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Mass Extinctions: The Role of Extra-terrestrial Factors, Slides of Theory of Evolution

The causes and effects of one of the most catastrophic events in earth's biosphere: the end cretaceous mass extinction. The evidence for the causes, including the role of iridium spikes in sediments and the possible theories of volcanic activity, supernova, and meteor impact. It also covers the effects of a meteor impact on the planet, such as shock waves, debris clouds, and lowered solar radiation. The document also touches upon the cyclical nature of mass extinctions and the controversial theory of an extra-terrestrial cause, such as planet x or a brown dwarf star.

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Uploaded on 01/02/2013

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Lecture 23: Mass Extinctions
5.) Cretaceous (144 - 65 mya)
•Mesozoic : (Permian → Cretaceous) huge ↑ in
biodiversity
•End Cretaceous (65 mya): 85% of all spp. gone
•All non-avian dinosaurs & pterosaurs gone
•No terrestrial organisms >25 kg survive!
•Relatively unaffected: crocodiles, lizards,
turtles, mammals, birds
Cause: Iridium??
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Lecture 23: Mass Extinctions

5.) Cretaceous (144 - 65 mya)

  • Mesozoic : (Permian → Cretaceous) huge ↑ in

biodiversity

  • End Cretaceous (65 mya): 85% of all spp. gone
  • All non-avian dinosaurs & pterosaurs gone
  • No terrestrial organisms >25 kg survive!
  • Relatively unaffected: crocodiles, lizards,

turtles, mammals, birds

Cause: Iridium??

Alvarez et al. (1980)

  • spike in levels of Iridium in sediments ~ 65 mya
  • Ir in core; rare in surface rock
  • common in space dust
  • 3 Ho for IR spike :
  1. volcanic activity?
  2. supernova?
  3. meteor impact?

Effects of a Meteor Impact

  • Shock Wave: fires, earthquakes
  • Debris Cloud: years of acid rain, dust,

“nuclear winter”

  • Lowered solar radiation reaching earth:

cold & dark → ↓ 1 ° productivity

  • Nickel Poisoning : effectively kills PSIS

Yucatan Peninsula (Chicxulub)

  • “Smoking Gun” :

impact crater

  • ~ 10 km meteor

(crater ~ 150 km diam.)

  • cause or “coup de

grace?”

Extra-terrestrial Cause?

Suggested by periodicity:

  • Planet X (“Nemesis”):
  • Brown Dwarf (star that didn’t reach ignition

mass) or Planet from another system

  • Passes through Oort comet cloud
  • Sends meteors to earth every 26 my
  • Controversial!!

Background vs. Mass Extinctions

Signor - Lipps effect:

  • Mass extinction may appear gradual:
  • Orgs. disappear from the fossil record at diff. times
  • Rare orgs less likely to be found in latest deposits even if they survived as long as common ones

Converse:

  • Gradual extinction may appear mass
  • Pseudoextinctions etc.

Surviving Mass Extinctions

  • Surviving spp. more likely to be generalists
    • can adjust to Δ’s in conditions
  • “Iterative Evolution”: forms “re-evolve” during

Adaptive Radiations after mass extinctions

  • B/w mass extinctions: Spp.-Rich Clades survive

background extinction better

  • “Bad Genes or Bad Luck?”