The End Cretaceous mass extinction

Question 1

What is another name for the End Cretaceous mass extinction? Give 2 alternatives.

Answer 1

1. The K/T event: the ‘cretaceous/tertiary’

2. The KPG event: the ‘cretaceous-paleogene’

Question 2

When did the KPG event occur?

Answer 2

66 mya.

Question 3

What percentage of species were wiped out?

Answer 3

75%.

Question 4

Define the Maastrictian stage.

Answer 4

The last 5 million years of the cretaceous.

Question 5

Give examples of dinosaur groups thriving in the Maastrictian. List 4.

Answer 5

1. Tyrannosaurs
2. Saurpods
3. Hadrosaurs
4. Ceratopsians

Question 6

Giant pterosaurs were also thriving in the Maastrictian. Why not smaller species?

Answer 6

They had been outcompeted due to the evolution/radiation of birds.

Question 7

List 4 groups that survived the KPG event.

Answer 7

1. Crocodiles
2. Amphibians
3. Placental mammals
4. Birds

Question 8

How is it supposed that crocs and amphibians survived the KPG event?

Answer 8

They are freshwater animals: nuclear winter effect from meteorite kills plants, forming detritus. Detritivores thrive, thus so do small carnivores (amphibians), in turn providing food for larger carnivores (crocs).

Question 9

The placental mammals radiated after the KPG. What happened to the marsupials?

Answer 9

They suffered a large reduction in diversity.

Question 10

The placental mammals and birds radiated after the KPG. What explanation is there for this?

Answer 10

They are both endothermic: on the one hand makes them vulnerable as need more energy and food, however they are able to sustain locomotion. This means they have increased dispersal ability - basically they can run away.

Question 11

Why was it beneficial that mammals and birds are smaller than dinosaurs in the KPG event?

Answer 11

They could find shelter or hide in burrows, dinosaurs couldn’t.

Question 12

What are the 3 main hypotheses for the KPG event?

Answer 12

1. Meteorite
2. Flood volcanism
3. Plate tectonics and gradualistic climate change

Question 13

In the meteorite hypothesis, earth could have been hit by a) a meteorite or b) a comet. Explain the differences between these impacts.

Answer 13

a) Would have been larger and travelling slower than a comet, ~30,000kph
b) Would have been smaller and travelling faster, ~50,000kph

Question 14

Earth was hit by only 1 meteorite/comet. True or false?

Answer 14

We don’t know, there may have been multiple impacts.

Question 15

What would have happened upon meteorite impact?

Answer 15

1. Kinetic energy causes material to be thrown into the air, creating a crater
2. Crater is unstable and collapses
3. Rock and water pulverised/vaporised, more matter sent into the air. This blocks out the sun in a nuclear winter effect. This prevents photosynthesis.
4. Tsunamis occur globally

Question 16

What physical evidence is there of a meteorite impact?

Answer 16

A crater: The Chicxulub crater on the Yucatan peninsula, Mexico is the correct age and size.

Question 17

How does iridium serve as support for the meteorite hypothesis?

Answer 17

Ir is a deep crust metal, however it is present in clay dating to the KPG boundary. Suggests it was thrown up by the blast.

Question 18

How does shocked quartz serve as support for the meteorite hypothesis?

Answer 18

Mineral of the correct age presents laminae (stress markings) that suggests impact.

Question 19

How do microketites serve as support for the meteorite hypothesis?

Answer 19

Microketites are super-cooled glass structures that radiate out from an explosion.

Question 20

What evidence of tsunamis is there that can be attributed to meteorite impact?

Answer 20

In Texas: water was 1km in height and flowed 10s of kilometres inland

Question 21

There was a spike in fern pollen around the time of the KPG event. How is this evidence for the meteorite hypothesis?

Answer 21

Ferns thrive in low light intensity and would thrive in a nuclear winter scenario.

Question 22

India used to be a separate island located on a major hotspot. How do we know this?

Answer 22

The ‘Deccan traps’ of the west-central plateau are volcanic deposits

Question 23

What evidence of flood volcanism is there around the time of the KPG event? Give 3 examples.

Answer 23

1. The Deccan Plateau
2. The presence of Iridium dragged up by magma flows
3. Acid rain caused by pyroclastic flow

Question 24

How could SO2 ejected from volcanoes affect the global climate?

Answer 24

In excessive quantities it can cause global cooling, which may have lead to extinction.

Question 25

How might plate tectonics and gradualistic climate change have caused mass extinction?

Answer 25

May have lead to global cooling: large-bodied dinosaurs would not survive this.

Question 26

What support is there for gradualistic climate change? Give 3 examples.

Answer 26

1. A major cooling event in the oceans of the Campaignian (80my before the Maastrictian).
2. Gradual extinction up to the KPG boundary of marine species, e.g. ichthyosaurs and ammonoids
3. Reduction in sea-floor spreading rate affects oceanic circulation, which can cause cooling.

Question 27

How long would ‘gradualistic’ climate change have taken?

Answer 27

Millions of years.

Question 28

In fact it is hypothesised that a combination of both a) meteorite impact and b) flood volcanism are responsible for the KPG event. Where did they both occur?

Answer 28

a) The northern hemisphere

b) The southern hemisphere

Question 29

Explain the ‘press-pulse’ hypothesis for mass extinction.

Answer 29

‘Press’ = a long term event that puts an ecosystem under stress.

‘Pulse’ = a sudden, short-term event not extreme enough to cause extinction alone but serves as ‘the straw that broke the camel’s back’ for an already vulnerable ecosystem.

Question 30

What is the a) press and b) pulse when applying the hypothesis to the KPG event?

Answer 30

a) Flood volcanism, that appears to be present in all major extinctions throughout history
b) The meteorite impact