidising inorganic substances, c from co2
- chemoheterotrophs: energy and co2 from consuming organic compounds (can only get so far - needs to create)
- photoautotrophs: energy from light, c source co2
- photoheterotrophs: energy from light, c from consuming organic material
bacteria that photosynthasise
cyanobacteria
what does photosynthesis require
- synthesis of cytochromes - basis of o metabolism
- porphyrins - needed for chlorophyll
spectrum of organisms that are poisoned by o to can’t live w/o
- obligate anaerobes: poisoned by o2 and live exclusively by fermentation/anaerobic resp
- aerotolerant organisms: cant use o2 for growth, tolerate it, live by fermentation
- facultative anaerobes: use o2 of present but can live by fermentation
- obligate aerobes: use o2 for cellular resp, cant live w/o
