Mass Extinction Events

Question 1

When did the Great Oxidation Event occur?

Answer 1

2400 million years before present

Question 2

What caused the build up of oxygen in the great oxidation event?

Answer 2

Stromatolite algae

Question 3

What evidence is there of this oxidation event having occurred?

Answer 3

This is shown by bands of red iron oxides in marine rocks all over the planet

Question 4

What are mass extinction events?

Answer 4

They are punctuation marks in the history of the earth. It is a widespread and rapid decrease in the biodiversity on Earth

Question 5

When was the precambrian?

Answer 5

4500-570 MYBP

Question 6

When was the paleozoic era? Name the six epochs of this era.

Answer 6

570-225 MYBP; Cambrian Ordivician Silurian Devonian Carboniferous Permian

Question 7

Name the three epochs of the mesozoic

Answer 7

Cretaceous
Jurassic
Cretaceous

Question 8

Who coined the term the Anthropocene?

Answer 8

Paul Crutzen

Question 9

When do people think the Anthropocence began and why?

Answer 9

Maybe in 1610 because the old and new worlds swap DNA

Or on 16th July 1945 because that was when we were plunged into the Atomic age with the Trinity test

Question 10

What must happen for the Stratigraphy commission of the Geological Society of London to class an age as a new epoch?

Answer 10

1) Change the atmosphere’s composition, thus modifying plants
2) Change the distribution and diversity of plants, thereby changing the future fossil record
3) Acidify the oceans, which will modify mineral deposits in the ocean floor

Question 11

What are geological boundaries marked by?

Answer 11

Indicator fossils

Question 12

When was the first mass extinction of multicellular life?

Answer 12

In the early Cambrian (511 million years ago)

Question 13

How many species went extinct in the Cambrian MEE?

Answer 13

50% (mostly trilobites and brachiopods)

Question 14

What caused the Cambrian MEE?

Answer 14

We don’t have the exact mechanism here, but know that sulphur entered the atmosphere in huge amounts and that high levels of H2S coincided with low oxygen levels.

Question 15

When did the Permian MEE occur?

Answer 15

252 million years ago

Question 16

How many species died in the Permian MEE?

Answer 16

More than 95% of marine species and 70% of terrestrial species like gorgonopsian reptiles

Question 17

What caused the Permian MEE?

Answer 17

Sediments around the boundary show signs of anaerobiosis, and there is a strong suggestion that oxygen tensions fell so low that life became impossible for many life forms.
There is no meteor crater whose date fits, but definite synchronous large volcanic eruptions (forming the Siberian traps).

These volcanic eruptions released CO2 and caused temperatures to rise by 3-9 degrees celcius, leading to CH4 being released from sediments which altered atmospheric chemistry.

Question 18

How can we tell the difference between the permian and triassic boundaries?

Answer 18

Deposits in Japan and parts of China are red radiolarian cherts for millions of years but the get darker the closer they get to the P/T boundary (due to losing Fe3+ and SiO2) The PT boundary is marked by black shales that indicate anaerobic conditions

Question 19

What is a clathrate?

Answer 19

CH4 will become locked into water ice as a clathrate – ‘burning ice’

These clathrates are stable for millennia if cold, but if warmed (>18oC) become unstable and de-gas.

Question 20

How is methane released after warming?

Answer 20

Extensive beds of methane build up in oceanic sediments as clathrates, then are disturbed by volcanism. This has two effects: physical disturbance, and global warming (via CO2 – from volcanoes). Once enough methane is disturbed the system becomes self-reinforcing, climatic warming releasing more CH4, until a large proportion of methane in sediments is released. The transient spike of CH4 may only last a few decades, but will deliver a huge warming pulse while reducing oxygen levels; it decays into CO2 that leaves a warming signal for centuries.

Question 21

What is an effect of warmer seas?

Answer 21

Reduced circulation, meaning more stagnant deep zones resulting in anoxia

Question 22

What is euxinia?

Answer 22

Euxinia is the state where free H2S occurs; it is diagnostic of anoxic conditions. In such conditions green sulphur bacteria develop; their biomolecules (isorenieratene) turn up in the black shales that abound in oceanic anoxic events. Hence we know the seas were not just full of black smelly sediments at depth, but even sunlit waters were oxygen-free. This means very low O2 in the air, even toxic H2S emissions.

Euxinia was found in the photic zone after the P/T MEE, lasting for a few million years.

Question 23

When did the K/T mass extinction event occur?

Answer 23

65 million years ago

Question 24

Which is the only boundary to be observed across the whole globe?

