Test 2 191 Mass Extinctions

End Permian—Context for Triassic

10 degrees warming

-1 pH, Ocean acidification

100x increase in anoxic, loss of 80% of ocean Co2

Early Triassic characterization

gradual recovery of diversity after the End-Permian extinction, slow recovery of biotic systems

Earliest triassic on land

Lystosaurus was widespread across Pangea

ancestor of mammals, one of the only surviving vertebrates, 95% of individuals on land

may have been able to go into hibernation, may have been herbivores

Earliest triassic in ocean

coral reefs replaced by microbial carbonate mounds for up to 6 million years, barely anything in first millions (loss of microalgae, metazoan, deposit feeders and mobile predators)

Early Triassic in oceans

No marine mammals

Nothosaurus (not a dinosaur) a reptile that could use legs

Plesiosaurs fully aquatic marine predator (went extinct at K-Pg)

Triassic on Land

Dinosaurs ruled, mammals scurried around at night

Triassic Extinction Severity

Similar extinction numbers to K-Pg

Factors causing End Triassic extinction

Pangea break up and Central Atlantic Magmatic Province (CAMP)

Pangea Breakup Triassic Extinction

rifting between N. America and Africa causes lava to pour out and cover lots of land, creating mountain ranges. This is why Applachians look the same as mtns in Tunisia

CAMP

Central Atlantic Magmatic Province (end Triassic)

2 large pulses over 300k year

2nd most intense volcanic province event after Siberian Traps (order-deccan, camp, siberian)

T-J Victims Underwater

100% extinction of Conodonts

Sever effects on corals, brachiopods, sponges, ammonites

Relatively unaffected: fishes, marine reptiles, gastropods

T-J selectivity on land

100% extinction of phytosaurs (crocodile relative)

Severely reduced: amphibians (which were huge)

Unaffected: basically everything else… plants, insects, mammals… dinosaurs diversified after extinction maybe because taking over other ecosystem roles

Archosauromorphs

Phytosaurs (crocodile relatives that went extinct in tj), crocodiles, turtles, dinosaurs, pterosaurs

All more closely related to each other than snakes or lizards

Ecosystems/Traits hit hardest by T-J extinction

Reefs, Ectotherms (coldblooded animals), stationary bivalves, plants with big leaves

Kill mechanisms anfd ecosystem effects of T-J

Ocean acidification (reef systems highly affected)

Warming (explains impact on big leaf plants)

Cooling (consistent with ectotherms doing poorly, could have happened periodically because of volcanic activity

Kill Mechanism because of CAMP LIP

GGs: Ocean acidification, anoxia, warming, cooling. release of halogen gases leads to ozone destruction which leads to terrestrial mass extinction

Evidence for High CO2 and warming in T-J

stomata density decrease indicates high Co2 (bc they take in the carbon dioxide)

small leaf plant survival indicates warming because could conserve more water

Evidence for Anoxia T-J

Uranium isotope, black shale, fossils from bacteria that use hydrogen sulfide to photosynthesize instead of oxygen

Other kill mechanisms for T-J

Ozone depletion, mercury poisoning released from volcanism, wildfires

Diversity recovery post T-J

First ocean - ammonites, plesiosaurs, Icthyosaurs, then reefs built by rudist clams

By the cretaceous, we had phytoplankton like cocolithophores, giant fully marine turtles

Late Mesozoic/Cretaceous Planet

Pangea is broken up but continents still not in modern placements, no polar ice caps

Super high temps, rainforests near poles and seal level so high there are seaways across continents

Life on Land in late Mesozoic.Cretacious

Dominated by dinos but mammals, reptiles, birds also flourished

Evolution of flowering plants! but no grasses

Ginkos widespread and nowadays used for atmospheric Co2 reconstruction

Life in Ocean in Late Mesozoic/Cretaceous

Large marine reptiles: plesiosaurs, mosasaurs, aquatic dinos

Large predatory fish and sharks

ammonites dominated

evolution of large celled plankton groups like diatoms and cocolithophores

What went completely extinct in the K-Pg?

