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Patterns of Evolution
Unit 6
Powerpoint #2
1) Mass Extinction
 When many different species of
organisms go extinct at the same time.
 End of Paleozoic: 95% of complex life
(both plants and animals on the land
and in the sea) went extinct.
Diversity of life & periods of mass extinction
Fossil Evidence of Mass Extinction
 Fossilization does not happen very often.
 Mass Extinctions also do not occur very
 Scientist believe that there are more fossils
to be found around the time of mass
extinctions than any other time.
Geologic Time
Based Upon major changes in the fossil
record in the rock strata
ERAS are longer time divisions than PERIODS
There are four eras:
Precambrian (4.6 billion – 544 million years ago)
Paleozoic (544 - 245 million years ago)
Mesozoic (245 – 65 million years ago)
Cenozoic (65 million – Present)
Cretaceous extinction
The Chicxulub impact crater in the Caribbean Sea
near the Yucatan Peninsula of Mexico indicates an
asteroid or comet struck the earth and changed
conditions 65 million years ago
Early mammal evolution
 125 mya mammals
began to radiate
out & fill niches
From sea to land
Causes of Mass Extinction
 Climate Change: rapid changes in yearly weather
patterns. Example: Ice Age
 Volcanism: the sudden oozing of millions of cubic
meters of lava from the earth that release gasses
poisoning the atmosphere
 Impact Events: Meteors or asteroids impacting the
2) Adaptive Radiation
(Divergent evolution)
 A single species, or small group, evolves, through
natural selection into diverse forms.
Darwin’s Galapagos
Divergent Evolution
 Organisms with a common ancestor develop
many differences over time.
3) Convergent Evolution
 When unrelated organisms come to resemble
each other due to environmental demands.
Placental v. Marsupials
4) Coevolution
 When two species
evolve in response
to changes to each
other over time
Insects and
5) Punctuated Equilibrium
 Long stable periods interrupted by periods of
rapid change.
6) Gradualism
 Small genetic changes occurring slowly
within a population