Early history of life W4 Flashcards
ppl used to think preecambrian
used to think there were no fossils/ evidence of life in this time, that’s why so long
the earliest part of Earth’s history, set before the current Phanerozoic Eon
Hadean
time period with no geological record
Early earth
moon was closer so shorter days, huge tides
land cover, no vegetation
low to no oxygen
more active volcanos, hotter
volcanic degassing
volcanic degassing
CO2, CH4, N2, H2O, H2S
• reducing atmosphere + oceans
?+cometary input
photlysis
• H2OàO à oxidises CH4 to CO2 + H2 lost
trace gases washed into ocean
NH3, CO, + nitrates, nitric acid, cycanide (HCN)
early earth geological evidence
recambrian rocks often well perserved, ex Australia (not covered)
however many have been modified
Precambrian rocks in‘shield’ areas - granitic igneous and metamorphic rocks; few sediments
when did life originate
4.1-3.8 Ga
Stromatolites
stromatolites are layered structures formed by the actions of cyanobacteria
biogenic structures, formed by life
so in a way they ar etrace fossils left by microbial organisms
proving bacteria authetinicty
age must be correct
microfossil must be indigenous to the rock
microfossil must be contemporaneous with the rock
microfossil must have proven biogenicity
anarobic life
does not use O2 for respiration
prokariotic life dominated for
ca 2Ga
Heterotrophs
consumers
methanogenic bacteria: CH3COOH → CH4 + CO2
anaerobic respiration - fermentation abiotic organic molecules
Autotrophs
producers
green and purple sulphur bacteria: CO2+ 2H2S → CH2O + 2S + H2O
modern anaerobic bacteria - anoxygenic photosynthesis solar radiation
O2 would have been toxic to these photosynthesising fermenters
Key steps early life
bacterial mats common and widespread (3.5-0.5 Ga)
appearance of oxygenic photosynthesis (cyanobacteria) between 2.5-3.8 Ga
6CO2 + 6H2O → C6H12O6 + nO2
appearance of aerobic respiration ~2.0 Ga
C6H12O6 + 6O2 ® 6CO2 + 6H2O
NB. aerobic respiration ~20x more efficient
as soon as oxygen available more effiecient, larger growth etc.
oxygenation proven through
banded iron formation
redox sensitive elements or minerals
ferrous iron Fe2+ soluble oxidized to ferric iron Fe3+ insoluble
bands form bcs sunlight varies due to seasons, oxygen prod. varies
redbeds on land
at some point all fe 2+ oxidized and sentimented out → iron all oxidized → oxygen from ocean to atmosphere bcs sink into ocean disappeared
then oxidization of terrestrial records ex. Redbeds on land
Eukaryotes
cells with nuklei about 1.6
Linnean Binomial System
Kingdom → Phylum (Stamm) → Class → Order → Family → Genius → Species
Biological Nomenclature
A species is identified by both its genus name and specific epithet
example: Panthera pardus (Linnaeus 1758)
Panthera = genus name, capitalized !!
pardus = specific epithe, not capitalized !!
Species def
A group of individuals that interbreed or have potential to interbreed and that do not interbreed with other interbreeding groups
