1. Evidence for Many Events over Geological History
Mass Extinctions
Evidence for Many Events over Geological History

2. Potential Triggers
Asteroid Impacts = sudden

3. Large Basalt Outflows
Large CO2 changes which can affect atmospheric and ocean chemistry (slow)

4. Periodic Comet Strikes
Fossil record shows some million year period of some extinction event (usually small)
Nemesis Theory (likely not correct)
On the time scale of million years (1/10 of our galactic orbit) – nearby stars could perturb our Oort cloud of Comets

5. At least a dozen significant events
The concept of impact induced extinction events is relatively new – first evidence came in 1980 regarding the KT event (65 million years ago – dead dinosaurs).
Further research and data have now shown that such events are common.

6. Five Agreed Upon Major Events

7. Periodic (?) Extinctions of Varying Amplitude (percent extincted)
Relatively stable

8. New Evolutionary Niches Open
The Rats Become the Kings

9. Implications
External disruption changes the ecosystem survival rules and therefore changes evolutionary pathways
Random large scale catastrophes can reset both the evolutionary clock and the evolutionary timescale
This is been a very important component of species evolution on Earth

10. Implications II Evolutionary Clock gets reset
Life recovers (relatively rapidly) to fill new ecological niches  this empowers species diversification
This means that “survival of the fittest” doesn’t work on long timescales  random catastrophe important