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Lecture 3: The early earth and the origin of life 1. What was the early earth like? 2. Could it sustain life? 3. When could life have evolved? 4. Indirect evidence for life 5. The oldest fossils 6. Biotic effects on surface processes Lecture 3: The early earth and the origin of life 1. What was the early earth like? Evidence for the early environment ripples pillow lava Banded Iron Formation pyrite conglomerate detrital pyrite Lecture 3: The early earth and the origin of life 2. Could it sustain life? The chemistry of early life The locus for the origin of life is unknown. However, biochemistry closely mirrors the solubility of elements in seawater Common to both are: Na, K, Mg, Ca S, C, N, P The metabolism of early life HETEROTROPHY Anaerobic fermentation (primitive) glucose ->pyruvate -> ethyl alcohol + CO2 + heat +2 energy Aerobic respiration (advanced) glucose -> pyruvate -> H2O+CO2+heat + 36 units energy AUTOTROPHY Anoxic photosynthesis (primitive) CO2 + H2S -> glucose + S Oxygenated photosynthesis (advanced) CO2 + H2O -> glucose + oxygen Lecture 3: The early earth and the origin of life 3. When could life have evolved? When did life evolve? After 4.6 Ba, when Earth formed After 4.0 Ba, when meteorite bombardment stopped After liquid water, recorded in oldest sediments, 3.8Ba Before isotopic fractionation of carbon by RUBISCO Before oldest fossils, 3.5 Ba Types of life 1. Multicelled animals (metazoans) 3. Eukaryotes 5. A hypothetical minimum cell 2. Multicelled plants 4. Prokaryotes 6. Replicating molecules How to study the origin of life Interaction with atmosphere Grades of organisation - simplest modern life What life needs Fossils = likely narrative + likely chronology Prokaryote Small, usually anaerobic metabolism, protected from UV, short life Eukaryote Large, aerobic, damaged by UV, longer life The phylogeny of early life Lecture 3: The early earth and the origin of life 4. Indirect evidence for life Indirect evidence for life A. Evidence for O2 Banded iron formations 3.5-1.8 By Pyrite conglomerates 2.8 - 2.0 By B. For photosynthesis Isotopically ‘light’ carbon (more carbon-12 than would be expected in abiotic situation) Isua rocks slightly light (3.8 Ba) All carbonates < 3.5 Ba very light Lecture 3: The early earth and the origin of life 5. The oldest fossils The oldest fossils Oldest fossils 3.5 Ba (for last decade) 1. Onverwacht Group (Swaziland Supergroup), South Africa 2. Warrawoona Group (Pilbara Supergroup), Western Australia Cell chain Stromatolites Both Prokaryotes Nb Biological evidence suggests split between prokaryotes and eukaryotes at about 3.8 Ba Early fossils: stromatolites Living prokaryotes Precambrian prokaryotes Lecture 3: The early earth and the origin of life 6. Biotic effects on surface processes CO2 reservoirs for long timescales Carbonate carbon Burial Organic carbon Weathering Land Atmosphere 750 biotaWarm surface ocean Cold surface ocean 850 550 150 Soils andIntermediate and deep waters 38000 detritus Weathering 1500 Time, O2, rocks and life O2 and ozone shield as Fe runs out Fe absorbs O2 Time, O2, rocks and life Eukaryotes Prokaryotes Narrative of origin and evolution of life Ba 4.55 Earth forms 4.00 Meteorites subside molecules replicate minimum cell appears photosynthetic prokaryotes 3.8 Oldest sediments limited diversification 3.5 Oldest fossils prokaryotes dominate eukaryotes rare 2.1 Oldest large cell - subject of next lecture