Download Precambrian - Cambrian Eukaryotes

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
Adaptation, not maladaptation
• No mechanism for maladaptation
• Natural selection increases, not decreases,
fitness
• Species aren’t organisms - no programmed
“species death” and no mechanism for
“weak genes”
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
Examples
• High extinction and speciation:
– Mammals (E=0.71/my, S=0.93/my)
– Also trilobites, ammonites, graptolites
• Low extinction and speciation
– Clams (E=0.09/my, S=0.15/my)
– Nautiloids
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
Mass Extinction Causes
• Coincidence
• Physical causes:
– changes in climate
– Salinity
– living space: reduction in continental shelf
space due to plate motions or regression
Mass Extinction Causes
• Coincidence
• Physical causes
• Biological causes: competition, predation
Mass Extinction Causes
•
•
•
•
Coincidence
Physical causes
Biological causes
Catastrophe: impact, volcanoes
Permo-Triassic extinction
• Coincidence?: Over 90% of life dies, so
definitely real
Permo-Triassic extinction
• Coincidence? No
• Physical: Continental configuration and
regression
– Reduced continental shelf space
– Glaciation
– Severe climate
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.)
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
Permo-Triassic extinction
• Coincidence: No
• Physical: Continental configuration and
regression
• Biological: Appearance of biological
“bulldozers”
• Catastrophe:
– Impact? Probably not
– Volcanoes (Methane hydrates)
Flood Basalt effects
• Increased carbon dioxide and global
warming
• Acid rain from sulphur
• Release of methane hydrates from ocean
floor
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
Permian
• Sooo…
– It’s complicated - plenty of instability: physical,
biological and disaster
– Insufficient evidence yet to point to a single
cause
Cretaceous-Tertiary Extinction
• Coincidence:85% species extinction, so it’s 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
K/T Catastrophe
• Impact hypothesis
• Volcanic hypothesis
Impact scenario
• Asteroid about 10 km (6 mi.) struck,
probably in Yucatan at Chicxulub
Impact scenario
• Asteroid about 10 km (6 mi.) struck,
probably in Yucatan at Chicxulub
• Immediate heat shock and wildfires near
impact site
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
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
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
Evidence
• Crater at Chicxulub
Evidence
• Crater at Chicxulub
• Iridium spike
Asteroids have higher
iridium abundance than
Earth’s crust. Iridium of
Earth is mostly in the
mantle and core.
Evidence
• Crater at Chicxulub
• Iridium spike
• Shocked quartz
Two directions of
lamellae typical of
impacts
Evidence
•
•
•
•
Crater at Chicxulub
Iridium spike
Shocked quartz
Tektites
Glass globules from
melting of surface and
striking object
Evidence
•
•
•
•
•
Crater at Chicxulub
Iridium spike
Shocked quartz
Tektites
Soot
Carbon in boundary clay
from wildfires
Evidence
•
•
•
•
•
•
Crater at Chicxulub
Iridium spike
Shocked quartz
Tektites
Soot
C-13 indicates
catastrophic extinction
Biological effects: predictions
• Who dies?
– Planktonic orgs.
– Ocean surface
ecosystem
– Orgs. with poor
thermoregulation
• Who lives?
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
Biological
effects
• Who actually dies?
–
–
–
–
–
–
Planktonic forams
Marine reptiles
Ammonites
Dinosaurs
Birds
Non-flowering
plants
– Marsupials
Biological
effects
• Who actually lives?
– Bottom communities:
clams, snails,
crustaceans, etc.
– Placental mammals
– Angiosperms
– Amphibians
– Turtles
– Insects
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