Mass Extinctions

Define background extinction:

Low level extinction rate throughout history due to evolutionary and environmental processes.

Why are there 5 mass extinctions?

Across the Phanerozoic, 5 key events exist at a rate above the total regression line.

When did the End-Ordovician extinction occur?

444 mya

What % of species were lost during the End-Ordovician extinction?

86%

What is thought to be the cause of the End-Ordovician extinction?

Volcanic activity triggering global cooling and sea-level drops.

When did the End-Devonian extinction occur?

350 mya

What % of species were lost during the End-Devonian extinction?

75%

What is thought to be the cause of the End-Devonian extinction?

Evolution of forests reducing ocean oxygen levels due to changed nutrient delivery to the oceans.

Give some key losses of the End-Devonian extinction:

• Reef-builders

• Early tetrapods

• Placoderm fish

When did the End-Permian extinction occur?

250 mya

What % of species were lost during the End-Permian extinction?

94%

When did the Triassic-Jurassic extinction occur?

200 mya

What % of species were lost during the Triassic-Jurassic extinction?

80%

What was the cause of the Triassic-Jurassic extinction?

Sea-floor spreading in the Atlantic led to rapid volcanic outgassing and rising temperatures.

When did the K-Pg extinction occur?

65 mya

What % of species were lost during the K-Pg extinction?

76%

What was the cause of the K-Pg extinction?

The asteroid impact in Yucatan

Describe the iridium-based evidence for a meteor strike:

• Large majority of iridium delivered by extraterrestrial matter

• A massive spike in K-Pg era rocks (peaks at over 6x average)

What happened to fern abundance after the K-Pg extinction?

A brief explosion of coverage compared to other taxa.

Describe the Deccan Traps and how they contributed to the K-Pg extinction:

• A huge plateau of basaltic rock across middle-western India, up to 2km thick

• Formed after world’s 2nd largest land eruption

• Atmospheric CO2 spiked contributing to rapid warming

Name some key taxa lost during the End-Permian extinction:

• Blastoid echinoderms

• Rugose + tabulate corals

• Trilobites

How long is the sedimentary rock record gap for reefs after the End-Permian exinction?

7-8 million years

Name some key taxa that almost went completely extinct during the End-Permian extinction:

• Cephalopods

• Foraminifera

• Brachiopods

• Gastropods

Describe some of the key impacts of the End-Permian extinction on land:

• Significant loss of insects

• Large losses of gymnosperms

• 2/3 of amphibians, reptiles, and mammal-like reptiles lost

Describe the Siberian traps (End-Permian):

• 4 million km² volcanic deposits reaching 3.5km thick

• Eruptions persisted for 1 million years

Describe the change in ocean temperatures during the End-Permian extinction:

+10 degrees

Describe the change in ocean oxygen levels during the End-Permian extinction:

100-fold increase in anoxic regions (indicated by uranium isotope evidence)

Describe the change in ocean pH during the End-Permian extinction:

-1 pH unit

Give 3 key issues with comparing the Permian extinction to ours:

• Huge difference in rate of change (8C over 60,000 years)

• Different continent configuration (Pangaea more prone to desertification)

• Oceans more prone to deoxygenation