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.