Lecture 20: Extinction Flashcards by Minda Wood

Whats the definition of extinction

The birth rate of an organism does not keep up with the death rate

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What is a Background extinction?

Less dramatic than mass extinctions, slower and longer. 95% of all extinctions are accounted for by BG extinctions

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What are the causes for a background extinction?

Depletion of resources in habitat, Competition for food and space, changes in climate, development of mountain ranges, habitat destruction through fire, river migration, drying of wetland, eruption of Volcanoes

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What is a mass extinction?

Large numbers of species and types of species go extinct. Effect MUST take place on a global scale, happens over a short period of geological time

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Times Of mass extinctions

Late ordovician (438ma)
Late Devonian (380 Ma)
Permian (245ma)
Late Triassic (208ma)
Cretaceous/tertiary (65ma)
Today?

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Modern extinction crisis

We are losins species 1000 to 10000 times the background rate (aka dozens every day)
99% of species are at risk from human activity

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Permian Extinction 250 Ma ago

Most severe mass extinction
96% of all species died & 52% of all families
over 2 mill years
Glaciation-sea level drop, reduced amount of shelf space
Large volcanic eruptions siberia/arctic

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Triassic Extinction 200 ma ago

two phases, flood basalts of the Central Atlantic magmatic province
loss of 76% of marine and terrestial species
20% of families
Opening of ecological niches for the dinosaurs to thrive

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Problems with extinctions

Incompleteness of fossil record, incompleteness or sedimentary record, resolution

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Effect of sampling

Biostratigraphic ranges, last appearance datums and species dissapear at different levels in different areas

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The K/T event: early studies focused on?

Dinosaurs- were they too big? too stupid? too undesexed to survive? too constipated? or too weird?

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The early theories

Suffered competition for food sources from mammals and insects
poisoned by plants
slaughtered by plagues
wiped out by shocked climatic change
By extraterrestial catastrophes

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Problems with the early theories

Other groups went extinct
some groups survived
Multitude of data: 
-environmental changes
geochemical changes
-land and sea
-decline and replacement of fossil groups

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Groups with losses or total disappearance

Land animals: dinosaurs, pterosaurs, some birds, some families of marsupial mammals
In the sea: mososaurs, plesiosaurs, some ray finned dish, amonites and belemintes, rudist clams, certain mollusks, inoceramid bivalves
Plankton, over half of various groups

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Survivors

Most land plants, insects, snails, frogs, salamanders, turtles, lizards, snakes, crocodiles, placental mammals, Marine invertebrae (starfish, sea urchin, mollusks, many fish)

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Causes of exctinction

What was the earlth like at the end of the cretaceous? Intense tectonic acitivity, formation of Rocky mountains and andes, in europe Alps and volcanisms

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Signs of Volcanism

Extensive sea floor spreading at pacific rim, development of volcanic arcs, huge basalt flows

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Deccan traps in India

Flood basalts (volcanic rock)
60-65 mya
large amounts of volatile gas
-carbon dioxide, sulfur oxide and nitric oxide
-temperature change, damage of ozone layer-acid rain

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What causes cooling?

Greenhouse is delayed
SO2 oxidizes in atmosphere to SO3
Sulphur trioxide is primary agent for acid rain
Micro droplets of sulphuric acid
Droplets are smaller than wavelength of light- Photons that meet a dropletmight be returned to space
ice formation- drop in sea level- hardgrounds and incised river valleys

Continental configuration- similar to that of todays, except for

Exceptions:
-Land bridge connected North America and Asia
Africa was isolated
South america was connected to anartica/australia by most southern tip
-india in the middle of the indian ocean

Oceans

High sea level throughout cretaceous, regression towards the end, new oceanic crusts cooled and subsided, epeiric seas dried out

What was the climate

Warm during cretaceous, Greenhouse effect, CO2 to atmosphere due to tectonics, cooling and seasonality started during 2nd half of period, drop of 5 degrees

Asteroid impact

Gubbio section in italy, 3 layers in marine sediment

Iridium Layer

Element of the platinum group, rare in earth surface material, higher concentration in earth core and METEORITES (so evidence)
much higher concentration at Gubbio. Over 100 sites are discovered with iridium anomalies

Shocked Quartz as an indicator for an impact

Quartz crystals where the crystal structure has been shattered, found in sediments marking the K/T boundary, caused my meteorites smashing into earth

Microtektites (evidence)

Are small droplets of silica rich glass, material of meteorites, thrown up into atmosphere in a molten state, becoming solid after cooling and falling back to earth

Search for the impact site

haiti: sequence of glass--> 1 M thick, rich in sulfur, resulting from molten continental crust and evaporites Yucatan peninsula: in 1991 a bowl shaped structure was found, 180 km in diameter and drilling revealed shocked quartz, sequence formed between continental crust and evaporite deposits Chixclub crater 65mil

immediate regional effects

Blast wave, base surge, Tsunamis, vaporization of water, vaporization of rock, earthquake

Short term global effects (days to weeks)

Global distribtution of ejecta and global wildfires

Long term global effects (months to years)

Global darkness, acid rain, greenhouse effect

What was the impact?

Tsunami, evidence at the gulf coast at the K/T boundary. Relased by impact? Short term global warming, release of large amounts of energy in form of heat (increase of 30 degrees for 30 days) Global wildfires (soot rich horizons found in Europe and New Z.) rich in carbon Acid rain and nitric acid rain rapid heating of atmosphere long term global cooling blockage of sunlight (lasting 3 months or longer)

Long term global warming

Most of biomass gets exterminated, Biomass decease amount of CO2, no biomass= increase in Co2 in atmosphere= greenhouse effect

Link to biological record

The clay layer is one true signal of a catastrophic impact

Iridium clay layer reflects 3 months around the world

effects on biota have to be studied in oceans atmosphere land

Paleoenvironmental change

Animals thrived in epeiric seas, these dried up due to lower sea levels, lack of easily accessible fossil record on land sections

Formanifera

Benthic, Planktic, large abundance and short biostratigraphic ranges

Primary productivity

Measured by carbon Isotopes, measured on bnthic and planktic foraminifera. Primary productivity broke down at K/T boundary

Importance of palynology

-palynoflora: spores and pollen | Megaflora; leaves etc.

Terrestial record

In Montana, North dakota and Wyoming: Pollen extinction at iridium followed by abundant ferns followed by new assemblage of flowering plants

Terrestial record in Canada:

A series of 5 major pollen changes related to different latitudes, series of extinctions related to climate changes, not only at K/T boundary

Vertebraes

Research from montana; 150,00 specimens were collected around boundary Aquatic animals survival-90% Land animals-10%

Dinosaurs

Decline of dinosaurs took place over 7 Million years before boundary but acceleration in the final 0.3 million years, competition of mammals

Problems with post extinction dino research

Study conducted on a family level, genera and species could have dropped out earlier. North america was one of the last localities for Dinosaurs

arguments for asteroid impact

1) global impact? yes 2) independent of climatic zones? yes, bivalves become extinct 3) gradual decline or shock? evidence of gradual decline of lineages in mammals argue against impact

Marine life

Marine animals depending on primary productivity became extinct but marine animals surving on detritus (remains of dead organims) survived - scavengers - suspension feeders - often benthic

Terrestial Life

Aquatic animals survived lakes adn wetlands act as sinkholes for detritus large role of primary productivity

Why were mammals survivors?

Removal or dinosaurs triggered radiation of mammals, creation of ecological oppurtunities, mammal paleontologists argue against asteroid theory