End Permian and Cretaceous Extinctions Flashcards
When was the end Permian extinction event roughly?
250mya
What was the state of Pangea at the start of the end Permian extinction?
Still largely together
What are the two possible causes for the end Permian extinction and which is mostly recognised?
Extra-terrestrial (mostly ignored) and vulcanism (mostly accepted)
What evidence is there for an end Permian extinction being caused by extra-terrestrial impact?
Discovery of a crater in Australia that contained:
quartz structures
fullerenes with argon and helium isotopes that suggested extra-terrestrial source.
What were the two problems with the evidence for the end Permian extinction event being caused by an extra-terrestrial impact?
No iridium present (key)
Fullerene results were not reproducible
What are the two ways that vulcanism could have caused the end Permian extinction?
Ozone layer alterations
GHG and temperature increase
Explain how the ozone layer alterations caused by vulcanism could have caused the end Permian extinction?
The release of gases and volatiles in to the atmosphere from the volcanic source could have altered the ozone layer and allowed more UV light to penetrate the terrestrial sphere leading to mutagenesis for plants
What was the source of the volcanic activity that caused the end Permian extinction?
Siberian Traps
What area did the Siberian traps lava flows cover, what volume were the flows, how deep were they and how many years did they erupt over?
Area covered: 1.6mn km^2
Volume: 2mn km^2
Depth: 3km
Duration of eruption: 1 million years (tens of thousands of years?)
How would the Siberian traps have increased atmospheric GHG concentration?
As the lava flows from deep rise up through the crust they cooked the organic 12C-rich sediment layers which were then released in to the atmosphere
By how many degrees Celsius did the temperature of the atmosphere rise by following the release of organic carbon by rising lava flows?
10 Degrees Celsius
What evidence is there for how the vulcanism cooked the organic carbon sedimentary layers?
Because the biosphere mostly prefers 12C, this is what was mostly stored in the sedimentary layers. When the lava flows cooked this layer rich in 12C it was all released to the atmosphere where it was then once again consumed rapidly by plants that prefer the 12C which had become re-available for use in photosynthesis. This meant when the biosphere from the period of the Siberian traps eruptions decomposed, there was another layer of organic carbon rich in 12C.
How did the high GHG (CO2 concentration) affect oceans and then cause the end Permian extinction event within the oceans?
The high CO2 concentration would have meant that a lot would have dissolved in to the oceans which would have acidified it to a large degree. This is bad for calcifying organisms such as organisms that produce carbonate/foraminifera shells that were found to have declined in production
What happened just before the oceans in the end Permian extinction event acidified?
They became increasingly anoxic
What evidence was there of the oceans becoming more anoxic just before the end Permian extinction event?
Disappearance of larger and more complex organisms from the record and rise of hydrogen sulphide, which only happens when oxygen declines
What are the two causes for the ocean becoming increasingly anoxic just before the end Permian extinction event?
- Vulcanism
2. Temperature
How does vulcanism cause the ocean to become increasingly anoxic just before the end Permian extinction event?
Vulcanism produces lava flows, rich in phosphorus, that get washed to oceans because of solubility, it fuels marine biosphere productivity of oxygen in a short burst, oxygen consumed by organisms at great depths but no more eruptions means that there is no more oxygen produced but because the organisms are now hungry for oxygen it continues to be consumed but not replenished
How does increased temperature lead to anoxia at the end Permian extinction?
Increased temperature means CO2 dissolves less in oceans, this means less supply of sole oxygen element to oceans because it is not being split from a carbon molecule and so the ocean becomes anoxic in nature
What was the impact of the end Permian extinction event upon marine, continental and total biodiversity?
Marine loss: 49%
Continental loss: 63%
total: 61%
What impact did the end Permian extinction even have upon flora and geology?
forests were eradicated and replaced by fern types which meant erosion rates increased
What was the only animal left after the end Permian extinction?
lystrosaurus
How long did it take for ecosystems and biodiversity to recover after the end Permian extinction?
Ecosystems: 10myr
Biodiversity 100myr
What fauna emerged after the end Permian extinction?
Dinosaurs and gymnosperm plants. More mobile to non-mobile fauna and more predators to prey
When was the end cretaceous extinction event?
66mya
What is another name for the end cretaceous extinction?
K/T or KPG
What was the state of Pangea like at the end cretaceous extinction?
Close to today levels
What are the two primary causes for the end Permian extinction event?
Extra-terrestrial impact
Vulcanism
What evidence is there for the end cretaceous extinction event being caused by an extra-terrestrial impact?
Alvarez & Alvarez (1980) found a strong iridium content in the geology which later Hildebrand supported by finding a crater in the same place.
Explain how the vulcanism caused the end cretaceous extinction event?
Eruption of large igneous province led to release of GHG and the consequent increase in the atmosphere.
What was the source of the vulcanism that caused the end cretaceous extinction event? What volume were the lava flows and what duration did they erupt over?
Deccan Traps had a volume 365,000km^2 and erupted over 800kya
What was the secondary cause for the end cretaceous extinction?
Reducing photosynthesis activity and shutting off of the biological pump
What were the two proposed causes for the reduced photosynthesis activity?
- Anoxia of the oceans (Vulcanic activity and temperature)
2. Debris from asteroid preventing insolation
What impact did the shutting off of the photosynthesis activity have?
The shutting off of photosynthesis meant that nanoplankton species declined and so where they would have absorbed CO2 at the surface then decomposed and sunk to the ocean depths this no longer happened because they no longer existed.
What was the process by which carbon was no longer transported to the bottom of the oceans by decomposing nanoplankton?
Shutting off of the biological pump
What % of nanoplankton species died?
90%
What impact did the shutting off of the biological pump have upon climate and calcifying organisms?
No CO2 being transported to the depths meant calcifying organisms at depths would not receive carbon they needed to form carbonate shells, and because the carbon was now accumulating at the top of the surface this meant it was better able to escape to the atmosphere which it did (leading to a 2-3X increase in atmospheric CO2) adding to the GHG released by the Deccan Traps.
What impact did the end cretaceous extinction have upon fauna?
Dinosaurs extinct and only burrowing species survived such as crocodiles
What impact did the end cretaceous extinction have upon flora?
Evergreen vegetation suffered while high-altitude colder climate vegetation survived
