great oxidation event! Flashcards
what was the temperatures of earth before life?
hot
what did the earth look like before life
hardly any land
submerged
what was happening to the atmosphere before life?
atmosphere reducing (oxidation is prevented by removal of oxygen and other oxidizing gases or vapours)
- no O2
what happens if there is no free atmospheric O2?
no ozone (protect from harsh UV rays)
mostly methane, CO2 dropped
what was the oldest continent?
ultramafic rocks called komatites
what is the oldest rock?
acasta gneiss
sedimentary
what was the rain like before life?
acidic, caused chemical weathering
what are some of the likely scenarios, organisms that would have been first to evolve
earliest cells may have used sulfur or methane
cyanobacteria: first organism that used oxygenic photosynthesis because they produce O2
know the four indicators of evidence for archean life
- microfossils
- biogenic structure (stromatolites and Microbially Induced Sedimentary Structures)
- isotopes (negative carbon: inorganic to organic
- biomarkers
four things to look for in ancient life?
- satellite image of chlorophyll: more chlorophyll, more photosynthesis
- arctic, mouth of rivers and coastal settings have high amount of chlorophyll
- primary productivity: where you have the most of it (more nutrients, more productivity) is close to land
- cyanobacteria learned how to split water to form O2
microfossils: what are they what is the problem?
the tiny remains of bacteria, protists, fungi, animals, and plants
too tiny to be seen with naked eye, hard to study
stromatolites: what are they, who made them
layered deposit, mainly of limestone, formed by the growth of blue-green algae by trapping, binding and sedimentation of sedimentary rocks
microbial reefs creates by cyanobacteria
isotopes: why carbon isotopes are useful, what is the problem with carbon isotopes
negative carbon isotopes indicate life (carbon 12 inorganic turns into organic carbon 13)
kicked out methane producing bacteria
what is a biomarker? issues with using biomarkers?
organic compound derived from more complex precursors (a footprint)
timing is critical, expensive, storage / longevity of the sample
when is the great oxidation event??
2.5 billion years ago
low O2 prior, then it ramped up
what is the smoking gun for the great oxidation event?
sulfur isotopes
- only generate in absence of oxygen
- oxygen cause no UV from coming in, no sulfur 33 forming, oxygen around
- sulfur 33 in, oxygen not around
what is a red bed
rusty rock
- made red by iron (rust)
- red means you know it has oxygen
what is a green bed
no O2
what is evidence for oxidation?
- red bed
- geological time
- paleosol: old soil (red shows oxygen)
- pyrite: conglomerate (formed in a river, rounding = particle bashing), not stable in presence of oxygen, oxidizes to rust
- iron can have several oxidation states (- +2 –> +3 = oxidized; reduced: no O2; oxidized: O2)
- manganese: only mag4 formed in presence of O2 (black if O2 present)
- sulfur: 33 sulfur (UV reacts with sulfur dioxide in the presence of O2), most convincing for when there was and was no oxygen
what is a banded iron formation?
- made up of iron and silica
- formed at an early time
- these rocks are chemical sediment ex. salt
- classic sediment: sand, silt, slay
- can form in two ways (1. reaction of O2, cyanobacteria 2. anoxygenic)
- we must have had plankton through time - indicates we had sea life for millions of years, and they began to oxidize iron out
- only after iron is out of the ocean could O2 accumulate in the atmosphere
what does the nickel record tell us? why important
- nickel concentration: nickel is high at 2.7 million years ago, and then it drops off significantly
- decline -> phanogens starve, no methane in atmosphere, oxygen accumulate
what is chromium record? why is it important
peak -> dissolve chromium from land to oceans, acid from O2 in atmosphere on land, oxidized from pyrite
cyanobacteria developed early on. why does it take 500 million years for oxygen to accumulate
- nutrients: key nutrients like phosphorous, very little weathering, bacteria were nutrient winded (not enough)
- do not like high iron/ posioned by iron: had to wait for all of the iron to get cleared out (toxic)
- lots of reduced things that take a long time to get rid of before O2 can come in (reduced gas)
- not a lot of shallow water / not enough land above sea level - circumference around the land is very small as compared to the whole proportion of the earth (less continents exposed)
O2 in atmosphere? what does it mean for life
- microbrial: bacteria, early algae, acritarchs
- producing things that are now identifiable
- create ozone screen: now, incoming UV radiation gets filtered out
bacteria that is unable to be seen is called?
microscopic
bacteria that is able to be seen is?
macroscopic
lots of carbon 12
+carbon12
no carbon 13
-carbon13
what sign shows it is likely photosynthetic?
(-)
what is the story for the formation of nickel concentration
- earth was hotter earlier on (over 15000 degrees)
- crust is silicone rich
- more melting of the mantle
- components out of volcanos had a lot of nickel
- nickel would have affected microbe bacteria at that time
- before 2.5, the atmosphere was composed of methane and CO2
- methane producing bacteria need nickel
- nickel drops because of cooling
- makes organisms that need nickel die off
- organisms that need oxygen are able to evolve
the more positive carbon 13 present means there is more or less carbon 12?
less!
how did chromium accumulate step by step?
- chromium does not dissolve easily, they just sit there
- mobilize with lots of oxygen or very acidic conditions
- either at 2.5, there was lots of oxygen or it was very acidic in order for there to be a chromium spike
- pyrite in water, will pool and create acid
- bacteria grows in pyrite that love low pH / very acidic conditions
how does the trend in chromium content occur
pyrite is now reactive due to oxygen, makes it acidic, kills off chromium
