The History of Life on Earth

1
The History of Life on Earth

• Chapter 25.2 and 25.4

2
Fossil Record

• Found in diverse environments
• Sedimentary rock
• petrified (stone) trees
• molds left in stone
• preserved organisms in amber
• preserved bodies in areas with little
  decomposition (frozen in ice, in acid)

3
Fossil Dating

• Relative Dating
• fossils are frozen in time
• Compare similar strata of rock to obtain a
  relative date
• Geological Time Scales are established
• Four Eras
• Precambrian
• Paleozoic
• Mesozoic
• Cenozoic

4

• Radiometric Dating (Absolute Dating) gives a more
  exact age for the fossil
• Uses radioactive isotope half-lives
• Dating using L-amino acids and D-amino acids
• Only L-amino acids are associated with living
  organisms.
• After death, both L and D amino acids can be
  measured
• Fossil record is incomplete and imperfect!

5
Continental Drift

• Earths history explains geographical
  distribution of species
• Continental drift has influenced major
  evolutionary events
• 250 mya all land masses converged into Pangaea
• Drifting of continents helps explain
• marsupials of Australia
• matching fossils in Brazil and West Africa

6
Major Adaptive Radiations

• Evolve novel characteristic
• Novel characteristic opens an adaptive zone
• Animal evolution of hard body may have led to
  Cambrian explosion
• Mammals with unique novelties did not diversify
  until dinosaurs opened up the adaptive zone to
  them

7
Major Extinctions

• Permian extinction - coincides with Pangaea
• Cretaceous extinction - loss of dinosaurs
• May have been caused by asteroid

8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11

• C14 has a half-life of 5600 years. How many
  years will it take a sample that began with 8g of
  C14 to have 2g left?
• Converting 8g to 4 g is one half life.
• Converting 4g to 2g is 2 half lives.
• Therefore it will take 2 half lives or 5600 x 2
  11,200 years.

12
(No Transcript)