Archean Eon – Simple Life Emerges

Key Events

  • Earth’s continents start to form.
  • Simple life emerges in shallow water.
  • The earliest microbial fossils from bio-sedimentary structures called stromatolites and hydrothermal systems have been found in Australia, South Africa and Canada.
  • The ‘Late Heavy Bombardment’ lasts from the end of the Hadean Eon until 3,800 million years ago. Earth, the Moon and the other planets are pummelled by asteroids and comets, whose orbits become unstable.
Copyright: Vix Southgate

Facts, Debates & Trivia

  • The eon is named after the Greek word for ‘beginning’.
  • Conditions on Mars may have been suitable for life around this time (4,100-3,000 million years ago). NASA’s Perseverance rover is collecting rocks that may hold evidence of ancient life on Mars. These samples will be brought back to Earth for analysis in the 2030s. 
  • Studying organic hazes in the atmosphere of Saturn’s largest moon, Titan, may help reveal how the chemical building blocks for life emerged in the early Earth’s atmosphere.
The Archean Eon is the second point in the Earth Story Trail.
The Archean Eon is the second point in the Earth Story Trail. Credit: A Heward/Cornwall Sea to Stars


  • Temperatures on Earth are similar to the present day. Although the Sun has only ~75-80% of its current luminosity, a thick atmosphere traps in Earth’s heat.
  • The oxygen-free atmosphere produces a ‘reducing environment’ with abundant methane, carbon dioxide, sulphur and nitrogen compounds. 
The Archean Earth may have been covered by a hazy orange atmosphere, similar to Titan. Credit: NASA-GSFC/F Reddy.


4,000-2,500 million years ago

(1,500 million years)

1 metre = 
20 million years

Where have you reached on the trail?