mass extinctions Flashcards
mass extinction
a massive decline in the number of different species, over a relatively short period of time, perhaps spanning several thousands or millions of years.
what was the most likely cause of cooling temps at the Ordovician- Silurian boundary?
an ice age, a huge ice sheet extended over the southern hemisphere
what would the presence of an extensive ice sheet (OS) have caused? X3
climate to become cooler, by the albedo effect
sea levels fall, as water would fall as snow and become trapped in the ice cape
changes in ocean chemistry, moving to less favourable conditions
what was the environment and biota like during the Ordovician?
most life existed in the sea
dominated by trilobites, brachiopods and graptolites
relatively warm temps lead to cooling event
what were the effects of the Ordovician Silurian mass extinction?
falling sea levels disrupted or eliminated habitats on continental shelf
caused problems for shallow benthonic organisms
planktonic and nektonic organisms seriously effected
what are the possible causes for the Permo-Triassic mass extinction?
formation of Pangea
volcanic activity- Siberian traps
methane hydrates
what were the effects of the formation of Pangea? x3
fewer continental shelves= lack of habitat for shallow marine dwellers
single continent = rapid fluctuations in climate + unstable weather patterns
parts were over north and south poles= wide spread glaciation= sea level fall= reduces habitat
traps
large scale volcanisms resulting in formation of igneous rocks
how long did the Permo-Triassic eruptions last for?
2Ma
what were the effects of volcanic activity? PT
toxic gases, lava flows and pyroclastic flows
ash blocked out sun light, lowering temps= glaciation+ sea level fall
after cooling, greenhouse gases increased temps + caused acid rain
what are methane hydrates and how were they released?
solid form of methane, formed within sediments, solid and stable up to 18c. increase in temps triggered methane hydrates in seabed to become mobile + gaseous = released.
what were the possible causes of the Cretaceous-Tertiary Mass extinction?
volcanic activity- Decan Traps
impact of asteroid or meteorite
what is the evidence for a large object hitting earth? x5
layers or iridium concentrated in clays shocked quartz grains tektites near crater large scale sedimentary evidence of a huge Tsunami large meteorite crater
describe the volcanic activity during the cretaceous -tertiary mass extinction
enormous eruptions in India, covering 500,000km^2. same effect as the Siberian traps
name the three mass extinction?
Ordovician Silurian
Permo- Triassic
Cretaceous- tertiary
