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G4 Earth Evolution: Life Lecture 1: Origin of life and complex life. Myth marketing and hype. Lecture 2: Proterozoic life and metazoans Lecture 3: The Phanerozoic record and exceptional preservation Lecture 4: Effects of life on Earth and non-Uniformitarianism.
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G4 Earth Evolution: Life Lecture 1: Origin of life and complex life. Myth marketing and hype. Lecture 2: Proterozoic life and metazoans Lecture 3: The Phanerozoic record and exceptional preservation Lecture 4: Effects of life on Earth and non-Uniformitarianism
Lecture 1: Origin of life and complex life. Myth marketing and hype. 1. What can be known about the evolution of life? 2. Establishing a list of events 3. Establishing a possible chronology 4. Archaean life 5. Evolution of complexity
1. What can be known about the evolution of life? Lazcano, 2001 ‘Of necessity, work on the origin of life should be regarded as enquiring and explanatory rather than definitive and conclusive ….the issue should be addressed conjecturally in an attempt to construct a coherent historical narrative.’ Hence influenced by scientific and cultural fashions, for example, the possibility of life originating on Mars early heterotrophy in a ‘Dog-eat-Dog’ social climate. Is a scientist allowed to not know something?
2. Establishing a list of events Assumed steps Common ancestor to all modern life DNA based Evidence or reasoning DNA sequencing
2. Establishing a list of events Assumed steps Darwin’s warm little pond Common ancestor to all modern life DNA based Evidence or reasoning Oparin and Haldane’s theories, 1920’s Miller experiments (eg 1993) - electrical discharges for 1 week over a mixture of CH4, NH3, H2 and H2O produced organic molecules including amino acids and urea. Importance of HCN - polymers denature to produce amino acids, purines, and adenine. Evidence from the Murchison Meteorite - 4.6 Ga, includes array of protein and non-protein amino acids, purines, pyramidines, hydrocarbons and evidence of liquid water.
2. Establishing a list of events Assumed steps Darwin’s warm little pond Common ancestor to all modern life DNA based Evidence or reasoning Oparin and Haldane’s theories, 1920’s Miller experiments (eg 1993) - electrical discharges for 1 week over a mixture of CH4, NH3, H2 and H2O produced organic molecules including amino acids and urea. Importance of HCN - polymers denature to produce amino acids, purines, and adenine. Evidence from the Murchison Meteorite - 4.6 Ga, includes array of protein and non-protein amino acids, purines, pyramidines, hydrocarbons and evidence of liquid water. Most primitive modern organisms are hyperthermophiles However, rapid decay of most organic molecules at high temperatures makes this unlikely for the pond.
2. Establishing a list of events Assumed steps Darwin’s warm little pond Appearance of anaerobic heterotrophs using surrounding molecules for growth and reproduction Common ancestor to all modern life DNA based Evidence or reasoning Heterotrophs chemically simple, but need a convincing method of carrying information through time. RNA? But ribose and phosphate esters chemically unlikely in chemical soup. Maybe modified nucleic acid sugar-phosphate backbones , maybe another self-replicating molecule, maybe something like prions.
2. Establishing a list of events Assumed steps Darwin’s warm little pond Appearance of anaerobic heterotrophs using surrounding molecules for growth and reproduction Transition to RNA world Common ancestor to all modern life DNA based Evidence or reasoning RNA is catalytic and encoding. Used in primitive reproduction today.
2. Establishing a list of events Assumed steps Darwin’s warm little pond Appearance of anaerobic heterotrophs using surrounding molecules for growth and reproduction Transition to RNA world Darwinian evolution towards dominance of DNA Common ancestor to all modern life DNA based Evidence or reasoning This is what we see today. Better fidelity of information carriage
2. Establishing a list of events Assumed steps Darwin’s warm little pond Appearance of anaerobic heterotrophs using surrounding molecules for growth and reproduction Transition to RNA world Darwinian evolution towards dominance of DNA Evolution of primitive cells Common ancestor to all modern life DNA based Evidence or reasoning Margulis minimum cell.
2. Establishing a list of events Assumed steps Darwin’s warm little pond Appearance of anaerobic heterotrophs using surrounding molecules for growth and reproduction Transition to RNA world Darwinian evolution towards dominance of DNA Evolution of primitive cells Evolution of autotrophy Common ancestor to all modern life DNA based Evidence or reasoning Necessary for sustainability. Most primitive life does it.
2. Establishing a list of events Assumed steps Darwin’s warm little pond Appearance of anaerobic heterotrophs using surrounding molecules for growth and reproduction Transition to RNA world Darwinian evolution towards dominance of DNA Evolution of primitive cells Evolution of autotrophy Common ancestor to all modern life DNA based Evidence or reasoning All molecular trees show a single, common root to the tree of life.
3. Establishing a possible chronology Assumed steps Darwin’s warm little pond Appearance of anaerobic heterotrophs using surrounding molecules for growth and reproduction Transition to RNA world Darwinian evolution towards dominance of DNA Evolution of primitive cells Evolution of autotrophy Common ancestor to all modern life DNA based Evidence or reasoning During and after meteorite bombardment. Murchison Meteorite - 4.6 Ga After 3.8 Ga ………. ……….. ………. Carbon isotopes go light very early - around 3.8 Ba. Stromatolites. (Oldest fossils disputed, oldest definite fossils 2.5 Ba from Transvaal Supergroup)
Lecture 2: Proterozoic life and metazoans 1. Prokaryotes and eukaryotes 2. Evolution of eukaryotes 3. Eukaryote radiations 4. Evolution of metazoans 5. PreCambrian-Cambrian boundary
3. Eukaryotic radiations Biologically: probably split off at 3.5 Ba Palaeontologically: oldest ?2.1 Ba from Michigan BIF large cells common since 2 Ba Acritarchs: unequivocal eukaryotes, probably dinoflagellate cysts from 1.7 Ba common from 1 Ba
