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History of Earth: Geologic Time Line


... and CO2, so earth did not freeze over Oceans formed as rain fell Bacteria, protozoa, algae, corals, worms, jellyfish, sponges and fungi exist. – PowerPoint PPT presentation

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Title: History of Earth: Geologic Time Line

History of Earth Geologic Time Line
(No Transcript)
Geologic time scale-another view
Hadean Era (Earth formed 4.63 BYA)
  • Earth is molten
  • Compounds, but no life exists

Archaean Era (Begins 3.73 BYA)
  • First Cell forms
  • Photosynthesis begins
  • Endosymbiotic theory

EndOsymbiotic theory
Archaean era
  • Meteor bombardment ends
  • Sun 30 dimmer, but atmosphere consisted of
    nitrogen, water vapor, methane, and CO2, so earth
    did not freeze over
  • Oceans formed as rain fell

Proterozoic era (from 1 bya)
  • Bacteria, protozoa, algae, corals, worms,
    jellyfish, sponges and fungi exist.
  • Photosynthesis on land begins
  • Most life was unicellular because there was no
    protective ozone layer to filter UV rays.
  • Most life was aquatic because water filtered the
    UV rays.
  • First snowball earth ice agepossible because
    continents were all close to equator at that

Snowball Earthwhat saved us??
  • The carbon cycle has always moderated our

How did life survive?
  • Single-celled organisms survived in water
    channels within ice and deep sea vents

Paleozoic era--age of land plants
Paleozoic era
  • Begins with the Cambrian explosionexplosion of
    new life formsevery phylum is represented within
    50 million years
  • Multicellular life requires a stable environment
    and oxygen to survive. Scientists arent sure
    what caused rise in oxygen.
  • Hard shells and bones developed, so the fossil
    record is abundant.
  • Land plants emergedcooled planet by accelerating
    carbon cycle

Late paleozoic era
  • Largest mass extinction to date85 of life
    became extinct
  • Scientists arent sure of causedeep seas became
    anoxic and climate warmed (global warming?)
  • Could have been caused by massive volcanic

Mesozoic era-The age of dinosaurs
FYINewest chemical analyses suggest that
dinosaurs had brightly colored patterns on their
skin and many of them had feathers around their
feet and legs.
Mesozoic era
  • Age of reptiles
  • Amphibians and small mammals also flourished
  • Mass extinction at end of Mesozoic eraprobably
    caused by large meteor impact close to Yucatan
  • Dinosaurs died out

Cenozoic erathe age of mammals
Cenozoic era
  • Age of mammalsmammals radiated widely after
    competition from dinosaurs was diminished
  • Endothermicallowed them to live in a variety of
  • Angiosperms also spreadprotected seeds made them
    fit for environment
  • Continents drifted apart, currents trapped around
    Antarctica made it get colder and freeze, which
    cooled atmosphere, causing another ice age

Cenozoic EraHumans emerge
  • Last mass extinctions (mammoth, saber toothed
    tigers) caused by overhunting by humans
  • Humans then began to domesticate crops and

Fossilsour peak into the past
  • Fossil formation
  • Requires the organism to be buried fairly quickly
    before it is decomposed entirely
  • This type of fossilization only preserves hard
    tissue (bones), so scientists must hypothesize
    what soft tissue is like

Dating Fossilsrelative dating
  • One way to date fossils is by relative dating.
  • Fossils found toward the surface are assumed to
    be younger than deeper fossils
  • Since some rock layers will have washed away,
    exposing older layers, scientists will confirm
    dating by using an index fossila fossil whose
    age is known to date the layers fossils are found

Dating fossilsradioactive dating
  • Some elements are radioactive and will decay
    (become un-radioactive) at a predictable pace
  • One of these elements is carbon-14, which is in
    the tissues of every living organism.
  • When an organism dies, the carbon-14 in its body
    begins to decay
  • Scientists can look at how much carbon-14 is left
    in a fossil to determine its age
  • Scientists are also now looking at rubidium
    content (another radioactive isotope) because it
    allows accurate dating of older specimens
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