L8 - Extinction and Global Change Flashcards
Background to extinction?
Extinctions occur continually, generating a turnover of the species living on earth. This normal process is called background extinction. Sometimes, however, extinction rates rise suddenly for a relatively short time - an event known as mass extinction. Mass extinctions kill off many species, but the empty niches left behind may allow other lineages to radiate into new roles, shaping the diversification of life on earth.
What are the 5 mass extinction events in our planet’s history?
Cretaceous-tertiary
End triassic
Permian triassic
Late devonian
Ordovician-silurian
What happened in the Ordovician-Silurian extinction (440 mya)?
26% of marine families, 60% of all genera, an estimated 82-88% of all species extinct. Although no major groups were completely lost, many sea creatures suffered substantial losses. At the end of the Ordovician period, the world entered an intense ice age, possibly brough about by the location of the supercontinent Gondwana over the southern pole.
What happened in the Late Devonian extinction (364 mya)?
22% of marine families, 57% of all genera, an estimated 79-87% of all species went extinct. Armoured fish (ostracoderms and placoderms) vanished completely. Plants and insects suffered remarkably few extinctions but there was a significant impact on most marine groups. The causes of this drawn-out mass extinction are far from certain, but it was a time of major environmental change. The first phase has been linked to a lack of oxygen in the ocean (anoxia), combined with rising sea levels and global cooling.
What happened in the Permiam Triassic extinction (250 mya)?
51% of all marine families, 82% of all genera, an estimated 93-97% of all species. Having survived 2 mass extinctions, only a few localised and specialised populations of trilobites remained. A single supercontinent, Pangaea, stretched from pole to pole in the permian period. This huge landmass created extremely hot, dry conditions across most of the interior. By the later permian, global temperatures were the highest they’d ever been.
What happened in the End Triassic extinction (200 mya)?
22% of marine families, 53% of all genera, an estimated 76-84% of all species. Most mammal-like reptiles and large amphibians disappeared, as well as many dinosaur groups. This extinction is probably the least understood of the big five, because of the lack of accessible sediments for scientist to study. Most of the evidence suggest falling sea levels were probably responsible for the longer-term extinction patterns.
What happened in the Cretaceous - tertiary extinction (65 mya)?
16% of all marine families, 47% of all genera, and estimated 71-81% of all species. The most famous victims were the non-avian dinosaurs. The end-cretaceous mass extinction is famously associated with a large asteroid impact. While plenty of evidence shows at least one huge asteroid or comet slammed into earth at this time, whether it caused or simply contributed to the extinctions is stilly hotly debated. Many palaeontologists think that the story is more complex.
The current (sixth) mass extinction?
The global living planet index (1970 to 2018). 69% decrease in pop abundance. Nearctic showed 23% pop decline (1970 to 2014). Neotropical showed 4.8% pop decline annualy. Afrotropical 56% decline (1970 to 2014). Indo-pacific showed 64% decline. Freshwater pops declined by 83%. Red list index
What are the anthropogenic drivers of current extinction?
Human effects - Climate change, temperature, extreme events, sea levels, habitat destruction,
