Lecture 24: Mass Extinctions

Question 1

what are extinctions and why do they matter?

Answer 1

extinctions occur when the last individual of a species dies out, often because the environment of said species changes faster than it can adapt

extinctions can be local, widespread, or global

Question 2

what are some causes of extinctions?

Answer 2

plate tectonics and sea level changes

volcanic activity

climate change

extraterrestrial (asteroid/comet impact)

Question 3

what is the general trend of animal diversity over time?

Answer 3

one long-term increase, punctuated by sharp declines, then followed by recoveries and radiations

Question 4

what is 2 pieces of evidence for the role of an impact at the end Cretaceous?

Answer 4

fern spike/ pollen trough:
- iridium spike in clay causing a drop in pollen, increase in ferns
- records death of flowering plants and fern early recolonisation of land after impact winter

shocked quartz in K-T boundary clay:
- shock wave from the pressure caused by the impact, altering rocks
- very high temp and pressure
- planar deformation features (PDFs) are linear-like features found in quartz, and suggest shock alteration of quarts caused by impact

Question 5

how does a hypothesis link an iridium layer with asteroid extinction?

Answer 5

alvarez hypothesis

a thin clay layer at the K-Pg boundary is unusually rich in iridium

global distribution and enrichment of iridium suggest a single, massive asteroid impact

Question 6

what are some causes of other extinctions, like the end-permian extinction, and the possible role of volcanism?

Answer 6

end-permian:
- coincided with final assembly of pangaea and eruption of siberian traps
- volcanism caused rapid global warming, ocean anoxia, ocean acidification…

late devonian
- onset of glaciation could be linked to first forests

Question 7

how do we avoid impact-induced extinction?

Answer 7

nasas dart mission

first ever demonstration of a kinetic impact technique to deflect an asteroids orbit

using a spacecrafts impact to change an asteroids trajectory

Question 8

what is a multi-planet species, and the main concept behind it?

Answer 8

main concept is spreading our species over more than just earth, to ensure that a catastrophe on earth wouldn’t mean extinction

multiplanet presence prevents extinction, or provides redundancy against collapse in one location