Extinction - Mass Extinction Events

Question 1

How many known major mass extinctions events?

Answer 1

• 5 at irregular intervals

Question 2

What are the indirect and direct causes associated with the five major mass extinctions?

Answer 2

• climate change linked to all five (directly or indirectly)

Direct causes:

• rapid temp changes
• changes in sea level

Indirect causes:
- drivers such as asteroid impacts, volcanic eruptions , etc impact climate.
L>Rapid temp changes and changes in sea level the occur (driven by outside forces)

Question 3

Which two mass extinctions are best understood for their causes?

Answer 3

• K-T

- O-S

Question 4

List the major mass extinctions in order of oldest to youngest.

Answer 4

1. Ordovician-Silurian Extinction (440mya)
2. End-Denovian (365 mya)
3. End-Permian (Permian -Triassic; 250mya)
4. End-Triassic (200mya)
5. Cretaceous-Tertiary (K-T; 65mya)

Question 5

Explain the Ordovician- Silurian Extinction

Answer 5

• life existed in the seas , mostly benthic
• 1/2 of all genera disappeared
• possible causes: sudden shift in Earths climate from greenhouse to icehouse conditions due to Gondwanaland passing over pole, eld to large temp changes in ocean, drastic drop in sea level via ice forming
• Surviving lineages diversified and overall marine diversity slowly recovered

Question 6

Describe the End-Devonian extinction.

Answer 6

• land was colonized: plant diversification, shark and bony fishes appear in fossil record
• extinctions largely contained to marine organisms (20% of marine families disappeared)
• Cause: plant colonization of land -> CO2 uptake from atmosphere -> global cooling, major cooling event led to climate change, causing mass extinctions, may have actually been a series of smaller extinction evens in succession

Question 7

Describe the End-Permian / Permian-Triassic extinction.

Answer 7

• WORST
• 50-70% terrestrials sp lost, mostly plants
• Cause? Switch from icehouse to greenhouse via maybe massive volcanism, methane out-gassing from sediments -> release of CO2 -> Global warming + acid rain -> terrestrial extinctions
• rapid warming eld to shutdown of thermohaline circulation = anoxia in deep water leading to many marine extinctions too
  L>marine fauna went from 100+sp to less than 6 sp

Question 8

Explain the End-Triassic extinction.

Answer 8

• 50% of all sp disappeared: mainly large terrestrial animals (esp large amphibians), plants and marine species: paved way for dinosaur diversification
• Cause: unknown (gradual climate change, volcanism, asteroid?)

Question 9

Explain the Cretaceous-Tertiary (K-T) extinction.

Answer 9

• extinction of almost all large tetrapods very rapidly: mammals, most dinosaur linages, pterosaurs, lizards, insets; extinction of marine species: plesiosaurs, marine lizards, sharks, fishes, mollusks and planton
• Cause? One or more asteroid impacts (Chicxulub crater , Mexico. Another near India around the same time), led to rapid wide scale extinction via increase in infrared radiation…other extinctions followed via starvation (loss of sunlight/ cooler planet)

Question 10

Explain the pattern of events of an asteroid impact

Answer 10

1. Impact event
2. Particulates enter atmosphere (if ejecta reaches far enough, can return to earth and release massive amounts of infrared radiation, burning veg)
3. Particulates in a atmosphere block sunlight / cool planet for months -> centuries
4. Climate change + decreased sunlight -> large scale vegetation changes
5. Many animals go extinct (loss of food source), but not all levels of food web are equally impacted
   L>generalists are more likely to survive

Question 11

Explain the loss of life following the impact event in the Cretaceous-Tertiary extinction

Answer 11

• followed typical asteroid impact pattern
• larger sp went extinct, smaller ones survived (could take shelter from radiation/fires)
• water dwelling larger sp survived (crocodiles and turtles ex) while strictly terrestrial ones went extinct
• dinosaurs were dom large animal on lang, went extinct (except for avian lineage)
• smaller organisms and omnivores survived while large herbivores and top predators disappeared

Question 12

what about minor extinction events?

Answer 12

• many have occurred through time

Question 13

What is the common factor for all extinction’s ?

Answer 13

• climate is the common factor !!

How:

• climate change = regional events into global catastrophes
• asteroid impacts/ volcanic eruptions -> massive amounts of particulate into atmosphere
• particulates intercept incoming solar radiation, cooling effect
• multiple volcanic events/ asteroid impacts = major global cooling -> extinctions (large animals, ectotherms, land plats sensitive to freezing)
• if cooling is extreme, plants and animals can’t match velocity of climate change
• decrease in sea level -> devastate continental shelf habitats, eliminate shallow seas = extinctions

Question 14

What is the 6th mass extinction?

Answer 14

• of the ~4 billion sp o Earth, ~99% have gone extinct
• species diversity increases over time
• extinctions balanced out by speciation events
• current extinction rates are much larger than background extinction events (Ceballos et al 2015)
• documented # extinctions likely underestimation (most sp not formally described)
• over the last 350 years, highest extinction rates are on islands (via mainly habitat loss and invasions)
• current mass extinction vent predicted to eb result of mainly human related factors..but esp due to impact of climate change and its interaction with other factors
• biodiversity recovery following mass extensions can aka millions of years..time scale humans will not benefit from recover

Question 15

What are examples of human mediated extinctions?

Answer 15

• co-opting resources from other organisms
• habitat fragmentation
• spread of invasive species
• spread of pathogens
• directly killing sp (hunting etc)
• impacts of climate change