100% loss of all non-avian dinosaurs and large marine reptiles

Ammonites

Tetrapods over 25 kg (but not turtles)

What species were severely impacted in the K-Pg?

Calcareous plankton, reef building corals

Important K-Pg survivors on land

Small mammals, avian dinosaurs, flowering plants, burrowing species/species that hibernate, ants and butterflies, amphibians

K-Pg Survivors in the Ocean

Squids/octopi, small deep sea fish and sharks, deep water corals, turtles and crocodiles, diatoms and dinoflagellates

K-Pg Kill Mechanisms and patterns that show them

Ocean acidifcation- shallow water ecosystems did poorly

Fires, loss of sunlight — burrowing animals survived

cold - warm blooded animals survived

loss of food (plants)- detritivores survived well

Deccan Traps LIP

Volcanism over 1 million yrs in India, long suspected as cause of the K-Pg, now we know it isn’t the main reason

Caused brief cooling but overall warming in late cretaceous.

Mass extinction and LIP relationship

Many mass extinctions are associated with LIPs or but LIPs are not associated with mass extinctions

Discovery of mysterious clay layer - uncovering K-Pg

Mysterious global clay layer Alvarez father and son decide to measure elemental levels in the clay layer

Iridium layers 1000x higher than background layers and only known source of high iridium is asteroids

Evidence for asteroid impact

• Chixulub crater

• Geologic tsunami deposits

• Iridium isotope enrichment

• Tektites and impact spherules

• Widespread forest fires

• Shocked Quartz

What is the Strangelove Ocean Hypothesis?

The hypothesis is that there was a nuclear type winter after the asteroid hit because of particulates/ash/smoke/debris filling the atmosphere. The evidence was a carbon isotope change in the ocean. In the normal ocean, plankton at the surface use doing photosynthesis use C12 more because it is preferred as the lighter isotope, leaving more C13 in the ocean. However, with the debris and dust in the atmosphere blocking out the sun, photosynthesis wasn’t happening, so way more C12 in the shallow ocean at this time

Name comes because of analogous nuclear winter scenario from a movie about atomic bomb

coccolithophores extinction

When did scientific ocean drilling begin and what is its significance?

It began in the 1960s, led to the field of paleoceanography looking at ancient oceans, sediment cores shows with microfossils show huge drop in diversity

What do deep sea records show?

Instantaneous extinction

loss of diversity in microfossils

Signor-Lipps Effect

It appeared that the dinosaurs were declining in the last 10 Myrs before K-Pg but that was actually this effect which happens with bigger species, because they are less abundant in microfossils they appear like they are declining but actually undersampled

Were the Deccan Traps the cause?

No, the impacts of the Deccan traps were observed before and after the asteroid impact without causing significant biological or ecological changes

Finding the crater

Early 1990s, gravity anomaly hinted at location of crater, scientific ocean drilling in 2016 confirmed age

Effects of Darkness post asteroid

Impact ejecta clouded the atmosphere and was eventually rained out as sulfuric acid

Photosynthesis stopped 6-24 month

When did the asteroid hit?

Northern Hemisphere spring, as a result, S hemisphere taxa did better, possibly because they were already winding down for winter

What happened with life post-impact

Even at spot of impact, microbial life returned within hours/days. Eventually multicellular life as well. Surviving species dominated the post extinction environment

Beginning of the Cenozoic (post K-Pg)

Major increases in animal diversity, general increase in diversity, large radiation of rayfin fishes

Overall diversity curve

The K-Pg was just a blip in a fast rising diversity curve, not a real diversity setback

How long ago was the K-Pg? Summary?

