MASS EXTINCTIONS Flashcards
Definition of mass extinction
Mass extinction - a massive decline in the number of different species, over a short period of time (Ma)
- 5 major events during the phanerozoic
- we’re living through 6th extinction, caused by human activity
Great oxygenation event - appearance of oxygen
occurred during the precambrium
- early earth had no oxygen in atmosphere or oceans
- early life (bacteria) produced energy using chemical reactions near hydrothermal vents
- cyanobacteria evolved and photosynthesised, producing oxygen as waste
- cyanobacteria formed layered moulds called “stromatolites”
Great oxygenation event - part 2
- oxygen was toxic to most life
- oxygen released into sea water combined with dissolved Fe²+ to produce solid iron oxide which sunk, forming layers (banded iron formations)
- oxygen production from cyanobacteria continued, even after all dissolved Fe²+ had precipitated, so oxygen escaped into atmosphere permanently changing its composition
- this triggered global cooling, leading to snowball earth
Albedo effect
Positive feedback loop
- ice sheet forms
- snow reflects high % of light energy
- less light absorbed as heat energy
- lowered temperature causes more ice to form
Ordovician - Silurian mass extinction
Occurred 443Ma
- Gondwanaland was in southern hemisphere, South Pole was in North Africa
- huge ice sheet formed
- Albedo effect cooled climate
- sea levels fell as water became snow/ice on land
- loss of shallow shelf environments (diagram 7)
- lead to changing ocean chemistry - increased lead, arsenic and iron:
-malformed plankton
-affected trilobites, graptolites
and brachiopods
-deformities in microfossils
Permo - triassiac mass extinction
AKA end permian
252Ma - marks end of Palaeozoic
- 95% of marine species affected
-trilobites, tabulate + rugose
corals, most brachiopods
went extinct - 50% of all animal families extinct
- plants and insects extinct
Permo - triassic theory: pangaea formed
Formation of pangaea:
- extreme continental climate
-arid, no rain, hot - fewer rivers due to climate
- fewer rivers due to being a single land mass
- loss of shallow shelf sea habitats
-parts of pangaea were polar
-glaciations cause sea levels to
fall
Permo - triassic theory: siberian traps
- major mantle plume (triggered by bolide - shocked quartz of same age found in Australia)
massive volcanic activity - flood basalts of the siberian Large Igneous Province (LIP)
- lava flow, pyroclastic flow, ash
- stratospheric ash + gas:
-globally redistributed fast
-blocked sun causing reduced
photosynthesis
-global cooling over thousands
of years
-greenhouse gases released
-SO² + H²0 formed acid rain
which damaged plants and
acidified shallow water
Permo - triassic theory: methane hydrates
Solid crystalline lattice containing CH⁴ (usually in marine sediment)
Positive feedback loop:
- hydrates become unstable if water temperature rises
- methane gas is released
- causes global warming
Cretaceous - Tertiary mass extinction
AKA Cretaceous - Palaeogene
Occurred 66Ma
- belemnites, ammonites, dinosaurs extinct
- bivalves and fish families affected
- 17% of all families extinct
Cretaceous - Tertiary theory: impact event
- bolide - iron meteorite
- 180km crater in Yucaton, Mexico
-iridium present
-shocked quartz - ejecta from
impact
-tektites - frozen drops of
melted rock - impact created mega tsunami (sediment evidence in Texas)
- water was underlain by limestone + gypsum leading to CO² + SO² being released
- global cooling (nuclear winter) followed by global warming
- wildfires
-charcoal layer all over planet
Cretaceous - Tertiary theory: mantle plume and methane hydrates
Mantle plume
- Deccan traps, Indian LIP
- See P/T notes
Methane hydrates
- see P/T notes
The Anthropocene
Modern epoch defined by human activities causing permanent geological changes
Science suggests 1950 as a starting point:
- chicken bones
-new farming methods - ploughed soil with Nitrogen and phosphorus
-increased soil erosion - radionuclides
-product of nuclear fission - microplastics
-found in organisms - soot layer
-coal changes white flostone
golden spikes mark the start of the Anthropocene
Snowball earth
Occurred 647Ma
Caused oxygen in the atmosphere:
-before - 1% (too low for
complex organisms)
-after - 21% (large multicellular
organisms evolved)
Dropstones in Death Valley, California - evidence of glaciation on the equator
Formation of snowball earth
Carbon Dioxide
- supercontinent on the equator
- high weathering
- carbonates formed in seas
- trapped by cyanobacteria to form stromatolites
- locked up carbon so less in atmosphere
- temperature drops
Albedo effect
- positive feedback loop
- sea ice reflects 85%
- water reflects <10%
- tipping point at 30° latitude
