Origins and Evolution

Origins of Life

• Essential conditions for life:
  • Presence of essential elements for organic molecules.
  • Continuous energy source, mainly from the Sun.
  • Temperature range permitting liquid water.
• Prebiotic soup theory suggests life’s biomolecules arose from inorganic molecules.
• Early metabolism involved anaerobic oxidation-reduction reactions.
• Evidence: stromatolites (3.4 billion years old) and microfossils.

Elements of Life

• Major biomolecule elements formed through nuclear reactions in stars.
• Earth's composition: core, mantle (iron-rich), and crust (biosphere support).
• Volcanic activity produced the early atmosphere (primarily CO2).
• Cyanobacteria contributed to atmospheric oxygen (O2).

Geological Evidence for Early Life

• Biosignatures include geological records of life.
• The Hadean eon (4.6 to 4.0 Gyr ago) marked intense meteor bombardment.
• The Archaean eon (4.0-2.5 Gyr ago) shows evidence of microbial life (isotope ratios, stromatolites).

Banded Iron Formations (BIFs)

• Formed by iron oxidizing microorganisms.
• Evidence for fluctuating oxygen levels in early Earth's atmosphere.

Evolution: Phylogeny and Gene Transfer

• Clades: branching groups of related organisms (monophyletic group).
• Phylogeny: full description of organisms' divergence.
• Mechanisms of evolution: random mutations, natural selection, reductive evolution.
• Molecular clocks provide temporal information based on sequenced DNA.

Natural Selection and Adaptation

• Variants that survive reproduce due to natural selection.
• Adaptive evolution can be rapid under selective pressures.

Microbial Species and Taxonomy

• Prokaryotic species are challenging to define (asexual reproduction).
• Phylogeny and ecological niche are important for classification.
• Pangenomes consist of core and accessory genes, often with open configurations in nature.

Endosymbiosis

• Mitochondria and chloroplasts originated from endosymbionts.
• Mutalistic and parasitic relationships can drive evolution.
• Important for understanding bacterial infections in humans (e.g., filariasis due to nematodes carrying Wolbachia).

Conclusion

• Understanding early life and evolution involves addressing unresolved questions about conditions, temperatures, and the origins of first cells.