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ORIGINS OF MAMMALS/MASS EXTINCTIONS - Coggle Diagram
ORIGINS OF MAMMALS/MASS EXTINCTIONS
extinction
palaeontologists usually distinguish between normal or background extinction rates and those characterising mass extinctions
extinctions actually occur at all scales with a frequency inversely proportional to their magnitude
mass extinctions almost certainly had some catastrophic cause
the big five mass extinctions
end ordovician
443MYA
85% species
glaciation?
ordovician-silurian
two events killed off
27% families
57% genera
60-70% all species
late devonian
375-360MYA
75% species
several causes?
near Devonian-carboniferous transition
prolonged series of extinctions eliminated about 19% of all families
50% all genera
70% all species
end permian
248MYA
96% species
volcanism?
permian-triassic
earths largest extinction
57% families
83% genera
53% marine families
84 % marine gneera
96% marine species
70% land species including insects
the great dying
end triassic
200 MYA
76% species
several causes?
triassic-jurassic
23% families
48% all genera
20% of marine families
55% marine genera
end cretaceous
66MYA at the cretaceous paleogene transition interval
75-80% species
bolide
Cretaceous-Paleogene
K-T or K-Pg extinction
marine and terrestrial extinctions synchronous
plants, dinoflagellates made it through relatively unscathed
mammals flourished post
about 17% of all families
50% of all genera
can we make any generalizations?/rules governing mass extinctions
mass extinctions tend to occur on both the land and in the sea
on the land plants tend to be more resilient than the animals
certain groups of animals are more susceptible than the others and suffer repeated events
there may be some periodicity of mass extinctions through geological time
periodicity
hypothesis that extinction events have occurred at regular intervals through geological time
emerges from statistical treatment of family range data (much like data used for diversity through time)
random or poisson distribution
waiting times approach an exponential distribution
median waiting time shorter than the average waiting time
regularity implies some organising principle
a set of factors the governs waiting times or
a single ultimate forcing agent with clock like properties
association of periodicity with catastrophism
claimed that a 26 million year period is too long to have been produced by any known terrestrial cause
fischer & Arthur 1977
cenosoix and mesozoic
globerinid species, ammonoid genera and large pelagic predators
no statistical analysis but suggested periodicity of 32MY waiting time
raup and sepkoski 1984
late permian to present day
all marine animal families
removed taxa with extinctions not known accurately, revmoved soft bodied taxa. data set 567 families over 39 Strat. stages
updated timescales
Fourier analysis, autocorrelation and non-parametric randomisation tests
all indicated a significant non-randomness and good fit to a periodic series
lazarus taxa
the proportion of Lazarus taxa permits a rough quantification of the reliability of extinction data within and around critical time intervals
resolution isn't necessarily improved by fine scale studies close to the boundary
need long sequences before and after the event
also need broad geographical range
what factors influence group survival
taxonomic level
groups at higher taxonomic levels are less likely to go extinct than those at lower taxonomic levels
geographic distribution
in a study of the molluscs of the North American Atlantic coastal plain during
normal
periods,
species
with broad geographic ranges were far less likely to go extinction than those with small ranges
during the late cretaceous
mass
extinction, mollusc
families
with large geographic ranges survived better than those with small ranges, even if the individual species within those families had small ranges
ecological generalists tend to survive better
small organisms fare better than larger ones
possible bc larger organisms tend to have Lower reproductive rates
also could be bc larger organisms are more specialised bc they have more critical mechanical design requirements
organisms at higher latitudes tend to fare better
taxa adapted to tropics lack the option of moving towards the equator as temperatures fall
generalists may be more likely to survive than species with great ecological or morphological specialisation
at times of mass extinction contingency plays a big role
what causes mass extinctions
terrestrial (earth-bound) causes
catastrophic upheavals of mountain ranges
correlation between diastrophism and faunal turnover
too localised and not catastrophic enough
need to focus on phenomena that are global in scale causing rapid large changes in the physical environment
changes in sea level and climate
eustatic reduction in sea levels correlate with mass extinctions among marine invertebrates
episodes of vastly elevated volcanism
a tenfold increase in island area results in a doubling of species numbers
regression without mass extinction
quaternary and middle oligocene
followed by rapid transgressions in geologically short time intervals
quaternary faunas likely to have been relatively resistant because they had just survived the environmentally stressful late cenozoic
middle oligocene regression followed closely after a period with elevated levels of extinction
for much of the rest of the Phanerozoic environment changed much more gradually
marine & terrestrial correlate
end cretaceous
reduced sea level
increased land area
end permian
increased land area
more continental climate
end triassic
more continental climate
more extremes of termperature
mass extinctions and climate
plio-pleistocene extinctions of molluscs off the Atlantic coast of USA
high rate of species extinctions in this regions but many fewer on the pacific margins or around the mediterranean
must be water temperature
temperature control hypothesis
many extinction-vulnerable organisms are tropical
tropical organisms are often stenotopic
upwelling of anoxic deeper water onto shelf margins associated with episodes of clomate change
but also associated with marine transgressions
extraterrestrial causes
variations in the heat output from the sun
massive solar flares
supernova - massive influx of cosmic rays
solar system crossing the galactic plane - cosmic rays
collision with bolides
earth should suffer impacts by about six 1km asteroids every 1My and two 10km asteroids every 100My (about 12 large impacts since the beginning of the Phanerozoic)
discovered by accident (Alvarez 1980)
Walter Alvarez sought a “clock” to quantify rates of faunal change around the KT boundary
Although sedimentation rates are highly variable, the rain of dust from space is constant (e.g., 0.0001 g/yr on 1 cm2 of the ocean floor)
Platinum group metals
Relatively inert (unreactive), so remain unchanged in the sediment
Very rare in the Earth’s crust
The amount coming in from space is much greater
Iridium one of the rarest earth elements, but common in space dust
. Can be measured in parts per billion
. Looked for good section of rocks, and measured Ir in clay minerals.
