Mass Extinctions and Climate Variability

Question 1

Adaptive Radiation

Answer 1

changes in the environment that create new niches that contribute to rapid speciation + increased diversity events

Question 2

Cataclysmic Events

Answer 2

devastating losses of diversity due to extinction events
- erases some genetic lines
- creates room for other to evolve into the empty niches left behind
- the anaerobic extinction that occurred in the Great Oxygenation is NOT one of the 5 mass extinctions of the Phanerozoic

Question 3

Mass Extinctions

Answer 3

• define the geological periods of the history of life on Earth
• typically occur at the transition point between geological periods
• transition in fossils from one period to another reflects the dramatic loss of species and gradual origin of new species
• FIVE

Question 4

End- Ordovician EE

Answer 4

2nd largest recorded EE; ~85% of marine species (land plants + few animals lived outside the oceans) became extinct
- leading hypothesis: caused by a period of glaciation then warming in a rapid 1MY timespan, affecting both the climate + sea levels, and with the cooling + warming each causing a round of extinction

Question 5

End-Devonian EE

Answer 5

affected primarily marine species, not terrestrial plants and animals
- causes are poorly understood

Question 6

End-Permian EE

Answer 6

LARGEST recorded EE in the history of life, with ~96% of marine species and ~70% of terrestrial species lost

Question 7

End-Permian EE: Impact on Biodiversity

Answer 7

• The trilobites, a group that survived the end-O EE, became extinct. Many seedless land plant lineages disappeared
• the loss of some dominant species of Permian reptiles made it possible for the dinosaurs to emerge
• terrestrial tetrapod diversity took ~30 MY to recover
• the warm + stable climate conditions of the following Mesozoic promoted explosive diversification of dinosaurs into every conceivable land, air, and water niche
• First lycophytes then gymnosperms dominated, creating complex communities of producers + consumers, some of which became very large due to abundant food sources

Question 8

End-Permian EE: Causes

Answer 8

“the unexplained catastrophe”; leading suspect is extended + widespread volcanic activity that led to a runaway global warming event
- massive layers of basaltic rock in the Siberian Trap indicate extreme eruptions
- high global temps. would have resulted from the increased CO2 and methane in the air from volcanic activity
- warming water and nutrient runoff from dead and decomposing terrestrial species would have caused oceans to become largely anoxic - suffocating O2 dependent marine life

Question 9

End-Triassic Extinction

Answer 9

hypotheses of climate change, asteroid impact, and volcanic eruptions are proposed and not mutually exclusive
- occurred just before the Pangea breakup
- could have occurred gradually throughout the Triassic

Question 10

End-Cretaceous EE

Answer 10

not the biggest but the most famous because if saw the loss of all dinosaurs except a theropod clade that gave rise to birds

Question 11

End-Cretaceous EE: Death and Recovery

Answer 11

• Plants died, herbivores + carnivores starved; animals more than 25 kg became extinct as a result
• recovery times for biodiversity are shorter in geological time than in end-Permian
• plant life and + biodiversity began to recover in the Cenozoic era and the surviving mammals radiated into the terrestrial + aquatic niches once occupied by dinosaurs
• birds, descended from the only surviving dinosaurs, became aerial specialists

Question 12

End-Cretaceous EE: Biodiversity Dominance

Answer 12

• rapid dominance of flowering plants created niches for insects, birds, and mammals
• changes in animal species diversity late-Cretaceous + early-Cenozoic were promoted as continental plates slid to their current positions, moving/separating animals groups
• Early-Cenozoic, the evolution of grasses + coral reefs created entirely new ecosystems
• Late-Cenozoic, further extinctions followed by speciation occurred during ice ages that covered high latitudes in ice + retreated, leaving open spaces for colonization

Question 13

End-Cretaceous EE: Causes

Answer 13

cataclysmic impact of a large meteorite, or asteroid, off the coast of modern-day Mexico
- sharp spike in iridium levels at the rock stratum that marks the boundary between the Cretaceous + Palogene periods (usually only from space)
- aged + sized impact crater
- skies would have darkened + temps. would have fallen as the impact and ash blocked sunlight

Question 14

6th Mass Phanerozoic Extinction

Answer 14

Holocene/Anthropocene ME
- there are numerous extinctions of individual species recorded in human writings that mostly coincide with the expansion of European colonialism ~1500s
- accelerated since that time + is affected a broad swath of eukaryotic life including plants + animals both terrestrial and marine
- humans as a “GLOBAL-SUPER PREDATOR” that affects global ecology by hunting apex predators
- land use changes for development + farming that displaces species from their habitats
- large-scale impacts on the environment like widespread pollution, ocean acidification, and global warming

Question 15

6th EE Rates

Answer 15

• EE rates are hampered by the fact that most extinctions are probably happening without knowing it
• some estimate that the current mass extinction rate is 10-100 X higher than the rate of any earlier ME experienced in the history of life on Earth