THE FIRST CELLS Cellular Evolution Shape and appearance unknown – no fossils First cells were probably prokaryotic Modern prokaryotes called archaea are the closest relatives of Earth’s first cells

MAKING PROTEINS Life requires proteins - Next big step after formation of amino acids Amino acids could have formed proteins by binding to clay particles Clay backbone – helped keep amino acid groups from breaking apart

GENETIC CODE MOLECULES TO CELLS Most consider RNA to be life’s first coding system All DNA based life forms also have RNA RNA sequences appear to have changed very little through time MOLECULES TO CELLS Formation of membranes allowed early metabolic and replication pathways to develop Overall path from molecules to cells is still unknown

PHOTOSYNTHESIZING PROKARYOTES Archaea are autotrophic Are not photosynthetic Do not need oxygen Photosynthetic prokaryotes evolved later Cyanobacteria developed at least 3.5 BYA Signaled by spike in O2 levels Lead to development of Ozone (protection from harmful UV)