Chapter 25Monday, February 8, 20162:23 PM Chapter 25: The History of Life on Earth History of Life on Earth-Macroevolutiono= major changes in life above the species level in earth's history How Did New Groups of Life Begin? (25.4)-Each lineage (group) began with one speciesoArising by speciationoSubject to more microevolutionoFollowed by more followed by more speciation events or extinctions-Adaptive radiation = when many species with diverse adaptations descend from one ancestor speciesoPromoted by new:-Habitats-Ecological roles (dinosaurs and then comes the extinctions of the dinosaurs due to a meteor strike, these large vertebrates wiped out, the mammals take on ecological role on being top predator or big herbivore-Key adaptationsoAdaptive radiation has occurred small-scale in isolated island groupsoThroughout history, major radiations followed mass extinctions-Red represents extinction rates, extinction = radiation, extinction radiation How did Major Changes in Form Arise?-"Novelties" May Evolve GraduallyoBy incremental adaptation (comes along and displaces it, major adaptations/changes have occurred in the past, only been slight improvements over older versions)-Each change is a better adaptation (same use)Improved version displaces the old-Ex. Mp3 player to iPods to phones…Walkman, cassette tapes (displaced by newer technology)-Ex. Complex squid eyes (the result of incremental changes, becomes an improvement)Limpets - crawls on its foot and glazes, sense a dark shadow going acrossthe body and shrink in (detect light and dark adapts to its need)Slit-shell snail - can tell light and dark activated from either side of the cup (means for telling directionality, where the threat is coming from)Other mollusk eyes have simpler but useful intermediate forms-Nautilus - pinhole camera (visualization)-Marine snail Murex - focusing lens-Squid - nerves to focus lens-Each one is a better adaptation, but each one is functionaloBy exaptation-= existing adaptation gets gradually modified for a different useEx. Function of fur/hair (insulation) ---> porcupine quills (defense) a modification of the hair (fusion of long hair that was normally for insulation) stiffer hair provides deterrent for predatorEx. Feathers first for insulation, later for flight; modifications for flight rather than just for insulation-Contour feathers could provide lift for hopping/gliding but muscles not strong enough to flyEx. Jaw hinge bones in reptile-like ancestors become ear bones in modern mammals-Present day mammals - stapes and extra two structures-Evolution and Development ("Evo-Devo")oEgg through mitotic process…oDevelopmental genes control development of multicellular organismsoRegulatory genes control when, where, and which genes are expressed-A single mutation may affect expression of many genes during developmentEx. A mutation in the DNA coding for transcription factors affects transcription for many proteins-Resulting in dramatic changes in final body formoMutations of genes controlling heterochrony of development leads to…-Change in growth rate of parts can produce a new final shape (difference in timing)-Paedomorphosis is a change of timing that produces a sexually mature adult with juvenile featuresA new species arisen by process of paedomorphosisoMutations of homeotic genes affect placement of body parts-Ex. Antennae supposed to appear on thorax, mutated antenna that looks like leg-Ex. Fly with recessive mutations for both genes, extra wingsoMutations of Hox genes (a type of homeotic gene) may explain body plan changes in animals-Ex. Hox gene suppresses limb formation in a snake-Mutation in an insect ancestor may have reduced the number of legs Earth's Physical History-Planet formed 4.6 billion years agooMolten rock surface; no liquid water-Earth's surface covered with molten rock - heavy material formed dense solid iron core and liquid outer core, lighter material outside; no liquid wateroHaydean - Greek Haydes, absence of water-Greek Haydes "Hell" hellacious place to live, absence of water - too hot for any life of any kind-Crust cooled, solidified 3.8 billion years agooCondensed water formed global oceanoCrust breaks into moving "plates"-(recognize what is going on with plate tectonics)-Mantle continues to heat up because of radioactivity in the core and hot rock goes to the surface, cools down, dropping back down into the mantle - plate tectonics,begin to move around-Volcanoes created first landoMoving plates (after volcanic forms) merged islands into continents and created areas of shallow seaso(Formed by volcanic activity)oBefore ~2.5 billion years ago, early air was low in O2 and high in volcanic gases-(in that atmosphere where first life appeared)-Then photosynthesis changed air to O2-rich-That is now acceptable in our kind of life-Moving plates caused continental driftoSingle continent Pangaea by end of Paleozoic Era (250 million years ago) - signified end of EraoBreakup of Pangaea and further drift directly affected:-Climate-Species distribution-Speciation How Do We Know the History of Life?-The Fossil RecordoFossils are any remnant of dead organism that has changed in form (remnants, casts or traces)oFossils tell us-Anatomy: muscle scarring on bones, etc.-Habitats: fish fossils on rocks show evidence of past water or broad leaf plants-Diet and lifestyle: slashing vs. grinding teeth or trails on floor/ocean-Genetic info (DNA)-Dates From Rocks and FossilsoRelative dating = compares strata (rock layers)-Relating one layer to another-Same fossil = same age rock layeroAbsolute dating = age in years before present-Radiometric dating uses decay rate of radioactive isotopesChanges from carbon to nitrogen (beta-particles)-Half-life = time needed for 1/2 the amount of isotope to decay[25.6] History of Life-Geologic Time ScaleoHadean Eon (4.6 bya)-Origin of earth (4.6 bya)World was "on fire"oArchaean Eon (3.8 bya)-First cells (prokaryotic life) (3.5 bya)-Oxygen revolution - photosynthesis by prokaryotes changes air and water to O2-rich (2.7 bya)First rocksoProterozoic Eon (2.5 bya)-First eukaryotic cells (2.1 bya)Internal organelles-First multicellular life-First animal lifeoPhanerozoic Eon (535 mya)-Paleozoic Era (535 mya)Cambrian explosion of animal diversity-Before there was only a phyla of animals, after there was a diversity of animals along with phylaAge of fishesInvasion of land by plants, fungi and arthropodsFirst land