Sands of Time:First Cells and theTree of LifeCharley Kirlinkus4 billion yrs.3.5 billionOldest known sedimentary rocksBanded iron for mation, Isua,Greenland-- 3.7 billion year s oldCar bonaceous graphite par ticlesFr om banded iron of Gr eenland3.7 billion year s oldratio 12C to 13C in gr aphiteparticles s uggest they might be produced fr om living cellsPresence of free O2In iron-oxide-rich bandsBanded-Iron Formations(between 3.5 billion - 2 billion yrsJ. W. SchopfCr adle of Life ( 1999)Besides fossils, which are extremely spotty in the fossil record, what otherapproach can we use to infer the earliest living cells?18S rRNAWoese (1996)J. W. SchopfCr adle of Life ( 1999)Lateral Transfer of GenesHorizontal TransferJ. W. SchopfCr adle of Life ( 1999)Origin of organelles:mitochondria and chloroplastsProteobacteriaCyanoobacteriaUsing Gene Families to Root the TreeFirst Cells1. Chemical systems existed before they became packagedInto cells-- “primordial naked genes” able to self-reproduce.2. Their chemical makeup caused these living molecules tocluster together into globules, like ancestors of walled cells.3. First cells were powered by a simple form of metabolismthat laid the foundation for later complicated metabolism.J. W. SchopfCradle of Life (1999)J. W. SchopfCr adle of Lif e (1999)Probably lookedmuch like a bacteriumDid the common ancestoruse DNA to store information?Eucarya are vastlydifferentParsimonyEEARLY WORLD3.5 billion yrs ago -- Apex Chert, AustraliaApex Chert Fossils of Western Australia3.5 billion yrs. Living1.5 billionLivingLivingLiving850 Ma950 MaJ. W. SchopfCr adle of Life ( 1999)2.1 billionCyanobacteriaPhotosyntheticO2-producingUtilize CO2+H20Eukaryotic Algae2 billion yrsSingle-cell Eucarya fossilsEarliest ~ 2 billion yrs.1. What was Earth’s environment like when life arose?2. How is life defined, and how did it arise from non-life?3. What were the characteristics of the very first cells?HARD
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