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.
recent estimates for extinction rates? - birds and mammals
or birds is one species
extinction per 400 years. [At this rate], no more
than a couple of extinctions should have occurred
in the past 800 years
v Mammals: 1.8 extinctions per million species per year
v Out of 5,500 mammal species, 1 species per 100 years
v What we see is: 43 mammal species went extinct in last 100 years –
43X more than the average rate
v Birds: Extinction of 1 species per 400 years
v Birds: 0ver 190 species since 1500
why is todays extinction rate concerning?
The fact that today’s extinction rate vastly exceeds any
estimation of the background extinction rate impels many
scientists to conclude that we are now on the cusp of the so-
called “Sixth Extinction”
habitat loss in 6th extinction?
v Habitat loss associated mainly with human population growth v Over-exploitation (over- fishing, poaching, soil depletion, alien species introductions, etc. v Global warming & climate v Habitat loss associated mainly with human population growth v Over-exploitation (over- fishing, poaching, soil depletion, alien species introductions, etc. v Global warming & climate change v Global sea-level rise
change v Global sea-level rise
ex of habitat loss -brazil
forest lost to agriculture - forest is fragmented
ice loss ex - greenland
melting of greenland ice sheet 3.8 tril. tons lost 1992-2018 avg in 1992 = 25 bill. tons/yr avg in 2018 - 234 bil./yr may contribute to 7-12 cm sea level rise by 2100
Sea levels attributed to anthropogenic global warming - how much? caused by?
ea level rose 2.0 mm/year for the past 100 years, but since 1990’s it has been rising 3.5 mm per year q Causes include melting of glaciers and thermal expansion of ocean water q Recent studies suggest that the last time atmospheric CO2 levels were as high as today, sea levels were 25-40 m higher than at present (in the Miocene, >20 MYA)
summary of current climate effects
v Habitat loss associated with human population growth, agriculture, deforestation, urbanization, recreation, etc. v Over-exploitation (over- fishing, poaching, invasive species introductions, soil depletion, etc.) v Global warming & climate change: droughts, storms, changing ocean currents, decreased solar reflectance, thawing permafrost, methane release, ocean turnover v Sea-level rise: melting ice caps, thermal expansion, uneven gravitational effects
species red list?
- Staghorn Coral
- Ringed Seal
- Leatherback Turtle
- Emperor Penguin
- Quiver Tree
- Clownfish
- Arctic Fox
- Salmons
- Koala
- Beluga Whale
