Sands of Time 4 billion yrs 3 5 billion First Cells and the Tree of Life Charley Kirlinkus Oldest known sedimentary rocks Car bonaceous gr aphite par ticles Fr om banded ir on of Gr eenland 3 7 billion year s old Banded ir on f or mation Isua Gr eenland 3 7 billion year s old r atio 12C to 13C in gr aphite par ticles suggest they might be pr oduced f r om living cells Presence of free O2 In iron oxide rich bands Banded Iron Formations Besides fossils which are extremely spotty in the fossil record what other approach can we use to infer the earliest living cells between 3 5 billion 2 billion yrs J W Schopf Cr adle of Life 1999 18S rRNA Woese 1996 Lateral Transfer of Genes J W Schopf Cr adle of Life 1999 Horizontal Transfer J W Schopf Cr adle of Life 1999 Origin of organelles mitochondria and chloroplasts Proteobacteria Cyanoobacteria Using Gene Families to Root the Tree First Cells 1 Chemical systems existed before they became packaged Into cells primordial naked genes able to self reproduce 2 Their chemical makeup caused these living molecules to cluster together into globules like ancestors of walled cells 3 First cells were powered by a simple form of metabolism that laid the foundation for later complicated metabolism J W Schopf Cr adle of Lif e 1999 J W Schopf Cradle of Life 1999 Did the common ancestor use DNA to store information Parsimony Probably looked much like a bacterium E Eucarya are vastly different EARLY WORLD Apex Chert Fossils of Western Australia 3 5 billion yrs ago Apex Chert Australia 3 5 billion yrs Living Living 950 Ma Eukaryotic Algae Photosynthetic Cyanobacteria 850 Ma Utilize CO2 H20 Living 1 5 billion O2 producing Living 2 billion yrs 2 1 billion J W Schopf Cr adle of Life 1999 Single cell Eucarya fossils HARD QUESTIONS 1 What was Earth s environment like when life arose 2 How is life defined and how did it arise from non life Earliest 2 billion yrs 3 What were the characteristics of the very first cells
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