mass extinctions

What was the first pulse of the End-Ordivician extinction and what was its effects?

445mya, Cooling cause major glaciation and sea level regression, meaning warmer-adapted species and species in epicontinental seas went extinct.

What caused the first pulse of the End-Ordivician extinction, and why do scientists think so?

Sudden change in greenhouse effect - one of only explanations that match the short time period, probably caused by non-vascular plants (like moss) by accelerating weathering and decreasing atmospheric CO2, a greenhouse gas.

Other possible causes for the weathering include moving of Gondwana and Oregonies, other continents, and elevated basalt eruption rates

How do plants cause weathering?

All plants draw nutrients like Ca and Mg through rocks, causing weathering. This was previously overlooked since non-vascular plants don’t have roots, but a new study in 2012 has proved otherwise.

What Ocean Anoxication events contributed to the End-Ordovician extinction?

Extensive deep-sea pyritization. Euxinia would have been widespread to produce enough pyrite to shift the S32 ratio.

How does weathering lead to the extinction of species?

Eutrophication + deep water anoxia and euxinia leads to extinction of deep-water benthic fauna (toxic anoxic conditions) and planktonic fauna (more chemocline = less habitat)

Why is it thought that anoxia was not an issue in the 1st pulse of the End-Ordivician extinction?

No global (only local) prescence of black shales, which are indicitive of anoxic conditions, however, this was present during the 2nd pulse.

What is the most data-supported cause for the first pulse of the End-Ordivician extinction?

Since anoxia is unlikely, it was probably cooling lowering the metabolism of aerobes leading to more anaerobic bacteria. Since they favor 32S, this could account for the excursion of 34S.

What is the widespread distribution of anoxia and black shale during the 2nd pulse of the End-Ordivician extinction called?

Hirnantian ocean anoxic event (HOAE), caused by increased nutrient supply enhancing algae blooms that depleted O2 in seawater

What caused ocean anoxia in the 2nd pulse of the End-Ordivician mass extinction?

Thriving cyanobacterial mats and blooms thrived after the 1st pulse due to the extinction of grazers and competitors, leading to denitrification (not a problem for cyanobacteria, but is a problem for eukaryotic algae). More upwelling from freshwater mixing from melting glaciers caused a nutrient flux, further supporting the cyanobacteria.

In summary, the first pulse of the ordivician mass extinction was caused by

Gondwana moving over south pole, basalt eruptions, rainfall over continents in ITCA, taconic orogeny, non-vascular plants leading to glacial and sea level drops, and enhanced weathering and drop of CO2

In summary, the second pulse of the ordivician mass extinction was caused by

increase in cyanobacteria → anoxia/eucinia, non-vascular plants exhaust nutrient supply, increasing CO2 and causing warming

Which groups were most effected by the End-Ordivician mass extinction?

graptolites, trilobites (agnostids went extinct) brachiopods and bryozoans. A third of all brachiopods and bryozoans went extinct.

When did the devonian mass extinctions occur?

360mya, with 2 pulsed caused by cooling events

What indicates the devonian cooling events?

Positive O and C isotope excursions

Groups effected by 1st pulse of devonian mass extinction?

Reef builders, ammonoids, brachiopods, placoderms, coral strome reefs. Cold water inhabitants weren’t heavily affected (eg. cold adapted silica sponges)

Groups effected by 2nd pulse of devonian extinctions

placoderms completely extinct, planktonic acritarchs (microfossils) also sufferred

Causes of late devonian mass extinctions

Oceanic bottom waters became anoxic, causing benthic organisms like tropical reef communities to die. Frequent sea level changes (eg. sea level rise) also led to anoxia. Each rise was followed by glaciation and sea level fall

What exactly caused ocean anoxia in the late devonian mass extinctions?

Vascular plants on land (esp w the ones in roots). These roots broke bedrock and formed deep layers of soil. Since soil promotes weathering, nutrients were transported into the ocean causing eutrophication and anoxia (connection to ordovician!)

What caused cooling in the late devonian mass extinctions?

Large forests → reduced CO2 + weathering → cooling! This icehouse continued through the carboniferous and permian.

WHat are some potential extraterrestrial causes of the late devonian mass extinctions?

