EESA05 - Environmental Hazards - Lec 11 : Mass Extinction (near-verbatim)

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Environmental Science
Mandy Meriano

EESA05 Lecture 11: Mass Extinction PY Date: Nov 27, 2012 Slide 3: Learning Objectives  Know the differences between asteroids, meteoroids and comet  Understand the physical processes associated with airbursts and meteorite impacts  Understand the physical processes associated with airbursts and meteorite impacts  Understand the possible causes of mass extinction  Know the evidence for the impact hypothesis that produced the mass extinction at the end of the Cretaceous period  Know the likely physical, chemical and biological consequences of impact from a large asteroid or comet  Understand the risk of impact or airburst of extra-terrestrial impacts and objects Slide 4: Mass Extinctions  Sudden loss of large numbers of plants and animals relative to # of new species being added o Extinction = not just an absolute destruction of all living organisms; it’s a relative net loss – losing more than gaining new species – mass extinction  Defines the boundaries of geologic periods or epochs o Clearly see mass extinctions that relates to what was happening during that time  Usually involve rapid climate change, triggered by: o Plate tectonics  Moves habitats to different locations o Volcanic activity  Large eruptions release CO2, warming Earth  Volcanic ash reflect radiation, cooling Earth o Extraterrestrial impact  Meteorite impact or asteroids (very large); anything from cosmic hitting Earth o Any changes in major cosmic rays that’s approaching or reaches the Earth’s surface  Mass extinctions = when any changes on planet happens so fast that the organisms can’t adjust – rate of change quick – organisms lost o Climate, sea level change; Slide 5: Mass Extinction  The history of life is the history of loss o Has happened always o We lose species but we find and there’s creation of new species o Balance between the 2  Most (99.9%) of all species that have ever lived have died out; new species have come up out of those extinctions  Many ‘mass extinctions’ in the past 600 million years Slide 6: The greatest extinction of all time…  Involved animals like these 1 EESA05 Lecture 11: Mass Extinction PY Date: Nov 27, 2012  Trilobites, crinoids, brachiopods, and innumerable other creatures vanished, leaving behind only their fossils (and in some cases, descendants)  Estimates of up to 90% of all species on Earth became extinct at the end of the Permian (250 million year ago) o Had shallow seas back then and organisms like such above o Fossils are one of the records that we have; these species existed we know Slide 7: The History of Life  Diversity has increased thru time  Graph: o Bottom: geological time – letters stand for protozoic, Cambrian etc; Silurian, carboniferous, Triassic, Jurassic etc; not testable – in millions of years o In Precambrian – had a drop –  # of families – phylums and species of organisms  The drops are some of the major extinction events that we had  Huge drop at the end of Permian – major extinction o KT event  Krotaceous Tertiary – also major mass extinction o Cm – cambrian; Pz - Paleozoic; Mesozoic, Cenozoic various eras – oldest to newest o Geologic time divided into eras/periods/diff time frames Slide 8: Life and Extinction  Fossils record the appearances of numerous forms of life, most of which have disappeared o Excellent record of what was here in the past  Disappearances, called extinctions, are a constant feature of life  Originations, in which new life forms appear, are approximately as frequent o Originations = speciation = the evolutionary process that we end up getting new organisms Slide 9: Mass Extinction  Every so often, the rate of extinction soars above the background level, and we recognize a major extinction event o The # of species really dropped compared to the background – major mass extinction  Graph: o Major drop in the # of species – based on fossil records o Dropped dramatically = mass extinction Slide 10: Six Major Mass Extinctions – geological time frames – vertical bar = shows various times Currently in Holocene MAJOR MASS EXTINCTIONS: 2 EESA05 Lecture 11: Mass Extinction PY Date: Nov 27, 2012  Ordovician o 446 mya o continental glaciation in Southern Hemisphere  Permian o 250mya o Volcanoes causing global warming and cooling o Pangaea formation – could have brought on loss of some of the species o Mass extinction doesn’t just mean that there would have been a meteor impact or rapid climate change; it can be a few diff factors working together to cause mass extinction – don’t have to happen in isolation  Triassic-Jurassic boundary o 202 mya o Volcanic activity associated with breakup of Pangaea o Lost all