Lec 13: Diversification - Mass extinction events Flashcards
what are the limitations of using the fossil record to estimate background rate of extinction?
- doesnt accurately represent past diversity
- fossil formation not possible in all environments
- soft-bodied organisms don’t preserve well
what are chronospecies
species that change over a long time scale
at which taxonomic level are extinction rates measured?
family, because it’s hard to tell differences between species in the fossil record
what are biotic mechanisms of extinction?
- a predator expands its range
- the organism a species exploits comes up with an unbeatable defense
- can be beat by its competition
- disease
what are abiotic mechanisms of extinction?
the niche or habitat can no longer support the species:
- volcanoe
- climate change
- sea level change
- impact events
what is a mass extinction?
a mass extinction is the extinction of a large number of unrelated species, that occurs globally over a short period of time
name the 5 mass extinctions in history?
late:
- ordovician (440)
- devonian (375)
- permian
- triassic
- cretaceous
which type of organism suffered the most during the late ordovician extinction
marine organisms!
What caused the late-ordovician extinction, and why was this such a big deal?
- COOLING and sea level fall
- most species on earth were adapted to warm, shallow waters, and could not survive in cold, deep waters
what physical mechanisms led to the late-ordovician extinction?
- plate tectonics –> land moved to south pole –> glaciers formed –> sea levels fell
when did the late-ordovician extinction occur?
440 Ma
what is the devonian referred to as?
the age of fishes
what are theories behind the late-devonian extinction?
reduction of atmospheric co2 and subsequent cooling through either:
- rapid reduction in atmospheric CO2
- the depletion of CO2 by plants (which expanded onto land during this period)
when did the late-devonian extinction occur
375 million years ago
what is the largest of all known mass extinctions?
the late-permian extinction
what is the late-permian extinction referred to as?
the great dying
the late-permian extinction occured…
250 million years ago
what caused the late permian extinction?
1) a series of volcanic eruptions
2) released CO2
3) atmosphere heated up and ocean acidified
4) aerosols blocked out sunlight = cant do photosynthesis + acid rains
when did the late-triassic extinction occur?
200 million years ago
How did the triassic extinction affect dinosaurs?
it opened up niches on land, allowing dinosaurs to dominate during the ensuing Jurassic
what are the speculated causes of the triassic extinction
asteroid impact or massive volcanic eruption (because high levels of mercury in triassic rocks
when did the late cretaceous extinction occur
66 million years ago
what did the late cretaceous kill?
dinosaurs! and all large tetrapods
what caused the late-cretaceous extinction?
1) comet or asteroid
2) dust and ash
3) no sun
4) global winter
5) no photosynthesis –> plants and plankton die –> extinction moves up food chain
possibly also caused by volcano
what is the press pulse theory?
the combination of sudden catastrophes with steadier pressures on species leads to a greater impact on the environment.
why do scientists believe we are currently in the 6th mass extinction?
extinction rates are 100 to 1000x the natural background extinction rate
what are some examples of planned extinction by humans?
- passenger pigeons (hunting)
- smallpox (immunization)
- CRISPR
