mass extinctions Flashcards
•
Mass extinction end of ordovician
-~443 mya
- Lost: ~57% of genera; ~86% of species
- Onset of alternating glacial & interglacial
episodes
- Repeated marine transgressions &
regressions
- Uplift of Appalachian mountains affecting
atmospheric & ocean chemistry
- Mass extinction end of devonian
- ~359 mya
-Lost: ~35% of genera; ~75% of species- Global cooling followed by global warming
-Wide-spread deep-water anoxia - Bolide impacts – timing & importance still
Debated
- Global cooling followed by global warming
end-Permian mass extinction
~251 mya
– Lost: ~56% of genera; ~96% of species
– Several orders of insects; ~54% of marine families
– Dominant amphibians & therapsids replaced by new therapsids & diapsids
– Pangaea – single large supercontinent
Ø Disruption of seawater circulation -> depletion of O2 ; high conc. of CO2->
change in climatic pattern, global warming
– Massive volcanic eruptions in Siberia -> release of toxic gases
- Mass extinction: end of triassic
- Approx 2 mya
- Lost approx 47% of genera: 80% of species
- Elevated co2 levels causing increased global temps
Cret
~65 mya
v Lost: ~40% of genera; ~80% of species
v Extinctions of non-avian dinosaurs, marine reptiles,
cephalopods, foraminiferans, some terrestrial
mammals, temperate zone plants
v Not appearing to be as affected were tropical plants,
small animals, and freshwater organisms
Cretaceous extinction: why?
- Deccan Traps – Large igneous rock formation on Deccan Plateau of west-central India – Started to form about 66 mya leading to huge volcanic eruption – Lava flow covered ~1.5 mil. Km 2 (half the size of modern India) – Releasing huge amount of volcanic ash, especially SO 4 – Temp. dropped by ~20°C
climate change, periodic extinction in cretaceous?
Climate change? – Inland seas regressed – Cooling – Periodic extinction Ø Natural event Ø Every 26-30 million years due to diversity fluctuations
creteceous - define kt boundRY
– K-T boundary Ø Cretaceous-Tertiary boundary; recent name: Cretaceous- Paleogene (K-Pg) boundary Ø A geological signature Ø A thin band of dark-coloured rock Ø ~65 million years old
k-t boundary sites?
colorado, trinidad, montana, southern alberta
Modern impact hypothesis for cret. ?
Luis & Walter Alvarez
– Iridium - rare on Earth, relatively common in
meteorites
– At K-T boundary, levels of iridium are 20-160
X normal levels
– Concluded that iridium left by impact of
asteroid at the end of Cretaceous
– Alvarez, L, W. Alvarez, F. Asaro, & H. Michel.
– Yucatan Impact Crater Ø Beneath several km of sediment was large impact crater (>180 to 300 km) possibly created by a direct impact with an asteroid ~10 km wide!! Ø Shocked quartz from Mexico, Haiti and around Caribbean Ø Evidence of tsunami - tidal wave 1-5 km high - wave moved boulders (16 ft in diameter in Arkansas), Texas, Cuba (900 miles away it was still 1500 ft high)
• Late Pleistocene Extinction
• 6th mass extinction • 11kya Was it climate change? or overkill (by human hunters), or hyper-disease, or an extraterrestrial impact? Extinction events seem to coincide with human arrival in North America, Australia, New Zealand,
sp. that went extinct in late pleisto.?
Mammoth Giant ground sloth Saber-toothed cat also mastodon, camels, horses, etc • Loss of predators - top down effect - loss of habitat and other species
recent human caused extinctions?
†Dodo (1681), †Steller’s sea cow (1768), †Great Auk (1852), †Passenger Pigeon (1914
•
• More recent human-caused extinctions: †Quagga (a type of South African zebra) 1883; Thylacine (Tasmanian tiger) 1930’s; Bali tiger (1950’s) and other subspecies of tiger
who is martha?
last survivor of passenger pigeon, died in 1914
what kind of extinctions occur now? what is characteristic of them?
Background extinctions are at the opposite end
of the spectrum from mass extinctions. It is
generally assumed that “natural” extinctions go
on all the time, but at very low or “background”
rates. Characteristic of background extinctions is
that they occur in a random or uncorrelated
manner.
