Abiogenesis
Explains how cells came from non-living materials through abiogenic synthesis. Accumulation of organic compounds was possible when the Earth contained no O2. Simple non-living organic molecules got increasingly complex until they formed early life of prokaryotes.
Who demonstrated Abiogenesis
Miller and Urey
The Great Oxygenation Event (2.45 BYA)
Caused the first mass extinction of anaerobic cells as O2 was toxic. Cyanobacteria produced O2 through photosynthesis, and oxygen accumulated after iron rocks were saturated.
Ordovician Mass Extinction (+450 MYA)
Gamma rays from a nearby hypernova damaged the ozone layer, causing glaciation. Nitrogen and ozone formed nitrogen dioxide.
Permian-Triassic Extinction Event (250 MYA)
Volcanic eruptions lasting 2 million years killed ~95% marine and 75% land species. Vertebrate recovery took 30 million years.
Cretaceous-Paleogene Extinction (65 MYA)
Asteroid wiped out 3/4 of organisms. Ectotherms under 25kg survived best.
How did cells get constructed?
Earth's early atmosphere lacked O2, enabling organic molecule formation. RNA world theory suggests RNA molecules controlled replication and reactions. Protein synthesis and DNA came later. Cyanobacteria evolved photosynthesis, releasing O2.
Structure of Prokaryotic Cells
Tiny (1-10 µm), shapes: spherical, rod, spiral. Components include cell membrane, nucleoid (DNA), cytoplasm, cell wall, capsule, flagella, spores. Model organism: E. coli.