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Macroevolution - Halton District School Board ... Macroevolution – PowerPoint PPT presentation

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Title: Macroevolution

The Beginning
  • Scientists have tried to figure out the initial
    conditions and events that may have resulted in
    the origin of life, however, this research is
    ongoing as scientists test hypotheses about
    origins and evolution.
  • We believe that Earth was formed about 4.6
    billion years ago
  • It was extremely hot. Heat generated by asteroid
    impacts, internal compression and radioactivity
    melted most of the rocky material on Earth.
    Heavy materials formed Earths inner core and
    less dense materials formed a thick mantle, while
    the least dense rock floated on the surface and
    cooled to form a crust.

  • Hot gases formed Earths primitive atmosphere,
    then when the amount of asteroids hitting Earth
    slowed down, the surface temperatures were able
    to cool down.
  • Early Earth would have contained large amounts of
    nitrogen gas, CO2, carbon monoxide and water
  • Because oxygen gas is highly reactive, and the
    temperatures were very high, there would be very
    little, if any oxygen gas in the atmosphere.
  • There were some amounts of other vapours on
    primordial Earth such as hydrogen sulfide,
    ammonia, and methane.

  • There were a lot of intense sources of energy
    radioactivity, intense UV, visible light, cosmic
    radiation, heat from volcanic activity, and
    electrical from violent lightning storms.
  • Primary abiogenesis is a theory that the first
    living things on Earth arose from nonliving
  • Urey and Miller were two scientists who tested
    the theory by putting a few inorganic materials
    together that would be found on primordial Earth,
    and exposed them to electrical sparks, which
    actually modeled the early conditions of Earth.
    Their results were that after only one week, 15
    of the original carbon had formed into aldehydes,
    carboxylic acids, urea and two amino acids.

  • Chemical evolution is believed to have taken
    place and organic materials came together with
    the amount of heat that was available it gave
    rise to more complex polymers and organic
  • These molecules went through self-replication and
    catalytic activity.

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  • Scientists believe that life has existed on Earth
    for more than 3.5 billion years.
  • The first prokaryotic organisms would have relied
    on abiotic sources or organic compounds
  • The first photoautotrophs would come next, and
    they used water to breathe by taking off the
    Hydrogen and releasing the oxygen into the
  • This accumulation of oxygen would have been toxic
    to many anaerobic organisms, so while the
    photoautotrophs prospered, cells adapted to this
    change, others died.

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The Tree of Life
  • Macroevolution is large scale evolutionary change
    significant enough to classify groups or lineages
    into distinct genera or even higher level taxa.
  • This macroevolution has been punctuated by times
    of mass extinction as well as times of very rapid
  • A lineage is the descendants of a common ancestor

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  • Endosymbiosis (relationship in which a
    single-celled organism lives within the cell of
    another organism) is another important theory
    that scientists proposed that suggests that may
    have given rise to chloroplasts and mitochondria.
  • for the first 3 billion years of life on Earth,
    all organisms were unicellular.
  • Eubacteria gave rise to aerobic and
    photosynthetic lineages.

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Diversification and Mass Extinction
  • Earths History is divided into 5 eras based on
    dramatic changes in the fossil record.
  • There was a 40 million year period beginning
    about 640 million years ago where there was a
    huge increase in animal diversity called the
    Cambrian explosion
  • Major changes in the Earth have been caused by
    numerous events.
  • Formation of super continent Pangea would have
    caused coastal and terrestrial environments as
    well as changes in the global climate.
  • Huge asteroids hitting Earth (Impact hypothesis)
    causing tidal waves, debris, high concentrations
    of different materials.

  • Mass extinction periods are only 4 of all
    extinctions, however, and we must remember that
    extinctions usually happen due to the ongoing
    evolutionary changes.
  • Mass extinction periods are usually followed by
    periods of huge diversification.

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Cladistics and Phylogeny
  • Cladograms are used to illustrate evolutionary
    relationships of different groups of species.
  • Based on evidence from fossils, morphology,
  • Use the presence or absence of recently evolved
    traits called derived traits.
  • Two organisms that share a recently evolved trait
    is called a synapomorphy.

  • Page 351, try the sample problem and the practice

  • The theory of gradualism states that as new
    species evolve, they appear very similar to the
    original species and only gradually become more

Punctuated Equilibrium
  • The theory of punctuated equilibrium suggests
    that the process of evolution is slow, but
    occasionally punctuated by periods of rapid

  • Now it is widely accepted that both gradualism
    and punctuated equilibrium play a significant
    role in evolution.
  • When there is a quick change in the environment
    rapid evolution
  • environment changes slowly gradual