Archean Eon

Archean eon

Formed 4.0-2.5 billion years ago

Beginning and end when

B = Acosta gneiss, E = plate tectonics become more modern

Earths atmosphere

3.7 billion years and the addition of O2

Shale and chert banded into what

BIFS (banded iron formations), important because that shows oxygen

Cratons

Protocontinents crashing into each other, and one day form the major continents

Platforms

Younger (protozoic) called “basement rocks” usually stable

Shields

Most ancient part of continents now, heavily faulted and intensely deformed (metaphoric), now very stable and highly resistant to change

Archean impact

3.26 an astroid hit → big tsunami evaporates oceans → but nutrients rise (phos. And iron) → spread globally → aids in marine life bloom

Pangolia glacification

Earths first ice age