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
