Early history of life W4

Question 1

ppl used to think preecambrian

Answer 1

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

Question 2

Hadean

Answer 2

time period with no geological record

Question 3

Early earth

Answer 3

moon was closer so shorter days, huge tides
land cover, no vegetation
low to no oxygen
more active volcanos, hotter

Question 4

volcanic degassing

Answer 4

volcanic degassing
CO2, CH4, N2, H2O, H2S
• reducing atmosphere + oceans
?+cometary input

Question 5

photlysis

Answer 5

• H2OàO à oxidises CH4 to CO2 + H2 lost

Question 6

trace gases washed into ocean

Answer 6

NH3, CO, + nitrates, nitric acid, cycanide (HCN)

Question 7

early earth geological evidence

Answer 7

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

Question 8

when did life originate

Answer 8

4.1-3.8 Ga

Question 9

Stromatolites

Answer 9

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

Question 10

proving bacteria authetinicty

Answer 10

age must be correct
microfossil must be indigenous to the rock
microfossil must be contemporaneous with the rock
microfossil must have proven biogenicity

Question 11

anarobic life

Answer 11

does not use O2 for respiration

Question 12

prokariotic life dominated for

Answer 12

ca 2Ga

Question 13

Heterotrophs

Answer 13

consumers
methanogenic bacteria: CH3COOH → CH4 + CO2
anaerobic respiration - fermentation abiotic organic molecules

Question 14

Autotrophs

Answer 14

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

Question 15

Key steps early life

Answer 15

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.

Question 16

oxygenation proven through

Answer 16

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

Question 17

redbeds on land

Answer 17

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

Question 18

Eukaryotes

Answer 18

cells with nuklei about 1.6

Question 19

Linnean Binomial System

Answer 19

Kingdom → Phylum (Stamm) → Class → Order → Family → Genius → Species

Question 20

Biological Nomenclature

Answer 20

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 !!

Question 21

Species def

Answer 21

A group of individuals that interbreed or have potential to interbreed and that do not interbreed with other interbreeding groups