The Great Dying Flashcards
How many mass extinctions where there in the Phanerozoic
5
What is the biggest mass extinction and why
Was at the end of the Permain, marking the end of the Palaeozoic and the start of the Mesozoic - marks the end of old life
90-95% of marine species died out
What is important about mass extinctions
Extinction is not just biodiversity loss, is it also loss in species abundance too
What were the Continents and Climate like during the Permian (~250Ma)
There was the huge Supercontinent Pangea
Which had a hige arid and tropical belt
What was Terrestrial life like in the late Permian?
- High Diversity of terrestrial animals: insects, amphibians, reptiles, mammal-like reptiles etc
- High diversity of land plants arranged in charactertic latitudinal belts
What was Marine life like in the late Permian
- High diversity of Crachiopods, Gastropods, corals, ammonoids, trilobites, echinoderms, bony fish and sharks
- Characteristic shelly faunas found in different environments - shallow/deep, near/fareshore, lagoon, reef
What affect did the Late Permian extinction have on Marine Organisms
Groups which survived, where highly compromised
Some species like Bivalves and Gastropods and increased in numbers again later on
What are the issues with the Triassic Palaeo records
Sedimentary rocks are poor in fossils from the Permian era
Every marine creature and almost every tetrapod belonged to an abundant cosmopolitan species - not affected by temperature change and can live across many latitudes
What is the suggested reason for the late Permian extinction
- Most agree global warming was underlying cause, though kill mechanisms are controversial
- Plant fossils suggest a temperature rise of 6 degrees at the equator
- Geography of flora and fauna siggest temp rise was higher at higher latitudes
What is the suggested reason for the global warming which caused the mass extinction
- Pole-to-equaotr temperature gradient drives circulation of oceans
- If there isn’t a signifcant enough gradient, circulation could slow and possibly stop
- Oxygen isn’t been transported into deep water, killing marine organisms which would settle on the sea floor, further using up oxygen to decay
- Causing anoxia of the water column which few creates would survive
What is the modern analogue for halting of Ocean circulation
Black Sea anoxia
The black sea is supplied by the ocean and freshwater from rivers - hence not as salty as open sea
The top layers are oxygenated which are churned due to wind - meaning fish can only live in the surface
The bottom however is anoxic
There was an anoxic sea event 93Mya, how did it occur
- Caribbean eruption, put micronutrients into sea water
- This caused increased plankton bloom
- These plankton would then died and be decayed using up oxygen in water - causing anoxia
What is another suggestion for the warming, related to the Siberian Traps
- Part oxidation of uplifted coals, near the south pole, put CO₂ back into the atmosphere
- Release of CO₂ and other greenhouse gases by eruption of Siberian Traps
- However chemical analysis of rock from molten shows negative 13C excursion, which cannot be explain by Siberian traps
How could Clathrates explain the Global warming, which caused the Late Permian extinction
- Clathrates are found on the sea floor, and they exist as part of the decay process producing methane
- This methane is changed to Quasi-solid material as methane clathrates
- It stays in the oceans in cold, high pressures
- If you have global warming, the Clathrates will bubble up into the atmosphere which will warm the planet
- This idea is consistent with isotopic evidence which argures for a biological source 12C
Why was this warming by Clatherates so disasterous - we have had warming before
The geography of the Permain is the reason
Pangea, meant low diversity and species where not as adaptable to a chaning climate
Shallow contiental shelves following the circumference of pangea, means that organisms could move completely around the Earth
