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Ast1141Lec15HistoryofLife.pptx - The History of Life on...

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The History of Life on EarthAstronomy 1141Mary Parrish
Uncovering Our HistoryWe can use radioactive age-dating to preciselyage different rocks in the geological column.We see different fossils in rocks of different agesThis allows us to reconstruct the history of livingthings on EarthFor living things (and, in rare cases, fossils) wecan also reconstruct their DNA and map therelationship between species
PhanerozoicHadean(3.8 – 4.5 Gyr ago):Formation of the Earth, oceans, and first atmospherePunctuated by sterilizing asteroid bombardmentsArchean(2.5 – 3.8 Gyr ago)Starts at end of the epoch of heavy bombardmentwhen Earth and its oceans stabilize.The oldest living things on Earth emerged sometimeduring theArchean Eon.
Major Challenges in the Study of Early Life onEarthVery few old rockssurviveThe earliestorganisms weresingle-celled; they willbe far less likely topreserve fossilevidence that theyexisted
Chalk&flintconsist primarily oftiny shells, the remains of marineanimals.chalk= calcium carbonateMicrofossils(a millimeter or less in size) are far morecommon than large fossils.flint= silicon dioxide
Shark Bay, Western AustraliaLake Thetis, Western AustraliaStromatolites today are foundin shallow bays & salt lakes.Stromatolitesare layered rocks made of sedimentstrapped by a mucus-like secretion from colonies ofcyanobacteria.
The tiniestmicrofossilsare the remains of individualcells: old microfossils are scarce.In well-preserved microfossils, we see outlines ofcellular structures and detect organic compounds.3.2 Gyr old microfossils:possiblyeukaryotic1.4 Gyr old microfossils:definitelyeukaryotic
Carbon has 2 stable isotopes:12C and13CAutotrophs take up12C more readily than13C, andso they aredepletedin13C relative to12C.

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Term
Fall
Professor
Tendrup
Tags
Bacteria, Snowball Earth, Proterozoic

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