What causes extinction?

1
What causes extinction?

• Old explanations
• Maladaptation - organisms evolved poorly-adapted
  features
• Racial senescence - species became weak over
  time
• Discuss the likelihood of these explanations with
  your table

2
Adaptation, not maladaptation

• No mechanism for maladaptation
• Natural selection increases, not decreases,
  fitness
• Species arent organisms - no programmed species
  death and no mechanism for weak genes

3
Is everyone equally vulnerable to extinction?

• Generalists v. specialists
• Relationship between extinction and speciation
  rates
• Organisms that speciate readily also tend to have
  short species duration - high speciation and high
  extinction rates go together
• Talk at your table about what would cause high
  speciation rates

4
Examples

• High extinction and speciation
• Mammals (E0.71/my, S0.93/my)
• Also trilobites, ammonites, graptolites
• Low extinction and speciation
• Clams (E0.09/my, S0.15/my)
• Nautiloids

5
Mass Extinction Causes

• Coincidence lots of organisms happened to die at
  the same time. Can be ruled out statistically.
• Need to be especially cautious if the species
  that go extinct are unstable groups
• More persuasive if stable groups also suffer
  extinction

6
Mass Extinction Causes

• Coincidence
• Physical causes
• changes in climate
• Salinity
• living space reduction in continental shelf
  space due to plate motions or regression

7
Mass Extinction Causes

• Coincidence
• Physical causes
• Biological causes competition, predation

8
Mass Extinction Causes

• Coincidence
• Physical causes
• Biological causes
• Catastrophe impact, volcanoes

9
Permo-Triassic extinction

• Coincidence? Over 90 of life dies, so
  definitely real

10
Permo-Triassic extinction

• Coincidence? No
• Physical Continental configuration and
  regression
• Reduced continental shelf space
• Glaciation
• Severe climate

11
Permo-Triassic extinction

• Coincidence? No
• Physical
• Continental configuration and regression
• Biological Appearance of biological
  bulldozers
• Shallow burrowers
• Earlier life was immobile bottom dwellers
  (brachiopods, bryozoans, crinoids, etc.)

12
Permo-Triassic extinction

• Coincidence? No
• Physical Continental configuration and
  regression
• Biological Appearance of biological bulldozers
• Catastrophe
• Impact? Probably not
• Lack of tektites, shocked quartz
• Some iridium, but not enough

13
Permo-Triassic extinction

• Coincidence No
• Physical Continental configuration and
  regression
• Biological Appearance of biological bulldozers
• Catastrophe
• Impact? Probably not
• Volcanoes (Methane hydrates)

14
Flood Basalt effects

• Increased carbon dioxide and global warming
• Acid rain from sulphur
• Release of methane hydrates from ocean floor

15
Testing the volcanic hypothesis

• For volcanic hypothesis to be credible
• Eruptions must predate the extinction
• Extinctions must not be instantaneous
• Expect to see pulses of extinction as disaster
  intensifies

16
Permian

• Sooo
• Its complicated - plenty of instability
  physical, biological and disaster
• Insufficient evidence yet to point to a single
  cause

17
Cretaceous-Tertiary Extinction

• Coincidence85 species extinction, so its real
• No big physical changes - many small continents
  with lots of shelf space, mild climate
• No big biological changes preceding the
  extinction, no big change in ecological structure
  of the oceans after the extinction
• That only leaves catastrophe

18
K/T Catastrophe

• Impact hypothesis
• Volcanic hypothesis

19
Impact scenario

• Asteroid about 10 km (6 mi.) struck, probably in
  Yucatan at Chicxulub

20
Impact scenario

• Asteroid about 10 km (6 mi.) struck, probably in
  Yucatan at Chicxulub
• Immediate heat shock and wildfires near impact
  site

21
Impact scenario

• Asteroid about 10 km (6 mi.) struck, probably in
  Yucatan at Chicxulub
• Immediate heat shock and wildfires near impact
  site
• Particulates of gypsum (Ca2SO4) cause acid rain,
  killing plankton

22
Impact scenario

• Asteroid about 10 km (6 mi.) struck, probably in
  Yucatan at Chicxulub
• Immediate heat shock and wildfires near impact
  site
• Particulates of gypsum (Ca2SO4) cause acid rain,
  killing plankton
• Particulates create clouds, block sun, killing
  plants

23
Impact scenario

• Asteroid about 10 km (6 mi.) struck, probably in
  Yucatan at Chicxulub
• Immediate heat shock and wildfires near impact
  site
• Particulates of gypsum (Ca2SO4) cause acid rain,
  killing plankton
• Particulates create clouds, block sun, killing
  plants
• Temperature drops, killing organisms with no
  tolerance for cold

24
Evidence

• Crater at Chicxulub

25
Evidence

• Crater at Chicxulub
• Iridium spike

Asteroids have higher iridium abundance than
Earths crust. Iridium of Earth is mostly in the
mantle and core.
26
Evidence

• Crater at Chicxulub
• Iridium spike
• Shocked quartz

Two directions of lamellae typical of impacts
27
Evidence

• Crater at Chicxulub
• Iridium spike
• Shocked quartz
• Tektites

Glass globules from melting of surface and
striking object
28
Evidence

• Crater at Chicxulub
• Iridium spike
• Shocked quartz
• Tektites
• Soot

Carbon in boundary clay from wildfires
29
Evidence

• Crater at Chicxulub
• Iridium spike
• Shocked quartz
• Tektites
• Soot
• C-13 indicates catastrophic extinction

30
Biological effects predictions

• Who dies?
• Planktonic orgs.
• Ocean surface ecosystem
• Orgs. with poor thermoregulation

• Who lives?

31
Biological effects predictions

• Who dies?
• Planktonic orgs.
• Ocean surface ecosystem
• Orgs. with poor thermoregulation

• Who lives?
• Bottom dwellers who eat dead things
• Orgs. with dormancy capability

32
Biological effects

• Who actually dies?
• Planktonic forams
• Marine reptiles
• Ammonites
• Dinosaurs
• Birds
• Non-flowering plants
• Marsupials

33
Biological effects

• Who actually lives?
• Bottom communities clams, snails, crustaceans,
  etc.
• Placental mammals
• Angiosperms
• Amphibians
• Turtles
• Insects

34
Volcanic hypothesis

• Huge volcanic eruption produces climatic change,
  acid rain
• Volcanoes bring up iridium
• BUT
• Problems demonstrating that the eruption is the
  right age
• Basaltic eruptions usually produce little ash, so
  little climate change