Mass extinctions Flashcards Preview

ENVR 202 pt. 2 > Mass extinctions > Flashcards

Flashcards in Mass extinctions Deck (20):

Background rate of extinction

average number of FAMILIES (easier to tell apart) going extinct, figure it out by examining the fossil record (limits in the fossil record)



single species changing morphologically, genetically, or ecologically over a long time scale- identify them as a separate species



when a species is presumed extinct but has actually just become a different species


Rates of extinction

historically, 0.1/ million/ year


Biotic mechanisms of extinction

competitive exclusion by a closely related species, prey species develops unbeatable defense, new predator, disease


evolutionary causes for extinction vulnerability

poor disperser, at or near the top of the food chain, small range, rare, low genetic variability, specialized requirements, large body size


abiotic mechanisms of extinction

niche/habitat no longer supports species, climate fluctuations, sea level change, meteorites, volcanism


Mass extinction

extinction of a large number of unrelated species over a short period of geological time- global distribution


similarities of background and mass extinction

can both have multiple causes, both change evolutionary history


difference of background and mass extinction

different outcomes, mass extinctions= whole communities removed, previously minor species become dominant- fundamental changes


1. End Ordovician mass extinction

49% animal genera lost- marine organisms suffered most, caused by: volcanic activity depositing silicate materials- CO2 in air deposited in sea, less CO2 in atmosphere and less greenhouse effect- colder, & land moves to the south pole- glacier formation- less water in oceans


2. Late Devonian

20% of families, 70-80% of animal species lost, shallow water species impacted- dominant reef builders lost, unusually long, no single cause, combination of silicate weathering cooling globe and phosphorus erosion


Devonian plant hypothesis

large number of plants led to global cooling and lack of oxygen in oceans, CO2 in atmosphere combines with water to form carbonic acid- falls as acid rain and weathers silicates- bicarbonate erodes and ends up in ocean- CO2 in atmosphere sequestered as limestone in ocean- sped up by plants- break apart rocks and also secrete own acids


Formation of dead zones

chemical weathering of rocks by plants releases phosphorus- erodes to ocean, leads to algal blooms- algae dies and drifts down- bacteria uses oxygen to break down algae- low oxygen levels in that area


3. End Permian

"the great dying"- 70% terrestrial vertebrates 96% marine species lost- all life today descendants of the few survivors here; causes- series of massive volcanic eruptions- release CO2, methane, SO2 and burned coal deposits- global warming; lost half of oxygen content; ocean salinity increased- deep water circulation more difficult; buildup of dead matter and dead zones


4. End Triassic

76% species extinct- left empty niches on land led to rapid diversification of dinosaurs; no clear cause: gradual climate change; more minor asteroid impact; massive volcanic eruption


5. End Cretaceous

75% plant and animals species extinct- only smaller tetrapods survived, end of dinosaurs, followed by rise of mammals - rapid adaptive radiation; causes: impact hypothesis massive bolide impact, threw cloud of particles into atmosphere- global winter- interfered with photosynthesis by blocking sunlight; proof of impact in crater and iridium sediment buildup in rock layers; Deccan Traps (india)- massive basalt floods produced similar effect as previously with volcanic activity; both contributed


Press-pulse hypothesis

first even stresses environment, second even then occurs and causes a greater-than-expected impact


Sixth Mass Extinction

human impact, high rate of extinction- fast


Planned extinction

directed human efforts to drive species to extinction- "pest" species