Iridium spike. Causes?
1) Something shut off the production of clay, while the rain of Ir in space dust remained constant.
2) Something boosted the amount of space dust (and hence Ir) by an order of magnitude.
They couldn’t find a reason for #1, so they opted for #2.
But why should space dust go up?
1) A nearby star could have gone supernova, showering the Earth with newly formed elements heavier than iron - among them Ir.
should also find Plutonium (Pu), specifically 244Pu("bomb" Plutonium)
2 more items...
2) The Ir could have come from a mass of extraterrestrial matter arriving in one chunk - as a giant meteor or comet.
Chicxulub crater off the Yucatan Peninsula - From 150 - 300 km in diameter.
3 more items...
Possibly the largest impact known in the world and said by some to be the largest known in the solar system
Right age.
comet impacts
Much rarer than asteroids
Rates could be substantially increased by perturbing the Oort cloud, far beyond the outermost planets (edge 104 astronomical units)
Evidence for periodic extinctions might suggest a more regular and frequent perturbation of the Oort cloud
Passing through the higher stellar densities in the spiral arms might raise collision rates by about 10%.
This would explain short-lived bursts of cometary impacts (1-3My) once every 100My
Triggered by the passage of individual stars
how big a bolide and what effect
An asteroid in the region of 10km in diameter for the end Cretaceous event (the demise of the dinosaurs)
Initially very cold and dark
nuclear winter effect
Cold particularly acute in continental interiors
Less acute in maritime regions (thermal inertia)
Caused by the global dust cloud ejected into the jet stream
Lasted for between 2 and 11 month
May have been sufficient to halt all photosynthesis
Marine and terrestrial food chains would collapse
greenhouse warming
Particularly if the bolide struck the ocean
A huge burden of water vapour would remain in the atmosphere
Could trap infrared radiation reflected back from the earth
Raise global temperatures by 10°C
Duration: 1000 years
Biogeochemical effects
Energy from atmospheric entry and the supersonic plume ejected on entry
Nitric oxides: Rain out as Nitric and Nitrous Acid
direct damage
acid range
indirect damage
mobilisation of trace metals
In 10 years, upper 30m of ocean could have pH reduced to 7.5-7.8
Enough to dissolve calcite and severely stress calcareous organisms
Acid in atmosphere -> exhalation of oceanic CO2
Combines with CO2 in atmosphere (reduced phytoplankton activity)
Greenhouse warming and other palaeoceanographic anomalies would persist for thousands of years.
Palaeontological and geochemical evidence supports a geologically brief but ecologically protracted recovery period, especially in terrestrial plants and marine plankton
Extinction patterns at particular boundaries cannot be read literally
May be a depositional artefact
Artificially gradual extinction patterns result when sampling deteriorates up to a boundary
Stepwise patterns suggest the prior and subsequent impact of cometary fragments
12 Discrete extinction events claimed near the K/T boundary and the extinction of the dinosaurs
Distinct from gradual decline, such as late Cretaceous ammonites, Cenomanian/Turonian boundary and Eocene/Oligocene boundary.
Several physico-chemical phenomena have been proposed as evidence for bolide impacts.
None is diagnostic, but taken together they make a strong case for the end Cretaceous and Late Eocene events.
possible endogenous causes
periodicity itself Is insufficient evidence for extra-terrestrial causes
suggestion that there may be an endogenous cycle of mantle plumes
would need correspondence between the periodicity of paleontological data and independent physics-chemical evidence for impacts or other forcing mechanisms
Mineralogical
Between two and nine intersecting layers of shock lamellae in marine and terrestrial K/T boundary grains
Otherwise known only from nuclear testing sites and impact craters
Occasionally from volcanic eruptions, but K/T has worldwide distribution of large grains
shock metamorphosed quartz
tektites
intense heat and pressure at the impact site produce fragments and spheres of glass
Often ejected over a huge area.
onset and aftermath
greenhouse warming and other palaeoceanographic anomalies would persist for thousands of years
paleontological and geochemical evidence supports a geologically brief but ecologically protracted recovery period esp. in terrestrial plants and marine plankton
extinction patterns at particular boundaries cannot be read literally
may be a depositional artefact
artificially gradual extinction patterns result when sampling deteriorates up to a boundary