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

Potential Triggers Asteroid Impacts = sudden

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

Periodic Comet Strikes Fossil record shows some 26-27 million year period of some extinction event (usually small) Nemesis Theory (likely not correct) On the time scale of 20-30 million years (1/10 of our galactic orbit) – nearby stars could perturb our Oort cloud of Comets

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.

Five Agreed Upon Major Events

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

New Evolutionary Niches Open The Rats Become the Kings

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

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