Easy Science: simple timeline of pre-Cambrian earth and life

Understanding the formation of the earth can be overwhelming. I've simplified and condensed the big events into an easy-to-follow timeline. Obviously, the list is not meant to be exhaustive and probably isn't 100% accurate. Clicking on the links will take you to Wikipedia that lead to journal articles (a few links directly to sources).

Pre-Earth: The universe starts with the Big Bang 13.8 billion years ago.

Earth

• Hot Earth: earth covered in molten rock
  

  Zircon crystal.

  • 4.6 bya: halo of debris (from Big Bang) around sun
    • Particles collide to form larger masses until spheroid planets form
  • 4.5 bya: Mars-sized planet Thea collides with Earth then becomes moon
    • Moon 10x closer + shorter days (earth rotating faster) = lava tidal waves every 6 hours?
  • 4.4 bya: some crust (evidence: Zircon crystal)
• Cool Earth
  • 4.3 bya: lots of crust, oceans [disputed]
    

    Late Heavy Bombardment.

    • Seafloor basalts metamorphosed by 16 km burial pressure
  • 4.0~3.8 bya: Late Heavy Bombardment
  • 4.0 bya: lots of crust (Canadian gneiss)
    1. At first, surface of earth so hat that lava stays molten at surface
    2. Eventually, earth cools; rafts form
    3. Ultramafic crust develops; ultramafic eruptions occurring; mantle composition not changing
    4. Surface temperature drops; crust gets thicker; ultramafic magma gets trapped; cools, fractionalizes; mafic eruptions
    5. Plates form, cool subduct; flux melting causes felsic eruptions
  • 3.8 bya: oceans
  • 2.3 bya: Great Oxidation Event

Life

• Prokaryotes
  • 4.3 bya: Light carbon (C12) diamond inclusion in Jack Hills, Australia [disputed]
    • Believed that photosynthesis is the only way to produce C12, but other processes have been discovered
  • 3.5 bya: Cyanobacteria fossil in Apex Chert, Australia [disputed]
    • Chert embedded in volcanic rocks where cyanobacteria might not live; could be inorganic erosional features (microcracks), which have been found in other chert
  • 3.2 bya: Stromatolites in Pilbara, Australia
• Eukaryotes
  

  Bangiomorpha fossils from Butterfield (2000).

  • 2.7 bya: Steranes in Pilbara, Australia [disputed]
    • Steranes only produced by eukaryote metabolism; possible contamination of sample
  • 2.1 bya: Grypania in Michigan, USA [disputed]
  • 2.0 bya: Chuaria in Jixan, China [disputed]
  • 1.2 bya: Bangiomorpha in Canada

The material came from my lecture notes for EOS 204L, Duke University, Spring 2014, and is not necessarily accurate or up-to-date.

Click here or here for interactive timelines of Earth's history.