UV damage (as seen in fossil pollen and spores) → destruction of ozone because of a nearby supernova → affects surface living organisms but contradicts the cooling

How did volcanic activity cause the late devonian extinctions

SO2 ejected into atmosphere → high albedo → global cooling

Summary of late devonian extinction causes

roots and seeds → large forests → enhanced weathering → ocean eutrophication/anoxia → mass extinctions and cooling → more extinctions

potential causes: uv damage, volcanism

Effect of late devonian mass extinction on ecology

Devastating because they effected both top and base of food chain

The End-Permian extinction wiped out how many?

60% of all genera and 80% of all species, if not counted with End-Guadalopian extinction.

Consequences of guadalupian extinction?

Decline of reef-building sponges and rugose corals → reef carbonate productivity decreased by 90%, started to recover but then decimated again in P-T extinction

Fusulinids almost went extinct, with only smalled, simpler forams surviving.

How did the extinction of carbonate producing organisms effect Earth during the guadalupian event?

Bioprecipitated to chemically precipitated → increased ocean alkalinity

What other groups were effected by the guadalupian event?

Bivalves, corals (mostly marine life)

Cause of guadalupian event?

Volcanism → Emeishan flood basalts in China → ocean anoxia and acidification bc methane

End permian extinction impacted..

Marine life (extinct): Fusulinds, rugose/tabulate corals, trilobites, conodonts

Marine life (devlined): Forams, nautiloids/ammonoids, brachiopods, crinoids, echinoids, bryozoans

Terrestrial life impacts: Conifers, gymnosperms died out replaced by small lycopods. Insects and therapsids hit hard.

What caused the permian exction?

Temperature gradients decreased w/ global warming, making oceans stagnant and anoxic (evidenceL red to gray marine sediments at end of guadalupian, grey to black by end of permian)

Ocean acidification → carbonate precipitating organisms constructed smaller shells with more organic material to cope with acidification

Formation of Pangea → Ocean circulation and regression, eliminating shallow epicontental seas, leading to more stagnation and anoxia.

SIBERIAN TRAPS VOLCANISM → Sharp increase in CO2, damaged ozone layer and increased UV radiation

Effects of Triassic-Jurassic event

Conodonts and placodonts went extinct, reef building corals/sponges nearly dissapeared, almost half of all vertebrates went extinct, amphibians and therapsids hit hard, dinosaurs thrived afterwards

Cause of Triassic Jurassic extinction

Magmatic activity as pangea became seperating → normal faults formed allowing magma to rise up forming dikes, sills and flood basalts, rivalved siberian traps! → released a lot of CO2

Evidence: Stomates (cells in plants that take of CO2) in fossils, concentration decreased

This caused increase in temperature, sudden warming

Anoxia → plankton

Land plants and animals died

Why weren’t dinosaurs hit very hard during the Triassic-Jurassic extinction?

Diversity, environmental versatility, feathers/feather like coats → could flee to higher latitudes

Protomammals survive because they could burrow to escape the heat.

Crocodiles could get into water

Thus, animals that couldn’t get into water and were stuck at lower latitudes died!

WHen was the K-Pt extinctions?

66 mya

Evidence for asteroid impact

WOrldwide correlation of iridium and Chicxulub crater, indicating an asteroid 6mi wide

How did the asteroid impact kill the dinosaurs?

1. The broil → Incinerated and impacted rock leading to widepsread wildfires and tsunami accross Americas → intense heating (reentry of ejecta), rose Earth’s surface to broiling temperatures

2. Impact winter → blocked sunlight due to ash and dust → limited photosynthesis, killing base of food chain → ammonoids went extinct, plsiosaur and mosasaur went extinct → dinosaurs and land plants, lasted several months to years

3. Toxic gases and Aerosols → chemical toxicity, global cooling, rising carbon dioxide = hotter earth over < 1 million years

4. Global warming → hit very Carbon rich rocks, releasing enormous amount of CO2 → remained in atmosphere long after impact winter settled → greenhouse impact

5. Acid rain → also hit sulfur rocks = carbonic and sulfuric acid rain → sinkholes around crater due to dissolution

6. Ocean acidification → dissolving CaCO2 shells!

How did life diversify after the K-Pg extinction?

Mammals and avian birds on land, sharks and coral reefs (replaced rudist/mollusk reefs)

K-Pg debate?

There could have been a role of volcanism

Why did nautiloids survive the K-pg extinction while ammonites did not?

More generalist, protected eggs, more protection in deep sea from ocean acidification