The History of Life

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Chapter 19

• The History of Life

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The Fossil record

• Palentologists study fossils
• These records provided evidence about the history
  of life on earth
• It shows that different organisms have changed
  over time
• Some even became extinct

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Interpreting Fossil Evidence

• Relative dating- used to determine the age of a
  fossil
• You compare the fossils placement in the rock
  layer with other fossils in the rock
• The rock layers are formed by age with the oldest
  on the bottom

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Index fossil

• Can be used if the species is easily recognized
  and existed for a short period but have a wide
  geographic range

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Radioactive dating

• Scientists calculate the age of a sample based
  ion the amount of remaining radioactive isotopes
  it contains
• The half life is the minimum amount of time it
  takes for half of a radioactive element to decay

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Geological time scale

• Used to divide time
• After precambrian time, the basic divisions of
  the geological time scale are eras, periods, and
  epochs

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eras

• Paleozoic era- 544 million years ago, vert and
  invert
• Mesozoic- 251 million yrs ago, dino and mammals
• Cenozoic- 65 million yr ago, mammal age

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Periods and epochs

• Period range in length from 10 million years to
  less than 2 million years
• Further divide periods into epochs

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Earths Early History

• Formation of the earth occurred 8.2 billion years
  ago
• Its early atmosphere contained hydrogen cyanide,
  carbon dioxide, carbon monoxide, nitrogen,
  hydrogen sulfide, and water

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First organic molecules

• Miller and Urey did an experiment which suggested
  how mixture of compounds could have arisen from
  simplier compounds present on primitive earth

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How Did Life begin?

• 1. formation of microspheres
• 2. evolution of RNA and DNA
• 3. free oxygen in air drove some life forms to
  extinction and evolved others

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Origin of Eukaryotic Cells

• The endosymbiotic theory proposes that eukaryotic
  cells arose from living communities formed by
  several organisms
• After eukaryotic cells arose, those cells began
  to reproduce sexually
• This enabled evolution to take place at a greater
  rate

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Evolution of multicellualr life forms

• 90 of Earths history occurred during
  Precambrian
• Simple anaerobic forms appeared and were followed
  by photosyntheitc forms which added oxygen to the
  air
• Aerobic forms evolved and eukaryotes appeared
• Early in Paleozoic era the fossil record became
  rich with evidence of many types of marine life
• Life was highly diverse by the first part of
  Paleozoic era

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Cambrian Period

• This is when diversification of life occurred
• Organisms had hard part and first animilia phyla
  evolved
• Trilobites were common

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Ordovician and silurian periods

• Octopus and squid ancestors appeared along with
  aquatic arthropods

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Devonian period

• Animals began to invade the land
• Fish developed the ability to crawl on leglike
  fins
• Fish had jaws, bony skeletons, and scales

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Carboniferous and permian period

• Life expanded over the earths continents
• Other groups of vert evolved from amphibians
• Mass extinction occurred at the end of the
  Paleozoic era
• It affects both plants and animals on land and on
  sea
• 95 of the complex life in the ocean disappeared

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Mesozoic era

• Increase dominance of the dinosaurs
• 1. triassic period-fish, reptiles insects
• 2. jurassic period-dinosaurs dominant
• 3. cretaceous period-reptiles still dominated,
  but another mass extinction occurred

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Cenozoic era

• Mammals evolved adaptations that allowed them to
  live in various environments

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Patterns of evolution

• Macroevolution- large scale change that take
  place over a long time
• There are 6 important patterns to macroevolution
• 1. mass extinction
• 2. adaptive radiation
• 3. convergent evolution
• 4. coevolution
• 5. punctuated equilibrium
• 6. changes in developmental genes

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Mass extinction

• Causes food webs to collapse

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Adaptive radiation

• Unrelated organisms come to resemble one another

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coevolution

• The process by which 2 species evolve in response
  to changes in each other over time
• Ex flowering plants

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Punctuated equilibrium

• Patterns of long stable periods interrupted by
  brief periods of more rapid change