1. Geology 1: Palaeontology Lecture 1: Origin of life 1. How to study origins 2. What is life? Categories of living organisms What life requires and produces 3. The evidence for origins 4. A narrative of early evolution 5. Evolution of more complicated life forms

2. 1. How to study the origin of life Interaction with atmosphere Grades of organisation - simplest modern life What life needs Fossils = likely narrative + likely chronology

3. 2.1 What is life ? Living systems can - 1. Fight entropy - be complex and highly organised 2. Be homeostatic - survive over a period of time 3. Take energy from the environment 4. Respond to external stimuli 5. Reproduce - transmit information between generations - evolve and adapt.

4. 2.2 Types of life 1. Multicelled animals (metazoans) 2. Multicelled plants 3. Eukaryotes 4. Prokaryotes 5. A hypothetical minimum cell 6. Replicating molecules

5. 2.3 What life needs Carbon Liquid water Energy Phosphorus 2.4 What life produces CO 2 O 2 12 C enrichment in rocks Body fossils

6. 3.1 Evidence for origins - geology A. After 4.55 Ba B. After 4 Ba C. Before oldest fossils at 3.5 Ba D. ?Before oldest sediments at 3.8 Ba Earth forms Meteorites subside

7. 3.2 Evidence from 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

8. 3.3 Evidence from the atmosphere 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

9. 4. 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