4/ origins of prokaryotes and eukaryotes Flashcards
how do fossil stromatolites provide evidence for prokaryotic life
- these are layered fossils formed by earliest prokaryotes on earth - likely cyanobacteria
- formed in sharks bay Australia and red sea, where water too salty for life to eat the goo
how do fossil microorganisms (silicified in cherts) provide evidence for early life
- water between rocks squeezed out into nodules where fossils often formed - we see bacteria
when did the atmosphere turn from anaerobic to aerobic
2000 Ma
how do fossil microorganisms (resistant cell walls) provide evidence for prok life
- resistant cell walls (inorganic sheath) called acritarchs preserved in siltstones
what 3 ways do rocks hold fossils that are evidence for prok life
- fossil stromatolites
- fossil microorganisms - cherts and acritarchs
- carbonaceous matter that can be identified chemically as the product of ancient life - rubisco prefers carbon 12, more carbon 12=more life
for how long did prokaryotes dominate the planet
2 billion yrs
by what year is there advanced prokaryotic life in the oceans, what was this consisting of
- 3500 Ma
- stromatolites on floors of shallow seas and free living prokaryotes floating around oceans
- both inc autotropic cyanobacteria which produce o as biproduct of their photosynthetic metabolism and heterotrophic consumers that sweep up waste products
3 early oxygen sinks
- volcanic gases in the atmosphere combines w o2
- dissolved iron scavenged o2 to form BIFs
- microorganisms carrying out aer resp
what does the presence of iron pyrite/fools gold suggest about the atmosphere at that time
- no oxygen
when did red beds form, what are they, what do they suggest
- 2000 Ma
- quartz w layer of iron oxide - oxygen present
- red beds sinks for excess oxygen
1st evidence of eukaryotes, when and what
- 2 bil yrs ago
- some acritrachs big enough to suggest they were euk
when was the great oxygenation event, before and after, what occurs at same time
- 2.4 bil - 1.8 bil yrs ago
- started to be built up then disappeared. by end permanently oxygenated
- coincident w Huronian ice age caused by elimination of atmospheric methane by GOE
symbiosis theory for how euk originated, developments
- proto eukaryote engulfs thermoplasma /prok
elaboration of cell memb theory for euk development
- prok memb folds in on itself
- becomes obligate, forms nucleus
what theory for euk development is now most widely supported
- multiple symbiotic events
- allowed: mitochondria, chloroplasts, flagella and cilia and maybe mitosis (allowed centrioles)
- cells that couldn’t cope w o allowed themselves to be engulfed
- mechanisms that allow themselves to be separated off when cell divides
- chloroplasts have own dna similar to cyanobacteria
symbiotic origin of flagella and cilia
- spirochaete bacteria
- have basal bodies sunk into cell walls - divides when cell divides
- basal body potentially ahs rna
- proto cell took on prok to allow movement
- mitosis too?
