History of life on Earth Mass Extinctions.

Agenda or Summary LayoutA summary of the topics discussed

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Explanation of Mass extinctions

The five major mass extinctions

Two particular extinctions

Sixth major extinction?

Mass Extinctions

Extinction refers to the death of all the organisms of a species so that not even a single member of the species exists.

Remember that there are two types of extinctions.

They are natural and man made extinctions.

Natural extinctions usually occur at a constantly lower rate, almost the same rate at rate at which new species are formed

But there are times when more than 50% of the earth’s species vanishes in a geological instant of a few million years.

This is called a mass extinction.

What are they?

The Five Major Mass Extinctions.

All five of the mass extinction events had the following in common:• At least 40% of all species disappeared in a short time (1

million years or less) and caused a dramatic drop in biodiversity

• Many different phylum became extinct whether big and well-established or small and localized

• It occurred world-wide, both on land and in water. Many ecosystems collapsed

• Most likely caused by the environment changing to fast for the organisms to adapt or evolve

The Five Major Mass Extinctions.

• End-Ordovician• 60% species (30% families)• 2 Short ice ages in succession• The earliest known mass extinction occurred about

439 million years ago and was caused by a drop in sea levels.

• The sea levels dropped because of the formation of glaciers.

• The sea levels rose as the glaciers started to melt.• Sea temperatures changed• Afterwards black anoxic mud covered the continents• Victims: marine invertebrates and coral reef

communities

The first mass extinction

The Five Major Mass Extinctions.

• The second extinction occurred about 364 million years ago (Late-Devonian).

• 70-80% species (20% families)• Series of glacial episodes changes sea levels,

temperatures and oxygen levels.• Possible asteroid impact• Victims: marine invertebrates, coral reef

communities, placoderms and other fish

The second mass extinction

The Five Major Mass Extinctions.

• The third extinction occurred about 250 million years ago (end-Permian).

• 90-95% species (56-60% families)• Global warming due to carbon dioxide increase

caused by volcanic eruptions. Mega-drought. Break down in ocean circulation leading to stagnation

• Victims: ferns, marina fauna, amphibians, reptiles, insectivorous tetrapods, insects, therapsids

The third mass extinction

The Five Major Mass Extinctions.

• The fourth mass extinction occurred about 199 million to 214 million years ago (Late-Triassic).

• 50% species (25% families)• It was caused when volcanoes erupted releasing

large amounts of lava. Global warming and dryness. Possible asteroid impacts.

• Victims: gymnosperms, therapsids and other tetrapods (replaced by dinosaurs), reef-dwelling invertebrates

The fourth mass extinction

The Five Major Mass Extinctions.

• The fifth mass extinction occurred about 65 million years ago (end-Cretaceous).

• 50% species (20-30% families)• Possible causes are: asteroid impact on the Yucatan

Peninsula which is in the Gulf of Mexico and volcanic eruptions. Nuclear winter followed by intense global warming.

• Victims: Dinosaurs, ammonites, marine reptiles, plankton groups

The fifth mass extinction

Two Particular Extinctions

Of the five mass extinctions two stand out .

These were the one that occurred 250 million years ago (3rd) and the one that occurred 65 million years ago (5th).

The mass extinction that occurred 250 million years ago was the most serious one.

The most famous mass extinction occurred 65 million years ago, the extinction of the dinosaurs.

Two Particular Extinctions

During this extinction almost 90% all species became extinct.

This included: 84% of marine genera and about 70% of land species plants, insects and vertebrate animals.

The mass extinction of 250 million years ago –the mother of all mass extinctions.

3rd Mass Extinction

• The End-Permian mass extinction brought the Palaezoic Era to a nasty end

• More than one pulse of extinctions

• Photosynthesis declined drastically and food pyramids collapsed word-wide

• Evidence from during this time found in rocks of the Great Karoo (drought)

3rd Mass Extinction

• Caused by global warming and drought

• May have been triggered by:

• Enormous volcanic eruptions in Siberia spewed over 2 million km3 of lava and pumped water, carbon dioxide and sulphur dioxide into the atmosphere. This increased greenhouse gases and perhaps caused acid rain.

• As the earth heated huge volumes of methane gas may have been released from frozen methane trapped in marine sediments. Methane speeds up global warming 12 times faster than carbon dioxide.

5th Mass Extinction

The dinosaurs appeared about 245 million years ago.

They flourished during the Jurassic Period.

This period occurred about 208 to 143 million years ago.

