The K-Pg Extinction (final exam) Flashcards
Describe the Mesozoic Climate and Paleogeography that led to the K-Pg extinction?
- climates were mostly equable during the Mesozoic
> lacked strong N-S zonation characteristics of modern day - Pangaea persisted as a supercontinent during most of Triassic > climates were warm and tropical with some arid regions and temperate poles
- Laurasia fragmented by Late Jurassic
- Mild climates persisted into Jurassic
> ferns existed at higher latitudes
> dinosaurs widespread across Laurasia and Gondwana - by Cretaceous, climates were more strongly zoned than Jurassic, but still pretty equable until end of Mesozoic
What is the significance of the end Cretaceous extinction?
- the end Cretaceous extinction is one of the 5 largest in the history of life
- only the end Permian extinction was more devastating to global diversity
- Cretaceous was more rapid than the permian though
- extinctions hit both land and sea fauna
Who was most affected by the Kpg extinction and who survived?
Non-avian dinosaurs, pterosaurs, marine reptiles, ammonites, and rudist bivalves all died out
> 80-90% marine species were lost
Survivors:
- avian dinosaurs, crocodiles, mammals, amphibians, fish
What are the examples of the different theories (proven or not) for the causes of the dinosaur extinction?
Biting insects carrying diseases that killed dinosaurs over millions of years
Competition with mammals, who outcompeted dinosaurs for niches and/or ate their eggs
The evolution in plants of substances poisonous to dinosaurs
Falling sea level produced loss of habitats
Impact of a meteorite
The sun became too bright and dinosaurs were blinded
Allergies from flowering plants
Dinosaurs were too specialized and could not adapt to changing environments
What are the theories for the Cretaceous extinction that we actually have good evidence for?
- meteorite or asteroid impact causing widespread climatic change
- massive volcanic eruptions in India causing atmospheric disruptions
- global marine regression causing harsher, more seasonal climates
Explain the meteorite impact theory and what is the evidence supporting it?
A meteorite or asteroid impact caused widespread climatic change (widely accepted theory)
- known as the Chicxulub crater
- initially based on 2.5cm iridium layer first identified in Italy, now found around the world
Iridium:
- very rare on Earth but very abundant in meteorites so this supports the theory - erected debris from the asteroid caused the iridium layer
- tektites (natural glass produced by melting rocks during impact) found globally with this layer
- shocked quartz (another impact feature with cross-hatched lines)
- soot layers associated with the iridium layers in some localities indicated widespread fires (some studies suggest surface temp was 80-90 celsius for a day or two)
Describe the size/speed/power of the Chicxulub crater asteroid
About 10-15km wide, twice the size of Mount Everest
Was moving at 20km/s or about 60x the speed of sound
Power equivalent to 1-10 billion atomic/nuclear bombs
What is the Tsunami evidence for the meteorite / asteroid impact theory?
Tsunami deposits (Tsunamites) prevalent around Chicxulub
- evidence of almost global tsunami activity at the end of the Cretaceous
- the initial wave height of the tsunami would’ve been about 4.5km - very large
What were some of the effects of the meteorite impact (shorter and longer term)
Blocking of sun:
- 60x mass of meteorite ejected into atmosphere - 10 km diameter meteorite
- heat of impact caused massive wildfires
- temporarily halted photoynthesis
- months of global cooling
Acid rain:
- vaporized rock and atmospheric gases mixing > sulfuric and nitric acid
Delayed greenhouse warming
What are the overall extinction rates comparing lifestyle and habitat? (in terms of survival)
Survival:
Mostly aquatic habitat compared to terrestrial
Most Ectothermic compared to Endothermic
Mostly small bodied > can burrow or hide under objects to escape being cooked like the bigger dinos
Non-amniote compared to amniote
Those that can hibernate generally did better
Explain how the Deccan Trap flood basalts could be a cause of the extinction?
The Deccan Traps are large-scale volcanic eruptions in India
- eruptions occurred during the Cretaceous
- some believe they would’ve released large quantities of gases like carbon dioxide and sulfur dioxide, leading to climate change and possibly contributing to the extinction event
- some also think the meteorite impact might have triggered the eruptions
- lots of hot spots and flood basalts in India
Explain the theory that dinosaurs were already in decline before the extinction?
Idea that dinos were already in decline and that the meteorite impact was just the final nail in the coffin
- Globally, the diversity of dinosaurs was lower than before the Cretaceous
- Less diverse habitats = dinos becoming less diverse = less of a buffer to survive extinctions
- Anything as big as a T-rex that require so much food are going to struggle with environmental changes
*in reality, the meteorite impact was probably THE causal factor in the extinction of the non-avian dinos
Explain the seasonal impact/element of the extinction
New study suggesting the impact happened in spring in North America, when many organisms were getting ready for the reproductive season > so plants and animals had a harder time recovering in NA
Plants and animals in southern hemisphere recovered faster because it was autumn there (animals already starting hibernation)
- evidence comes from impact spherules in gills (fish) and from carbon isotopes
