Oxygen Enrichment

Primordial Earth had a reducing atmosphere that contained very low levels of oxygen gas

After about ~2 billion years of prokaryotic life, a form of chlorophyll evolved in prokaryotes (forming cyanobacteria)

This allowed for the process of photosynthesis to occur, creating oxygen gas as a by-product via the photolysis of water

The increase in oxygen in the atmosphere was coupled to a number of significant effects:

  • There was a breakdown of chemicals in the atmosphere and oceans to produce oxidised compounds (e.g. CO2)
  • There was an evolution of organisms capable of breaking down oxygen-rich oxidising agents (e.g. aerobes)
  • The subsequent formation of an ozone layer restricted UV radiation to allow for the proliferation of a wider range of life forms

oxygen enrichment