lecture 5 - extinction Flashcards
(14 cards)
What is extinction?
The complete disappearance of a species or higher taxon, leaving no living representatives anywhere.
What percentage of all species that ever lived are now extinct?
Over 99.9% (estimates suggest 5–50 billion species have existed; only ~50 million exist today).
Contrast background and mass extinction.
Background: Steady rate (~2–4.6 families per million years).
Mass: Rare, catastrophic events wiping out >50% of species (e.g., Permian-Triassic).
List the “Big Five” mass extinctions.
End-Ordovician (445 Ma)
Late Devonian (360 Ma)
End-Permian (252 Ma; “Great Dying”)
End-Triassic (201 Ma)
Cretaceous-Paleogene (K-T) (66 Ma; dinosaurs).
Why was the End-Permian extinction unique?
96% marine species, 80% genera, 75% land vertebrates died.
Causes: Siberian Traps (massive volcanism), ocean anoxia, CO₂ release.
Aftermath: “Lilliput Effect” (dwarfed fauna), 10M-year recovery.
What evidence supports the asteroid impact hypothesis for the K-T extinction?
Iridium layer (meteoritic element).
Chicxulub crater (180 km, Yucatán).
Shocked quartz, tektites, fern spike (rapid colonization post-disaster).
Explain the Red Queen Hypothesis.
Species must constantly evolve to survive amid competing organisms and changing environments (“run to stay in place”).
Extinction risk remains constant over time.
What do survivorship curves reveal about extinction?
Old species are no better at surviving than young ones.
Extinction is largely random (“bad luck” vs. “bad genes”).
What groups were hit hardest in the Late Devonian extinction?
Marine life: Reef-builders (stromatoporoids, tabulate corals), armored fish (placoderms), trilobites.
Cause: Global cooling, ocean anoxia, possible impacts.
What triggered the Late Ordovician extinction?
Glaciation (Gondwana over South Pole) → sea-level drop.
Marine impact: Warm-adapted species (e.g., brachiopods, graptolites) most affected.
Key features of the End-Triassic extinction.
48% marine genera lost (ammonites, conodonts).
Causes: Volcanism (CAMP), ocean overturning, Manicouagan impact crater.
What caused Pleistocene megafauna extinctions?
Human hunting (e.g., Folsom points in Americas).
Climate change (last glacial-interglacial transition).
Do all mass extinctions share a single cause?
No—proposed triggers include:
Volcanism (Siberian/Deccan Traps).
Impacts (Chicxulub).
Climate shifts (cooling/warming).
Ocean anoxia/regression.
Is there a 26-million-year extinction cycle?
Unlikely—patterns may reflect recovery times rather than periodicity.
