National Museum of Natural Science

The Archean Eon began with the appearance of the oldest rocks on the earth. The oldest known rocks on the earth are the gneiss in the Acasta region of northwestern Canada, which formed 4 billion years ago based on SHRIMP U-Pb dating analysis (Bowring and Williams, 1999, Contrib Mineral Petrol). As water started to form on the primitive crust of the earth, the early hydrosphere may have been taking shape around 4 billion years ago. At the same time, there was the earliest sedimentation, gradually forming the crust’s sedimentary sphere, exposing the primitive continental crust that may have already existed in the hot magma ocean and molten surface within 600 million years of the earth’s birth.

Gneiss