The dinosaurs dominated the land and air and some of them even lived in water.

5th Mass Extinction

Birds and mammals also existed during this time.

The dinosaurs then became extinct in a short period of 10 million years.

This occurred about 65 million years ago.

Of the marine families 16%, marine genera 47% and 18 % of the land vertebrate families also became extinct during this time.

5th Mass Extinction

Scientists are not sure about the exact cause of this mass extinction.

However the following are some of the conditions that occurred during this time:o there was a sharp drop in temperature.o the water of the seas evaporated .

The mass extinction of 65 million years - Causes

5th Mass Extinction

Many of the plants, the source of food for the dinosaurs died out.

Iridium was found in a thin layer of clay.

Iridium is an element that is very rare on earth but common in meteorites.

A huge crater was found in the Caribbean Sea.

There were many volcanic eruptions in India.

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The mass extinction of 65 million years - Causes

5th Mass Extinction

The above evidence lead to the formation of three hypotheses.

The most common hypothesis is that an asteroid (10-15 km in diameter) crashed into Earth, causing global climate change.

The climate change lead to the mass extinction.

The layer of iridium and the large crater in the Caribbean sea supports this hypothesis

The mass extinction of 65 million years ago – Hypothesis 1

5th Mass Extinction

This hypothesis deals with the continental drift theory, movement of continents away from each other.

It is believed that the continental drift led to the climate change.

The mass extinction of 65 million years ago- Hypothesis 2

5th Mass Extinction

This hypothesis deals with the volcanic activity in India.

It is believed that this volcanic activity released particles into the air.

These particles blocked out the sun for a long period of time.

This resulted in the lowering of temperatures on Earth.

Therefore many species died out because they could not adapt to the low temperature.

The mass extinction of 65 million years ago – Hypothesis 3

5th Mass Extinction

Scientists accept all three theories.

Mass extinction was caused by climate change.

The climate change was caused by the asteroid impact and volcanic activity.

The Holocene Epoch

The next major extinction is occurring presently.

Normal rate of extinction ia bout 10 species a year. We are currently losing 500 - 1 000 species a year.

This is the sixth mass extinction.

Human exploitation of the environment, overpopulation, destruction of habitats, pollution, global warming, unsustainable hunting (and pets) and invasive alien species is the cause of this mass extinction.

It is occurring in the Holocene Epoch and the mass extinction is called the Holocene extinction or sometimes the megafauna extinction.

Reason why it is called the megafauna extinction: the large mammals (woolly mammoth and dodo) became extinct during this time.

The sixth major extinction

Terminology

Extinction: refers to the death of all the organisms of a species so that not even a single member of the species exists.

Natural extinctions: usually occur at a constantly lower rate, almost the same rate at rate at which new species are formed.

Mass extinction: when more than 50% of the earth’s species vanishes in a geological instant of a few million years.

Jurassic Period: period when dinosaurs flourished.

Something for you to do

1. The process by which living organism die off so that not a single member of the species exists.

A. Mass extinctionB. ExtinctionC. Megafauna extinctionD. None of the above.

2. The disappearance of more than 50% of the Earth’s species in a geological instant of a few million years.

A. Mass extinctionB. ExtinctionC. Megafauna extinctionD. None of the above.

3. The name given to the extinction characterized by the death of large mammals.

A. Mass extinctionB. ExtinctionC. Megafauna extinctionD. None of the above.

4. The first mass extinction was caused by…

A. Drop in sea levelsB. Formation of glaciersC. Rising sea levels as the glaciers melted.D. All of the above.

5. The most famous extinction took place…

A. 65 million years agoB. 250 million years agoC. 364 million years agoD. 439 million years ago

6. The mass extinction that occurred as a result of unknown causes is occurred more than…

A. 65 million years agoB. 250 million years agoC. 364 million years agoD. 439 million years ago

7. The most serious mass extinction took places more than…

A. 65 million years agoB. 250 million years agoC. 364 million years agoD. 439 million years ago

8. Dinosaurs dominated the…

A. Water, land and airB. Water and airC. Land and airD. Water and land.

9. Iridium is…

A. A rare element found in asteroids.B. Found in the dinosaurs.C. A type of dinosaur.D. The sixth mass extinction.

10. The highest rate of mass extinction occurs during the…

A. sixth mass extinctionB. first mass extinctionC. second mass extinctionD. fifth mass extinction

Solution

1. B

2. A

3. C

4. D

5. A

6. C

7. B

8. D

9. A

10. A