Answer 24

The K/T boundary

Question 25

What evidence supports the theory that an asteroid was responsible for the K/T MEE?

Answer 25

The K/T boundary was enriched in Iridium 10-15 background levels all over the planet, an isotopic signature that matched an asteroid.

Question 26

Why was the catastrophist theory of dinosaur extinction doubted at first?

Answer 26

There was no impact crater

Question 27

Where was the impact crater eventually found for the K/T MEE?

Answer 27

oil surveys in the gulf of Mexico revealed a huge impact structure (The Chicxulub crater, 160Km diameter) extending from a ground zero on the Yucatan peninsula.

Question 28

What is the evidence that supports the Chicxulub crater site being the actual crater site?

Answer 28

The date of this crater worked out around 65MYBP, and the scale fitted nicely with the impact of a 10km asteroid hitting the earth at 15km per second. All the evidence is concordant with this impact site: depth of ashy layer is greatest closest to this site as is incidence of shocked quartz (only formed under immense pressures, not volcanoes).

Question 29

What is the evidence against the asteroid theory?

Answer 29

1) Some doubt regarding Chicxulub crater (it might be a bit early, but resolving such sharp boundaries is an issue)
2) There are three other craters: Shiva crater off West India, Boltysh crater in Ukraine and Silverpit crater under the north sea.

However, a plausible explanation is a multiple impacts from the synchronised disintegration of a large body.

Question 30

How might volcanoes be involved in the K/T MEE?

Answer 30

Deccan traps of northern India poured out a massive series of eruptions that must have blocked light and reduced temperatures globally for long periods.

However, there is no proof to associate the eruption with the impact – in fact the eruptions seems to have come first. No methane event or anaerobiosis seems to have happened here.

Question 31

How did the 10km diameter asteriod impacting the Yucatan peninsula affect the climate?

Answer 31

The geology of this area is carbonate rocks with sulphates – fossil sea bed and evaporites.

This is profoundly important as significant amounts of CO2 and SO2 are expelled from the deposits, enough to destabilise the climate.

In addition there is an immense amount of stony debris thrown skywards; this plume encircled the earth, and would have been red hot at first.

Question 32

What happened between 0-24 hours after the impact of the asteroid? (K/T MEE)

Answer 32

Phase 1: 0-24 hours (ish) red hot debris appears in the sky, cooking exposed surfaces. Due to high oxygen levels (>30%), fires would have swept the planet.

Question 33

What happened between 0-2 years after the impact of the asteroid? (K/T MEE)

Answer 33

Phase 2: 0-2+ years: little sunlight reaches the earths surface due to atmospheric debris plus sulphate aerosols.

Question 34

What happened when the debris finally cleared after the K/T asteroid impact?

Answer 34

Phase 3: As the debris cleared, the elevated CO2 caused a dramatic warming in climate. It was probably too late for the terrestrial archosaurs by then, but this would certainly have ensured that climatic patterns took some millennia to settle down to previous patterns, if they ever did.

Question 35

What does PETM mean?

Answer 35

Palaeocene-Eocene Thermal maximum

Question 36

When did the PETM MEE occur?

Answer 36

55 million years ago

Question 37

What caused the PETM?

Answer 37

Spike in temperature. We don’t know why this happened.

Question 38

What is the evidence for a spike in temperature in the PETM MEE?

Answer 38

O16:O18 ratios show that sea temperatures raised by 8C in a few kyrs (10C at antarctic sea surface)

this was associated with changes in oceanic algae, and the replacement of early mammals with modern families. Subsequently there was a phase when the arctic sea was full of the tropical freshwater fern Azolla!

Question 39

Why did oxygen tensions fall during the PETM MEE?

Answer 39

C13: C12 ratios plunged, suggesting that a pulse of C12-rich gas infused the atmosphere. Oxygen tensions also fell, leading to a model that C12-rich methane eruption led to another methane catastrophe. Models suggest that [CO2] was 2000-3000 ppm. The seas were acid, leading to a replacement of chalky stones to red clays (too acid for calcareous microplankton).

Question 40

What evidence is there of another major impact occurring 12900 years ago?

Answer 40

There was – probably - another major impact c. 12900 years ago. A layer of diamonds (26 sites in Europe and North America), iridium, and helium-enriched fullerenes showed a carbon-rich body 2-3km across hit earth. This co-incided with the sudden and mysterious collapse of american Clovis stone age cultures, mastodons and mammoths.

