Geologic Time Scale and Introduction to Extinctions
divides 4.5 billion years of Earth history into time periods
many divisions are based on extinction events
followed by radiation of the new species
precambrian is 87% of Earth’s history
99% of all species that ever lived are extinct
this is considering 3.8 billion years of life on Earth
there are still around 1.8 million known species and an estimated 5-15 million species (sources vary) on Earth
extinctions are normal
extinction is the expected fate, not the rarity
the current rate of extinction isn’t normal
1000 times the background rate
must meet 3 criteria:
30% of species are extinct
broad range of ecosystems
short/sudden (<1 million years)
classified by severity:
major: 80-95% of species extinct
intermediate: 50% of species extinct
minor: 30% of species extinct
at least 5 in the Phanerozoic
End-Ordovician
Late Devonian
Permo-Triassic (End-Permian)
End-Triassic
End-Cretaceous (Cretaceous/Paleogene)
Permo-Triassic is a major mass extinction, all others are intermediate
divides 4.5 billion years of Earth history into time periods
many divisions are based on extinction events
followed by radiation of the new species
precambrian is 87% of Earth’s history
99% of all species that ever lived are extinct
this is considering 3.8 billion years of life on Earth
there are still around 1.8 million known species and an estimated 5-15 million species (sources vary) on Earth
extinctions are normal
extinction is the expected fate, not the rarity
the current rate of extinction isn’t normal
1000 times the background rate
must meet 3 criteria:
30% of species are extinct
broad range of ecosystems
short/sudden (<1 million years)
classified by severity:
major: 80-95% of species extinct
intermediate: 50% of species extinct
minor: 30% of species extinct
at least 5 in the Phanerozoic
End-Ordovician
Late Devonian
Permo-Triassic (End-Permian)
End-Triassic
End-Cretaceous (Cretaceous/Paleogene)
Permo-Triassic is a major mass extinction, all others are intermediate