Periodic Extinctions Have Been the Rule for Life on Earth

• Extinction has been wide spread.– Cambrian -

• 80% of families -• > 90% of species

– Permian - • 60% families• 90% species

– Cretaceous - • 20% families• > 50% species

Is it possible that life has not been a process of ever expanding

diversity?• Could speciation

and diversification be a process of periodic extinction and subsequent reradiation?

So How Old is the Earliest living Organism?

Gunflint Chert in Banded Iron formation -- Lake Superiorabout 1.9 b.y. old

Stromatolites - bacterial tuftsWestern Australia & elsewhere

Contain fossilbacteria (cyanbobacteria)3.5 - 4.0 b.y. old

For many years 5 kingdom system held

• New Techniques have discovered much more diversity, leading to revision of classification

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