A Quick Look at the History of Life on Earth Part 2

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A Quick Look at the History of Life on Earth Part
2

• The Phanerozoic Eon
• Including the Paleozoic, Mesozoic and Cenozoic
  Eras

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Paleozoic Era

• Paleozoic old life
• - bounded by two major events in life history
• - begins with the Cambrian explosion
  543mya
• -ends with the Permian
• extinction over 90 of life
• disappeared 250mya

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The Cambrian Explosion

• a seemingly sudden appearance of large numbers of
  multicellular organisms in the fossil record.
• - Rocks older than this appeared to have no
  fossils (because they are too small to see, and
  because the multicellular organisms didnt have
  hard parts to preserve.
• Most types of multicellular organisms present
  today appeared at this time.
• Many other groups of organisms appeared and then
  went extinct during
• this period
• Successful forms tended to be large with shells
  or exoskeletons for support

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Other Paleozoic Highlights

• Early Paleozoic dominated by marine invertebrates
• Appearance and evolution of fish during the
  middle period of the Paleozoic first fish had
  no jaws and cartilage skeletons
• - Jaws developed
• - cartilage skeletons give way to bones.

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Paleozoic Highlights continued

• Major change in vertebrates tetrapods (animals
  with 4 limbs) appear in the mid-Paleozoic.
• - First as paired fins on fish, then later as
  legs.
• Amphibians and reptiles appeared.
• - Reptiles were not common until the
  next era, the Mesozoic.

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Paleozoic Highlights the move to land

• Life moved from the sea to land during the middle
  of the Paleozoic Era.
• - First bacteria and fungi make soil
• - followed by plants
• - then arthropods (insects, etc.)
• - finally vertebrates.
• Large areas of swamp vegetation from this period
  were converted into coal after being buried and
  compressed.

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Paleozoic Highlights- the move to land

• Why now?
• - The oceans had been the only shield life had
  against UV light
• - UV light damages DNA and
• threatens life
• - by the mid Paleozoic, oxygen in the upper
  atmosphere formed ozone (O3)
• - ozone blocks out much of the suns UV
  light making life on land possible

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Permian Extinction-the Dramatic End of
the Paleozoic Era

• Largest mass extinction in earth
• history - 250mya
• 90 of species disappeared
• Multiple ideas exist about the cause
• - massive volcanic eruptions in Siberia
  lasting 1 million yrs coincided with the
  extinction
• - climate change
• - evidence for both global warming and
  glaciation exists
• The mass extinction cleared the way for the rise
  of the dinosaurs
• during the Mesozoic era

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Mesozoic Era 250mya 65mya

• Mesozoic middle life
• Age of the dinosaurs
• - reptiles were the largest animals on land
  and in the sea during this period.
• major diversification of flowering plants late in
  the Mesozoic.
• Supercontinent Pangea breaks into many continents
  allowed speciation to occur in many different
  habitats.
• Birds and mammals appear but arent prominent.
• Ends with a mass extinction Cretaceous
  extinction

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Cretaceous Extinction

• Thought to have resulted from a large asteroid
  striking the earth
• - drove huge amounts of dust to into the
  atmosphere and blocked out sunlight reducing
  photosynthesis
• - reduced primary productivity
• - Evidence to support
• - worldwide layer of iridium found at
  correct age in rocks
• very rare in earth rocks common in
• meteors, asteroids, comets etc.
• - massive impact crater found off of
• the Yucatan penninsula of Mexico
• - 100 mi in diameter
• - correct age

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Cenozoic Era- 65mya - present

• Cenozoic New Life
• Mammals become the dominant life form on land.
  An adaptive radiation that took advantage of the
  sudden loss of dinosaurs.
• Another large group evolves the grasses.
• Adaptive radiation of birds and flowering plants.
• Fish, amphibians and reptiles dont change much
  during the Cenozoic.
• Geologically, continents that had been separated
  started to collide Africa with Europe, North
  America with South America, India with Asia
• Hominids appear 5 mya
• modern humans (genus Homo)2 mya
• - Homo Sapiens approx 200,000 ya

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Cenozoic Life
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Summary

• Earth forms 4.6 billion years ago
• Solid surface forms 4 billion years ago
• Life starts (?) 3.8 billion years ago
• Age of Bacteria Archaean era
• Oxygen atmosphere develops 2 billion years ago.
• Eukaryotes develop. Proterozoic era
• Edicarian life 650 million years ago. First
  multicellular life, forms unknown today
• Cambrian explosion most current life forms
  appear 550 million years ago
• Paleozoic era 550 250 million years ago.
  Marine invertebrates, fishes, amphibians,
  invasion of the land. Coal formation.
• Permian mass extinction 250 million years ago.
  95 of all life dies end of Paleozoic
• Mesozoic 250-65 million years ago. Age of the
  dinosaurs (reptiles). Mammals, birds, and
  flowering plants appear
• Cretaceous mass extinction asteroid hits the
  Earth, killing much of life, including the
  dinosaurs.
• Cenozoic era 65 million years ago till present.
  Mammals dominant