EVOLUTION OVERVIEW In talking about the fossil past we need to understand that the world did not always look the way it does now In particular the continents used to be in different locations with different climates and vegetation The significance for us is that the environment was changing A changing environment means there was natural selection resulting in variation Vocabulary bya billion years ago mya million years ago ya years ago Scientific notation Genus is always capitalized Specific epithet is never capitalized Both are italicized when typed printed when handwritten they are underlined Genus may be abbreviated when understood Homo sapiens H sapiens Estimate age of universe about 15 billion years Formation of earth about 4 5 bya First life on earth 3 6 bya organic molecules By 2 4 bya oxygen in atmosphere Around 1 bya the beginning of sexual reproduction 530 mya first vertebrates 425 mya fish complex land plants land animals 235 mya dinosaurs 220 mya true mammals Theory of Plate Tectonics the Earth s outermost layer is fragmented into a dozen or more plates that move We call this movement continental drift http www ucmp berkeley edu geology tecmech html Feb 22 2005 The main features of plate tectonics are The Earth s surface is covered by a series of crustal plates The ocean floors are continually moving spreading from the center sinking at the edges and being regenerated Convection currents beneath the plates move the crustal plates in different directions The source of heat driving the convection currents is radioactivity deep in the Earth s mantle http www ucmp berkeley edu geology tecmech html Feb 22 2005 TYPES OF PLATE MOVEMENT Convergence Divergence and Lateral Slipping http www enchantedlearning com subjects astronomy planets earth Continents shtml 22 Feb 2005 New oceanic crust forms along a mid ocean ridge Subduction occurs where a heavier oceanic plate meets and goes under a continental plate http www ucmp berkeley edu geology tecmech html Feb 22 2005 Where two oceanic plates meet volcanoes may form Where two plates collide and move laterally sideways to each other earthquakes Where two continental plates meet mountains may form http www enchantedlearning com subjects astronomy planets earth Continents shtml 22 Feb 2005 The original large landmass was Pangaea which existed during the Permian through Jurassic periods 235 ca 200 mya http pubs usgs gov publications text historical html anchor4833509 21 Feb 2005 At the time of Pangaea 235 200 mya The earth was tropical The first primitive dinosaurs appear The very first mammals appear These earliest mammals were tiny and probably nocturnal So in thinking about spread of mammals the earliest mammals were present when there was just one large landmass By the end of the Triassic beginning of the Jurassic 200 mya Pangaea was splitting into two large landmasses Laurasia and Gondwanaland Laurasia North America Eurasia Gondwanaland South America Africa Australia Antarctica and India http pubs usgs gov publications text historical html anchor4833509 21 Feb 2005 At about 200 mya when Pangaea was splitting into Laurasia and Gondwanaland end of the Triassic beginning of the Jurassic period The Triassic period ended with a mass extinction accompanied by huge volcanic eruptions about 208 213 mya Most of the early primitive dinosaurs went extinct but other more adaptive dinosaurs evolved in the Jurassic Possible causes for this late Triassic extinction global cooling or an asteroid impact This extinction allowed the newer dinosaurs to expand into many niches that were now unoccupied Dinosaurs would become increasingly dominant abundant and diverse and remained that way for the next 150 million years Early mammals were roaming the forest floors and the first birds 150 mya had also appeared About 140 mya the first flowering plants appear beginning of Cretaceous period These are to become important food sources for mammals and early primates The Cretaceous period 146 65 mya was the heyday of dinosaurs Mammals and flowering plants were developing The Cretaceous ended 65 mya with massive world wide extinctions including the extinction of dinosaurs except for birds asteroid impact This marks the end of the Mesozoic Era The beginning of the Cenozoic Era and beginning of the Tertiary period one period of main interest to us in this class Our main periods of interest Asteroid extinctions end of dinosaurs Dinosaurs 1st flowering plants Splitting Laurasia Gondw Mass extinctions Pangaea is tropical dinosaurs 1st mammals Kottak 2004 146 SUMMARY prior to 65 mya Continents have moved climate has changed Theory of Plate Tectonics explains how continents have moved continental drift While Pangaea was the only landmass and when Laurasia and Gondwanaland pulling apart prior to 65 mya there were a lot of dinosaurs Mammals were small nocturnal Flowering plants developed food source for mammals Huge change at 65 mya asteroid hit earth All dinosaurs except birds went extinct End of Cretaceous beginning of Tertiary period end of Mesozoic beginning of Cenozoic Era 65 mya At that time North America was connected to Eurasia but not to South America Most landmasses were tropical or subtropical Now that dinosaurs are extinct there is a major mammal radiation Geologic Time Scale ERA Period Epoch 1 7 mya 5 mya 24 mya 36 mya 55 mya 65 mya http www ucmp berkeley edu cenozoic cenozoic html 22 Feb 2005 To summarize the Era of most interest to us Within the Cenozoic Era Tertiary Period 65 mya 1 7 mya Quaternary Period 1 7 mya now Within the Tertiary Period from oldest to most recent the geological epochs are Paleocene Eocene Oligocene Miocene Pliocene remember PEOMP Within the Quaternary Period from oldest to most recent the geological epochs are Pleistocene 1 8 mya 10 000 ya Holocene 10 000 ya now
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