Chapter 25 Monday February 8 2016 2 23 PM Chapter 25 The History of Life on Earth History of Life on Earth Macroevolution o 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 species o Arising by speciation o Subject to more microevolution o Followed by more followed by more speciation events or extinctions Adaptive radiation when many species with diverse adaptations descend from one ancestor species o Promoted 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 adaptations o Adaptive radiation has occurred small scale in isolated island groups o Throughout history major radiations followed mass extinctions Red represents extinction rates extinction radiation extinction radiation How did Major Changes in Form Arise Novelties May Evolve Gradually o By 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 across the 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 functional By 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 o Egg through mitotic process o Developmental genes control development of multicellular organisms o Regulatory 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 form o Mutations 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 paedomorphosis o Mutations 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 wings o Mutations 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 o Earth s Physical History Planet formed 4 6 billion years ago o Molten 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 water o Haydean 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 ago o Condensed water formed global ocean o Crust 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 land o Moving plates after volcanic forms merged islands into continents and created areas of shallow seas o Formed by volcanic activity o Before 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 drift o Single continent Pangaea by end of Paleozoic Era 250 million years ago signified end of Era o Breakup of Pangaea and further drift directly affected Climate Species distribution Speciation How Do We Know the History of Life The Fossil Record o Fossils are any remnant of dead organism that has changed in form remnants casts or traces o Fossils 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 Fossils o Relative dating compares strata rock layers Relating one layer to another Same fossil same age rock layer o Absolute 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 Scale o Hadean Eon 4 6 bya Origin of earth 4 6 bya World was on fire o Archaean Eon 3 8 bya o o First cells prokaryotic life 3 5 bya Oxygen revolution photosynthesis by prokaryotes changes air and water to O2rich 2 7 bya First rocks Proterozoic Eon 2 5 bya First eukaryotic cells 2 1 bya Internal organelles First multicellular life First animal life Phanerozoic 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 vertebrates amphibians First vertebrates with shelled eggs amniotes Completely independent of staying in water did not have to return to water for reproduction