Chapter-6-The-Origin-and-Evolution-of-Life-on-Earth -...

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Chapter 6 – The Origin and Evolution of Life on Earth6.1 – Searching for Life’s OriginGeological records are incomplete therefore we have not yet discovered theoldest intact fossils3 lines of fossil evidence point to idea that life arose quite early:oi)Stromatolitesrocks characterized by distinctive layered structureancient stromatolites look similar to mats formed today by“living stromatolites”living ones contain layers of sediment mixed w/ diff microbesthose on top gain energy through photosynthesisbeneath use org. compoundslayered structure caused by migration upwardsome controversy about biological origin b/c sedimentationcan mimic layeringscientists have confidence of existence as far back as 3.5 billionyears agoif we are correct about photosynthetic life existing 3.5 billionyears ago, can infer primitive life existed earlieroii)Microfossilsfinding microfossils tough b/c rocks become rare and alteredw/ agegreatest controversy over oldest microfossil of 3.5 billion yearsfound that rock formed near deep-sea vent therefore cannot bephotosynthetic b/c sunlight does not penetrate to deep seamicrofossils in rocks dated 2.7 – 3.0 billion years show moreconclusive evidence for life: contain mols which indicatebiological originin summary, evidence shows existence of life before 3.0 billionyears and life may have existed prior to 3.5 billion yearsoiii)Isotopic Evidenceliving organisms can change the ratios of isotopes from theirbackground, nonliving valuesGreenland, lower carbon-13 ratio found in rocks more than3.85 billion years old – suggests remnants of life from that timeThe rocks are metamorphic meaning no intact microfossilremains b/c of high pressure/heatMust assume rocks were once sedimenatary to contain lifeNew evidence:i) if Greenland rocks hold evidence of life we wouldexpect to find the same in other rocks of same date(rocks have been found)
ii) life can alter isotopic ratios – studies found presenceof characteristic ratios for lifeif we are right, it is likely life arose earlier than 3.85 billion years agoWhat did early life look like?When did life begin?
Where did life begin?

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