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History of Life

A. Radioscopes are used to estimate the ages of fossils and rock layers
    1. HC can be used to date fossils about 30,000 years old or younger (half-life is ca 5700 years).
    2. 40K has been used to date many older events in Earth history (half-life is ca. 1.3 billion years; decays to 40Ar).
B. Geologists have divided the history of Earth into eons, eras, periods, etc. based on fossils found in different layers (strata) of rock.
    1. age of divisions vs. their duration
C. Earliest prokaryote fossils = ca. 3.5 billion years old (3.8 billion years ago - estimated time of origin)

D. Earliest bacteria that evolved the ability to use H20 as a source of H for their metabolism liberated O2
    1. As O2 levels increased, organisms evolved the ability to use O2, metabolically.
E. O2 levels in atmosphere have been gradually increasing during Earth history.
    1. only tiny cells would be able to survive in the low oxygen environment of early Earth (surface area/volume ratio)
    2. greater amounts of O2 allowed evolution of larger cells
    3. eventually enough O2 was available to support multicellular life
F. Major processes of change on Earth
    1. continental drift
      a. sea floor spreading - new crust is added from the mantle at rifts in the sea floor
      b. this causes continents to move
      c. when plates meet, they slide past each other or one goes under the other (can result in formation of mountains)
      d. affects climate, sea level, ocean currents, distribution of organisms, volcanic activity
      e. Pangaea - all continents together, harsh climates in interior (properties of water)
      f. Laurasia - North America, Europe, Asia
      g. Gondwanaland - South America, Africa, Madagascar, India, Australia, Antarctica
    2. shifts in climate
      a. Earth's orbit sometimes changed slightly
      b. change in ocean currents
    3. volcanic activity
      a. major volcanic episodes can affect Earth's climate
      b. ash in the atmosphere reduces penetration of sunlight, reducing temperatures
    4. meteroites
      a. small meteorites regularly hit Earth
      b. large meteor collisions are rare but do occur (Kansas, 1948, 5 ton meteor)
      c. mass extinction at end of Cretaceaous (about 65 mya) have been caused by a meteor collision
        - estimated size - 10 km diameter
        - a large crater (180 km diameter) was found of coast of Yucatan
        - thin layer of iridium
        - this hypothesis is still debated but has fairly strong support
G. Major events in history of life (times are estimates)
    1. Earth forms - 4.6 bya
    2. origin of life - 3.8 bya (prokaryotes)
    3. oldest known fossils - 3.5 bya (stromatolites - left by bacteria)
    4. O2 begins accumulating - 2.5 bya
    5. oldest eukaryote fossils - 1.5 bya
    6. first animals - 700 mya
    7. origin of most invertebrate phyla; diverse algae - Cambrian (544-500 mya)
    8. first vertebrates (jawless fishes); abundant marine algae - Ordovician - probably due to extensive glaciation
H. Three major faunas
    1. Cambrian explosion (ca. 500 mya)
      a. gave rise to most animal phyla
      b. Burgess Shale in British Columbia
      c. Wonderful Life by S.J. Gould
    2. Paleozoic fauna (ca. 440 mya)
      a. first animals colonize land
      b. many new families, genera, etc. but no new phyla (i.e., no significantly different body plans)
    3. Modern fauna (ca. 200 mya)
I. In general size and complexity of species increases within lineages.
    a. notable exception - insects
J. Interactions of predators and prey shape evolutionary history.
    a. arms race
    b. shells and shell breakers
    c. toxins and tolerance
K. Major U.S. Natural History Museums
    1. Smithsonian - Washington D.C.
    2. American Museum of Natural History - New York
    3. Carnegie Museum of Natural History - Pittsburgh
    4. California Academy of Natural History - San Fransisco
    5. Field Museum of Natural History - Chicago
    6. Dallas Museum of Natural History (not as big but closer)
L. Humans now more than ever, are affecting the fate of other organisms
    1. Humans alter environments
      a. pollution
      b. habitat destruction
      c. oil spills
      d. pesticides/herbicides
      e. fertilizer
    2. Humans effect geographic distribution of species.
      a. zebra mussel
      b. lamprey
      c. rats, cats, etc.
      d. brown tree snake
    3. Humans cause extinction
      a. directly by over harvesting
        - great auk
        - passenger pigeon
      b. indirectly by altering environment
        - ivory-billed woodpecker
      c. current rates of extinction are estimated to be on the order of a mass extinction
    4. artificial selection

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