Overview - Timescale, Physical Landscapes

The Archean Eon is the dawn of the geological record and is named after its beginning. Primordial seas and atmospheres originated in the Archean landscape and the earliest fossils have been identified.

• 4 - 2.5 bn
  
• Division of Precambrian Superon
  
• Earth's Dawn of primitive life and identified compounds
  

Rodinia - 1.3 - 0.9 bn

Landscape Development
In Archean, most Archean rocks are igneous due to the semi-continuous formation of oceanic and island arc crust over a period of 1.5 billion years.

• The oldest known rock on Earth, a 4.28 billion-year-old amphibolite volcanic deposit, is estimated to be found in the Nuvvuagittuq greenstone belt in Quebec, Canada.
  
• Then, as now, iron was released into the sea during the formation of submarine volcanoes and thick oceanic plateaus on ocean ridges. This ferrous iron (Fe2+) combined with oxygen to precipitate as ferric hematite (Fe2O3) and form banded iron formations on the sides of volcanoes.
  
• Some Archean rocks in the Greenstone-granite region (a volcanic rock-rich region of primitive oceanic crust and island arcs) formed at or near the Earth's surface and therefore preserve evidence of early atmospheres, oceans and life forms.
  
•  The greenstone-granite zone is dominated by marine lavas, island arcs and oceanic plateaus, and often includes rock types such as basalt, andesite, rhyolite, granite plutons, oceanic cherts and ultramafic komatiites.
  
• Volcanic activity during the Archean period led to high concentrations of this gas in the atmosphere. This high concentration of gas is thought to have caused a greenhouse effect in the atmosphere, warming the surface enough to prevent glaciation.
  

The granite-gneiss belt exposes the base of many Andean continental margins and contains rocks highly deformed and recrystallized by deep crustal metamorphism.