Môn Sinh học - Chapter 25: The history of life on earth

Ch. 25/26 Warm-UpList 3 pieces of evidence to support the endosymbiont theory.The half-life of carbon-14 is about 5600 years. A fossil with ¼ the normal proportion of C14 is probably _______ years old.Answer the following using the diagram below:a common ancestor for D & Fmost closely related speciesleast related speciesnew species C arises at this pointcommon ancestor for E & FBCDEF34215AChapter 25The History of Life on EarthWhat you need to know:A scientific hypothesis about the origin of life on Earth.The age of the Earth and when prokaryotic and eukaryotic life emerged.Characteristics of the early planet and its atmosphere.How Miller & Urey tested the Oparin-Haldane hypothesis and what they learned.Methods used to date fossils and rocks and how fossil evidence contributes to our understanding of changes in life on Earth.Evidence for endosymbiosis.How continental drift can explain the current distribution of species.How extinction events open habitats that may result in adaptive radiation.Early conditions on EarthDiscovery Video: Early LifeEarth = 4.6 billion years oldFirst life forms appeared ~3.8 billion years agoHow did life arise?Small organic molecules were synthesizedSmall molecules  macromolecules (proteins, nucleic acids)Packaged into protocells (membrane-containing droplets)Self-replicating molecules allow for inheritance“RNA World”: 1st genetic material most likely RNAFirst catalysts = ribozymes (RNA)Synthesis of Organic Compounds on Early EarthOparin & Haldane:Early atmosphere = H2O vapor, N2, CO2, H2, H2S methane, ammoniaEnergy = lightning & UV radiationConditions favored synthesis of organic compounds - a “primitive soup”Miller & Urey:Tested Oparin-Haldane hypothesisSimulated conditions in labProduced amino acidsProtocells & Self-Replicating RNAFossil Record: used to reconstruct historySedimentary rock (layers called strata)Mineralized (hard body structures)Organic – rare in fossils but found in amber, frozen, tar pitsIncomplete record – many organisms not preserved, fossils destroyed, or not yet foundBoth used to date fossils and determine age Relative DatingRadiometric DatingUses order of rock strata to determine relative age of fossilsMeasure decay of radioactive isotopes present in layers where fossils are foundHalf-life: # of years for 50% of original sample to decayGeologic Time ScaleEon  Era  Period  Epoch (longest to shortest)Present Day: Phanerozoic Eon, Cenozoic Era, Quaternary Period, Holocene EpochClock Analogy of Earth’s HistoryKey Events in Life’s HistoryO2 accumulates in atmosphere(2.7 bya)Humans(200,000)Endosymbiont TheoryMitochondria & plastids (chloroplasts) formed from small prokaryotes living in larger cellsEvidence:Replication by binary fissionSingle, circular DNA (no histones)Ribosomes to make proteinsEnzymes similar to living prokaryotesTwo membranesPangaea = SupercontinentFormed 250 myaContinental drift explains many biogeographic puzzlesMovement of continental plates change geography and climate of Earth  Extinctions and speciationMass extinctions  Diversity of lifeMajor periods in Earth’s history end with mass extinctions and new ones begin with adaptive radiationsMajor events during each EraPrecambrian: microscopic fossils (stromatolites)Photosynthesis, atmospheric O2Eukaryotes (endosymbiont theory)Paleozoic: Cambrian ExplosionPlants invade land, many animals appearPermian Extinction (-96% species)Mesozoic: “Age of Reptiles”, dinosaur, plantsFormation of Pangaea supercontinentCretaceous Extinction – asteroid off Mexico’s coastCenozoic: PrimatesNote: All end with major extinction & start with adaptive radiationDiscovery Video: Mass ExtinctionsEvolution of new forms results from changes in DNA or regulation of developmental genesEvo-Devo: evolutionary + developmental biologyHeterochrony: evolutionary change in rate of developmental eventsPaedomorphosis: adult retains juvenile structures in ancestral speciesHomeotic genes: master regulatory genes determine location and organization of body partsEg. Hox genesHox gene expression and limb development.Evolution of Hox genes changes the insect body plan.Exaptations: structures that evolve but become co-opted for another functionEg. bird feathers = thermoregulation  flight