Early Evolution of Earth: Chronology of Events

Early Evolution of Earth: Chronology of Events

• 4.6 – 4.5 Ga – Accretion of earth from solar nebula

• 4.5 - 4.2 Ga – Heating of protoearth from isotopic decay, gravitational
collapse, and meteorite bombardment (amplified by super greenhouse
effect) causing melting, differentiation of mantle and core, and
outgassing.

• 4.2 - 4.0 Ga – First crustal rocks formed. Differentiation of oceanic and
continental crust begins through recycling. Continued degassing.
Large meteorite impacts periodically removing protoatmosphere.

• 3.9 Ga – Decline in meteorite bombardment as loose nebular debris is
captured by Sun and planets. First stable continental crust forms.

• 3.8 - 3.5 Ga – Buildup of crustal material into protocontinents.
Accretion of continents via microplate tectonics. Water condensing
and accumulating above basaltic crust, causing sedimentation and
potentially life.

• 3.0 Ga - Beginning of oxygenation of atmosphere due to photochemical
dissociation and photosynthesis (BIF).

• 2.4 - 2.2 Ga – Free oxygen buildup in atmosphere and oxidation of earth
surface.