Precambrian Overview:

Haden  4.6-4 bybp

        Earliest rocks form

        No True Continents

 

Archean 4-2.5 bybp

        Crust:  Granite and Gneiss represent continental material

                      Greenstone belts show oceanic matter

                      Hadean volcanic islands collide and form cratons and protocontinents

        Atmosphere:  Early atmosphere develops (~1% oxygen by end)

        Life:  Prokaryotic cells that are photosynthesizing

        Oceans: Early oceans form

 

Proterozoic 2.5 bybp to 560 mybp

        Crust: More felsic crust develops with passive continental margins

                      Larger continents form (Laurentia: proto-N. America)

                       Supercontinents develop:   Rodina 1.3 bybp to 750 mybp (Grenville Orogeny) 

                                                                   Pannotia 650 to 560 mybp

       

        Climate and Atmosphere: 2 episodes of glaciation

                                                    Atmosphere ~10% oxygen (banded iron formations and red beds)

       

        Life: Start with prokaryotic cells à  Eukaryotic cells ~2.1 bil years

                 Edicarian period (670-570 mybp) soft bodied micro-organisms w/evidence of early skeletons