In the americas this was a clear sharp black line with megafauna bones below it, and none above. It’s not so sharp in Europe, but there was a huge climatic effect.

Question 41

Why was there a cooling event after the impact in 12900?

Answer 41

The impact seems to have been on the Laurentide ice cap, causing a huge surge of freshwater to enter the atlantic and switch off the gulf stream – the Younger Dryas cooling. This gives us a new boundary – the YDB. (An old UK name for this boundary is the Loch Lomond stadial).

Question 42

When was the Pleistocene-Holocene MEE?

Answer 42

around 10,000 years ago

Question 43

Why was the Pleistocene-Holocene MEE odd?

Answer 43

all other MEEs removed small animals as well as large –the Pleistocene event was a selective removal of large species.

Mammoth, giant elk, sabre-toothed tigers, dire-wolves… The threshold for removal is said to be 60Kg, but don’t worry about this figure too much.

Question 44

What caused the Pleistocene-Holocene MEE?

Answer 44

Our ancestors (hunting)

Question 45

What evidence is there that our ancestors hunted mammoths?

Answer 45

In the Ukraine a 15000 year old village has been excavated, where all the buildings were mammoth bone, probably covered in mammoth hide.

Question 46

Wherever humans go, giant animals disappear. Give examples of some of these animals.

Answer 46

Mammoth in Asia

Giant marsupials in Australia

Giant lemurs in Madagascar

Giant ground sloths in South America

Giant Moas in New Zealand

Question 47

Where is the strong hold for surviving large megafauna and why might this be?

Answer 47

(Interestingly, the stronghold for surviving large fauna is in Africa, where humans evolved. Perhaps they learned to fear humans before humans became too effective at hunting?)

Question 48

Give an example of how removing megafauna also removed non-target species.

Answer 48

New Zealand had the largest eagle known, adapted to eating Moas – when the Moas became extinct so did Haast’s eagle Harpagornis moorei. (This was the top predator - 10% of the 80-100 kg range moa pelvis had eagle claw marks!)

Question 49

What happened to the passenger pigeon?

Answer 49

This bird was once the commonest bird on the planet, >5000 million, with flocks 1 mile wide * 300 miles long that took a day to fly past.

They fed on acorns etc in the oak woods of north america, but were hunted as cheap meat for slaves, undergoing a slow decline up to 1870, followed by a catastrophic collapse 1870-1890, by which time the species was lost. The last, Martha, died in Cincinnati zoo 1-9-1914.

Question 50

Why did the Chinese freshwater dolphin go extinct?

Answer 50

This wasn’t meant to happen, it’s just that no-one got around to stopping the destruction of the Yangtze river ecology by an explosion of heavy industry. Also threatened by this same damage are a freshwater porpoise (a few in zoos) and the only alligator in the old world.

Question 51

Name the only mammal endemic to the Great Barrier Reef that went extinct and explain why.

Answer 51

The Bramble Cay Melomys (it was a rat)

Bramble Cay island got repeatedly flooded after sea level rise.

Question 52

Why might we be experiencing an MEE now?

Answer 52

1) Large fossil animals cease as the plastic era dawns (this will be noticed in the fossil record)
2) Although oceanic algae haven’t changed much yet, the North Sea algae have changed.
3) We are pumping CO2 into the atmosphere at an exponentially increasing rate

Question 53

Explain what is going to happen if we don’t do anything to change our ways.

Answer 53

1) Change in climate patterns (increases in extreme events, especially floods and storms)
2) Acidification of the sea water from CO2 dissolution
3) Positive feedback loops (warmth leads to release of greenhouse gases, leading to more warming)
4) Ice retreats and exposes dark land - absorbs heat and warms further.

Question 54

When has the rate of accumulation of CO2 been highest?

Answer 54

Now. There appears to be no period in earth’s history when the RATE of accumulation of CO2 has been so high.

Geological records show intense vulcanism tends to be followed by anoxia/marine extinction events, ‘reef gaps’ and evidence of CH4 degassing.
The problem comes if/when we lose planetary control, to the extent of methane degassing.

Question 55

What will happen if warming continues to different species?

Answer 55

Cold adapted species will vanish (no arctic or antarctic ice)

Tropical forests will be lost in fires (adding more CO2) and this will wipe out thousands of species

Will society exist in a stable form when most farmland is unusable

Question 56

How might geo-engineering save us?

Answer 56

Why not install a sunblock?! Orbiting mirrors could reflect away enough heat to offset the enhanced greenhouse effect

There must be some catches, but so far the idea has not been ruled out on theoretical grounds. Who controls the satellites??