Class 9 : Geological ages, life on Earth, and mass extinctions

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Class 9 Geological ages, life on Earth, and
mass extinctions

• Geological ages and some important geological
  terminology
• Development of life on Earth
• Introduce idea of mass extinctions

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I Life on Earth

• Before 3.8 billion years ago, heavy bombardment
  vaporized surface of oceans
• Any emergent life would be killed
• First life appeared 3.5-3.8 billion years ago.
• Simple, single-celled organisms (like modern
  bacteria)
• First multi-cellular life 1 billion years ago.
• From then on, things went quite quickly

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• Life moved onto the land 570 million years ago
  start of Cambrian period
• Microbes first, then plants, then animals
• Spread rapidly across the lands, adapting to
  different environments
• Dinosaurs were walking the Earth by about 225
  million years ago

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II Dinosaurs
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• Most successful species to inhabit Earth
• Amongst biggest animals to ever live
• Adapted to most environments
• Top of food chain
• Then, 65 Myrs ago, they all died!

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III The geological time-machine

• The geological record
• Diving deeper into the Earths surface
  corresponds to going back in time
• Old rocks/fossils are deeper.
• 65 million years ago, an event occurred
• Ended the Cretaceous Period (and Mesozoic Era)
• Started the Tertiary Period (and the Cenozoic Era
  the current era)
• Called the K-T transition
• A lot of evidence suggests that a 10km asteroid
  hit the Earth at this point in time

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IV The K-T extinctions

• At the K-T boundary, 70 of all species became
  extinct.
• Was extinction sudden or gradual?
• Many geologists believe that dinosaurs were
  already starting to become extinct even before
  any possible asteroid impact
• If so, impact may have helped extinction but was
  not the primary cause.
• But its very difficult to say whether extinction
  was gradual or sudden

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• Ideally, if extinction were sharp, there would be
  a depth above which fossils suddenly disappeared.
• But several things can disrupt/blur the ideal
  time-ordering of strata
• Bioturbation (sedimentary rock disturbed by
  tunneling animals)
• Reworking (sedimentary rock disturbed by
  non-biological factots waves etc.)
• Erosion (can produce missing strata)
• Debate rages on but the hypothesis of sudden
  extinction at KT boundary has yet to be refuted.