Great Oxidation Event

Question 1

How did the early Earth form?

Answer 1

-formed after collision with mars-sized planet called Theia + continually bombarding of meteorites at 4.5 bya/Ga (proterozoic)

Question 2

What was the early earth called and why?

Answer 2

-hadean earth
-hades (hell-like)

Question 3

After the hadean earth, what process occured to produce our core, mantle, and crust?

Answer 3

-earth was really hot so iron and nickel melted and sank to the middle due to gravity to produce the core
-lighter silciates floated to the top = this formed mantle and crust
-this process is called differentiation

Question 4

after the earth differentiated and cooled below 1000 C, what formed? what type of landmass?

Answer 4

-rocks formed and landmass was mostly low-lying volcanic islands like hawaii; these rocks were ultramafic lavas called komatiites

Question 5

even with the landmass, earth was mostly covered with what? coupled to this, we were able to date which type of rocks to the hadean earth?

Answer 5

-water
-sedimentary (3.9-3.8 by)

Question 6

what was the atmosphere of early earth like? what were the effect of these gases on the environment?

Answer 6

-it had high CO2 and methane, no atmospheric O2, not ozone layer
-high temperature reaching 90C, really hot, lack of ozone layer means that there was no protection from UV radiation
-rain was highly acidic because of richness of acids -> chemical weathering

Question 7

origin of life: what is the organic soup model?

Answer 7

monomers where formed by reduced gases in atmosphere + UV radiation -> could form amino acids

Question 8

origin of life: what are the two ways that meteorites are hypothesized to play a role in the development of life?

Answer 8

-shock waves from entry into atmosphere formed shock waves that make a.a monomers form gases
-panspermia: comets carry organic compounds for life or actually life

Question 9

the meteorites and organic soup models have been rejected for what reason?

Answer 9

difficult to form polymers in ocean due to monomer disperion

Question 10

problem with shockwave and organic soup model is what?

Answer 10

CO2 acts as greenhouse, so atmosphere is not as reducing

Question 11

the open ocean models for origin of life was problematic and the solution proposed was what?

Answer 11

evaporation of monomers lead to polymerization

Question 12

last and most plausible start for origin of life?

Answer 12

reduced gases emitted at hydrothermal vents reacts with oxidizing seawater to form organic compounds and minerals are the templates of polymerization

Question 13

what is the period of late heavy bombardment?

Answer 13

-happened 4.1-3.8 bya
-weakens organic soup model cause vaporized H20 would have sterilize the planet for years

Question 14

life likely arouse in sheltered environemtn free from bombardments like what?

Answer 14

diffuse vents, black smokers associated with mid-ocean ridges

Question 15

the oldest organisisms that we know of are what?

Answer 15

associated with growth in hot water, thermophilic prokaryotes

Question 16

earliest cells used which chemical materials?

Answer 16

-sulfur
-methane (methanogenic bacteria in deep sea vent)

Question 17

what are 4 evidences of archean life?

Answer 17

-microfossils
-biogenic structures (stromatolities and MISS)
-isotopes
-biomarkers

Question 18

MISS stands for what? what are them?

Answer 18

-microbially induced sedimentary structures
-structures formed by microbial mats of filamentous bacteria trapped in sediments in tidal flat settings

Question 19

how do isotopes indicate life?

Answer 19

photosyn. takes in C12 and eriches C13 in environments
C13 (+) = low C12
C13 (-) = high C12 (photosynthesis)
-20 = biological (from photosynthesis)
-40 = from methanotrophic bacteria

Question 20

type of photsynthesis

Answer 20

oxygenic and anoxygenic

Question 21

when does cyanobacteria formed?

Answer 21

3.5- 2.7 bya

Question 22

though cyanobacteria evolved earlier, GOE happened when?

Answer 22

2.5 bya

Question 23

Proxies supporting timing of GOE

Answer 23

-red beds
-pyrite
-decreasing in 33S isotope (only produced in absence of oxygen)
-manganese ore
-banded iron formation (BIF)

Question 24

what was the lomagundi event?

Answer 24

long lasting peak of C13 isotopes during GOE; photosynthesis take in C12 (environment enriched in C13)

Question 25

BIF despite forming in shallow platforms, source of iron is what? iron is oxidized by what?

Answer 25

-deep hydrothermal vents
-oxygenic or anoygenic photosynthesis (both biological)

Question 26

How did NI depletion lead to GOE?

Answer 26

early earth rick in Ni and then earth cools so [Ni] decrease= starvation of methanotrophs = lower [methane] = increase [oxygen]

Question 27

increasing landmass contribution to GOE

Answer 27

allowed for Cyanobacteria and stromalites to grow

Question 28

what is the connection between pyrite oxidation and GOE?

Answer 28

oxidation = increasing acid which dissolves Cr which becomes part of BIF

Question 29

What prevented O2 accumulation before GOE?

Answer 29

-cyanobacteria were starved (low phosphate)
-dissolved iron was toxic to cyanobacteria
-many reductants that oxygen reached with first
-not enough landmass for cyanobacteria growth

Question 30

increase in oxygen and formation of ozone had which consequences?

Answer 30

-plankton growth in ocean
-biofilms conquered land = increase weathering
-euk diversification

Question 31

life in proterozoic

Answer 31

-thrombolities
-gunflint chert (BIF which microfossils)
-algae

Question 32

euk seen in fossils record at what time?

Answer 32

1.9bya (grypania)
1.2 (red algae)

Question 33

what are acritarchs?

Answer 33

organic-walled microfossils of unknown biological affinity, but with features interpreted as eukaryotic