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 chronology4. 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 lifeDNA based

Evidence or reasoning

DNA sequencing

2. Establishing a list of events

Assumed stepsDarwin’s warm little pond

Common ancestor to all modern lifeDNA based

Evidence or reasoningOparin 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 stepsDarwin’s warm little pond

Common ancestor to all modern lifeDNA based

Evidence or reasoningOparin 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 modernorganisms are hyperthermophilesHowever, rapid decay of most organic molecules at high temperatures makes this unlikely for the pond.

2. Establishing a list of events

Assumed stepsDarwin’s warm little pond

Appearance of anaerobic heterotrophs using surrounding molecules for growth and reproduction

Common ancestor to all modern lifeDNA based

Evidence or reasoning

Heterotrophs chemically simple, butneed 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

2. Establishing a list of events

Assumed stepsDarwin’s warm little pond

Appearance of anaerobic heterotrophs using surrounding molecules for growth and reproduction

Transition to RNA world

Common ancestor to all modern lifeDNA based

Evidence or reasoning

RNA is catalytic and encoding. Used in primitive reproduction today.

2. Establishing a list of events

Assumed stepsDarwin’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 lifeDNA based

Evidence or reasoning

This is what we see today. Better fidelity of information carriage

2. Establishing a list of events

Assumed stepsDarwin’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 lifeDNA based

Evidence or reasoning

Margulis minimum cell.

2. Establishing a list of events

Assumed stepsDarwin’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 lifeDNA based

Evidence or reasoning

Necessary for sustainability. Most primitive life does it.

2. Establishing a list of events

Assumed stepsDarwin’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 lifeDNA based

Evidence or reasoning

All molecular trees show a single, common root to the tree of life.

3. Establishing a possible chronology

Assumed stepsDarwin’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 lifeDNA based

Evidence or reasoningDuring and after meteorite bombardment. Murchison Meteorite - 4.6 GaAfter 3.8 Ga

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Carbon isotopes go light very early - around 3.8 Ba. Stromatolites.(Oldest fossils disputed, oldest definite fossils 2.5 Ba from Transvaal Supergroup)

3. Establishing a possible chronology

4. Archaean life

Lecture 2: Proterozoic lifeand metazoans

1. Prokaryotes and eukaryotes2. Evolution of eukaryotes

3. Eukaryote radiations4. Evolution of metazoans

5. PreCambrian-Cambrian boundary

1. Prokaryotes and eukaryotes

2. Evolution of eukaryotes

3. Eukaryotic radiationsBiologically: probably split off at 3.5 BaPalaeontologically: oldest ?2.1 Ba from Michigan BIF

large cells common since 2 BaAcritarchs: unequivocal eukaryotes, probably dinoflagellate cysts

from 1.7 Ba common from 1 Ba

4. Origin of metazoans

4. Origin of metazoans

5. The PreCambrian-Cambrian boundary

5. The PreCambrian-Cambrian boundary