66 million years ago. Wiped out about 70% of life and restructured ecosystems, change from Age of Dinosaurs to Age of Mammals

2 most affected groups in K-Pg

Large bodied organisms and surface dwelling calcifying organisms

Most successful organisms post K-Pg

small-bodied, burrowing, and deep water organisms survived and radiated after

Paleocene-Eocene Thermal Maximum (PETM)

Extremely warm time on earth, warmed fast—5 degrees C in only 15-20,000 yrs, time of the land bridges

Beringia land bridge

From Asia to N. America, you could walk across in the Eocene across the North Pole

Evidence of the PETM

Fossils of Palm trees in Antarctica, geology indicates high sea levels, huge lakes in Western US, isotope signatures

Reasons earth was hot during the PETMS

High amounts greenhouse gasses over a period thousands of years. Possible sources include widespread wildfires, lava intrusions on coal seams in Greenland and Norway, release of methane hydrate from ocean floor or melted permafrost

Effects of PETM on ecosystems

Warm climate allow animals to travel across land bridges to other continents. Primates/other mammal groups travel to N. Am for the first time. Many from Eurasia traveled to N. America, evolved more, and later traveled back

PETM and Ocean acidification

High CO2 lead to acidification, causing extinctions. Equatorial waters may have been too hot to survive in. Acidification causes shells to dissolve (which are hard to grow)

What comes after the Eocene/PETM?

Global Cooling, oligocene starts with ice caps in Antarctica

What caused Global Cooling? Reason 1

Antarctic Circumpolar Current (ACC) formation. Antarctica separates from S. America and new ocean currents formed. The ocean surrounds Antarctica, isolating it and creating a self refrigeration process because its the world strongest current, and the ice albedo feedback keeps it cool. The current is 1000x bigger than the Amazon river

What caused global cooling? Reason 2

Greenland Scotland Ridge (GSR) Ocean barrier

Under the ocean in Iceland, a geothermal hotspot strengthened and weakened, causing a ridge to rise which cut off the Arctic from the Atlantic, leading to quicker flow of water to the south pole, thus cooling it. Then later the ridge dropped and water could circulate up to the arctic, then cooling it there

What caused global cooling? Reason 3

Uplift of the Tibetan/Himalayan Plateau: mountain uprising leads to erosion which ultimately acts to take carbon out of atmosphere and deposit it in the ocean

What are azolla ferns and could they have ended the PETM?

hypothesized to have been present in huge mats covering ocean and sucked up to 80% of the co2 out of the atmosphere. They grow in freshwater but in the Miocene the arctic may have been a black sea with fresh on top of salt water

How does azolla then differ from tree planting now?

The Azolla mats cooled the earth by sucking up co2 and then sinking to the bottom and becoming fossil fuels, and as such the carbon could not be recycled back into the atmosphere. Trees today are not a carbon sink, they photosynthesize and respire. Trees also contribute co2 by dropping leaves, burning in fires

Overall cooling trend post PETM, then ice age cycles?

After Initial cooling post PETM, never got significantly warm like that again, and then 2.4 million years ago earth entered the ice age cycles

Ecosystem changes during the oligocene and miocene (times of ice ages)

Emergence of widespread grassland

Emergence of kelp forests

Major animals during ice ages in CA

Columbian Mammoth, American Mastodon (elephant relatives)

Mountain lion, american lion

California condor, merriams’s giant condor, Brea condor

2 hypotheses for ice-age extinctions

Overkill hypotheses: no proof that this is what happened but more recent history proves it is possible

Climate change: S. American megafauna also went extinct without hunting

California Survivors of Ice Ages

California Condor and Cougars/mountain lions

What was the average length of Pleistocene ice-age cycles (the length from one glacial interval to the next)?

100,000 years

3 kinds of Earth’s wobble

Tilt/Obliquity, Precession (wobble), Eccentricity (shape of orbit)

Factor that is the biggest determinant of Glaciation

strength/length of S. hemisphere winter

If the earth has always wobbled, why haven’t we always had ice ages?

Because orbital forcing is influenced by factors such as atmosphere composition, ocean circulation, ice, continent arrangement