dinosaurs  Cretaceous-Tertiary boundary (K-T boundary) o 65 mya o Asteroid impact  Eocene epoch o 34 mya o Plate tectonics  Pleistocene epoch o Initiated by airburst o Continuous today o Caused by human activity Slide 11: Causes for Extinctions  Possible mechanisms for mass extinctions include: o Tectonic  Sea level changes  Climate shifts due to the Wilson cycle  Continental positions  When we get supercontinents – ex) Pangaea – you would have more uniform climate  The more diverse enviro, the greater diversity of organisms – if you reduce the diversity of just the climate, then you’ve reduced the # of organisms that have adapted to that climate  When you get supercontinent – during formation of supercontinent, climate becomes a lot more continental – if it’s hot, it’s really hot; if it’s cold, it’s really cold  Have less diverse climate pattern; climate = very continental  If you have land masses closer to poles – get lot of ice glaciers 3 EESA05 Lecture 11: Mass Extinction PY Date: Nov 27, 2012  Another change with supercontinent formation is that you don’t have as much activity anymore on ocean floor; closing of oceans  When continent are broken up, you have various rifts that are working – ridges with material coming out and pushing everything out  During supercontinent – we have lot more older sea floors – we get drop in sea levels  If continental mass is closer to poles – get more glaciers which means sea level lowered further  Most organisms live near shallow waters – once sea level drops – get a lot of loss in terms of # of organisms who used to live in shallower seas  Combination: climate, drop in sea level, volcanic eruptions etc; will result in mass extinctions o Volcanic  Dust  Atmospheric composition changes o Climate  Glaciation or torrid periods  Or increased variability o Extraterrestrial causes  Impacts  Cosmic ray bombardment  Earth has magnetic field = very great for us – because protects us from a lot of cosmic rays; if anything happens to this field, things can change  If magnetic field protection is weakened, then we get hit by a lot of cosmic rays that can result in major mass extinctions o Biologic causes  Species-area effect  Predation  Carnivores consume a lot of the organisms – go extinct  Disease  Bacteria/viruses that attack certain species – wipe them out  Flow chart – don’t have to memorize but know what happens with each change Slide 12: Causes for Extinctions – TECTONIC (1)  Changes in sea level will change the relative amount of low-lying land and shallow waters, which tend to be the places where the most living things are found  A drop in sea level could increase the amount of land from 29% to 40%  A rise in sea level could decrease land cover to 17%  When you have dispersed continents – lot of younger sea floor, a lot of magma coming out; if you have a major event with large volume of lava coming out – get real jump in sea level suddenly (from catastrophic submarine volcanic event); more variation in climate 4 EESA05 Lecture 11: Mass Extinction PY Date: Nov 27, 2012 Slide 13: Causes for Extinctions – TECTONIC (2)  Significant sea level changes have occurred in the past  One cause is related to the rate of seafloor spreading  Sea level rises when the volume of mid-ocean ridges increases  When sea level is high, parts of the continents are flooded by shallow seas, but when sea level falls, shallow seas disappear and extinctions occur  = loss of habitat/species Slide 14: Causes for Extinctions – TECTONIC (3)  Every 200-400 million years, the continents assemble into a supercontinent  The climate of a world with a supercontinent differs from the present one  Continental climates are extreme – hotter summers, colder winters, stronger monsoons, stronger storms – all tend to reduce the number of different environments present  As the continents move about on the surface of the Earth, they may pass over one of the poles  Typically, glaciation would result, which could also stress many species Slide 15: Causes for Extinctions – VOLCANIC  Episodic massive volcanic events occur – flood basalts – in which the total amount of volcanic activity increases dramatically (large volume of lava comes out); when flood basalts happen – major changes in climate = ash that gets into atmosphere (but not the main point), gases comes out (CO2 especially) – warming of our global climate o Large CO2 input into atmosphere – increase acidity of ocean water; when water and CO2 react – create weak carbonic acid H2C03 – increase in concentration of carbonic acid in ocean – more acidic – some organisms don’t like – if too quickly, can’t adjust to change  Ontong Java Plateau was formed over 120 million years ago by the outpouring of 36 million km3 of lava
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