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Environments through time: 5. Past extinction and mass extinction events
Extract from Earth and Environmental Science Stage 6 Syllabus (Amended
October 2002). © Board of Studies, NSW
[Edit: 24 Jul 08]
Prior Learning: Preliminary Module 8.2 (subsection 5).
Science Stages 4-5 syllabus: Outcome 5.8 (content: 5.8.3, the theory of evolution and natural selection), Outcome 5.9 (content: 5.9.4, natural events).
Background information: Extinction can be defined as the time
at which species cease to exist. It is considered to be a natural event in the
history of life on Earth. What
triggers mass extinctions? 
by Charles Q Choi, MSNBC Technology and Science,
8 Aug 2007, covers all the mass extinctions and some of the theories proposed
to account for these extinctions.
gather, analyse and present information from secondary sources to compare two different concepts used to explain mass extinction events
- You need to gather information about concepts that have been used to explain mass extinction events. A concept could be an idea, a theory or an explanation. You could consult websites, scientific journals or textbooks.
- Identify two concepts
- Analyse the information you have gathered by identifying chains of cause and effect statements. This will show how each concept is believed to have caused mass extinctions.
- Compare the two concepts according to how well each relates the information.
- Explain how the data refutes or supports each hypothesis.
- Present information in a way that shows the similarities or differences between the concepts. Some ways of presenting the information include tables, Venn diagrams or flow charts.
| Name | Bolide impact | Volcanic activity |
|---|---|---|
gather information from secondary sources and use available evidence to identify the relationship between mass extinctions and the divisions of the geological time scale
- Gather information about the times when mass extinctions occurred. You can use the graph of Last appearance of taxa (a group of organisms) below to help with the information.
- On the Geological
time scale Enchanted Learning, USA, indicate where each mass extinction
took place.
- Using this information, identify the relationship between the mass extinctions and the divisions on the geological time scale.
compare models of explosive and gradual adaptations and radiations of new genera and species following mass extinction events
- Gradual evolution, as proposed by Charles Darwin, is a process of slow and gradual change at a constant rate. The number of species increases steadily.
- Explosive evolution is characterised by periods of low and gradual change, followed by periods of rapid change and diversification, with a rapid increase in the number of species.
- If the mass extinction events are mapped on the diagrams below it can be seen that even though some groups of organisms become extinct, there has also been some rapid evolutionary radiation after a mass extinction event.
- Surviving groups of organisms have substantially increased in numbers or there has been a radiation of the types of living organisms inhabiting the Earth.
distinguish between mass extinctions and smaller extinctions
- A mass extinction is the extinction of a large number of groups of organisms over a large area. Mass extinctions are usually relatively sudden in geological terms, i.e. they occurred over a few million years at most and in some cases much less than that.
- A smaller extinction involves the extinction of a small number of groups of organisms in a local area. Smaller extinctions are caused by local ecological disturbances.
explain the recent extinction of the marsupial, bird and reptile megafauna in Australia, as an example of smaller extinction events involving several large species
The Australian megafauna
- The Australian megafauna (large animals) became extinct between 60 000 and 20 000 years ago. Some examples of the megafauna include Procoptodon, a 3 metre tall short face kangaroo, Diprotodon, a wombat like creature the size of a hippopotamus, Genyornis, a very powerful 2-3 metre high flightless bird and Megalania, a 5 metre long goanna.
- This is a small extinction as only a small number of
species died out (around 40) and it was restricted to the
Australian continent. There were many other smaller animals that
survived.
Australian megafauna Prehistoric life, Museum Victoria
compare these smaller extinction events with widespread ‘catastrophic’ events in which entire ecosystems collapse with the extinction of many entire classes and orders
| Smaller extinction events | Catastrophic events |
|---|---|
| only local ecosystems and/or niches within an ecosystem are affected | entire ecosystems collapse |
| about 40 Australian megafauna species became extinct | many entire orders and classes become extinct |
| caused by small scale ecological disturbance such as introduction of a new species or local climate change | caused by some natural catastrophe, e.g. meteorite impact, sea level change or global climate change. |
- The Extinction Files discuss a number of theories as to the causes of mass extinction events.
-
Extinction Australia's biodiversity, Australian Museum, Sydney discusses
whether we are witnessing the sixth mass extinction.
analyse information from secondary sources on at least two different hypotheses used to explain the extinction of the megafauna
There are at least TWO hypotheses used to explain the extinction of the megafauna. In recent years this has been the subject of some controversy amongst scientists.
One hypothesis is based on the premise that the extinctions commenced after the arrival of humans in Australia. It proposes that hunting, perhaps combined with ecological disruption by deliberate burning, was the main cause.
Gather information about the extinction of the megafauna from secondary sources such as
The Future Eaters - Taming the Fire describes the theory of extinction by human interference.
Another hypothesis is that climate changes in the Late Pleistocene, when the world cooled in the ice ages, were the cause, as the continent of Australia dried out and became arid. If you search the internet you will find that evidence from Cuddie Springs, in north western NSW, has been interpreted in two different ways, supporting two different hypotheses about the extinction of the Australian megafauna.
Megafauna ,
The Australian Museum. In this article Stan Florek indicates that the extinction
of the megafauna was not due to humans but due to environmental factors.
List two hypotheses and identify how the data supports or refutes each hypothesis.
You may wish to structure your work as follows:
Hypothesis 1
......................................................................................................................
Data supporting hypothesis
......................................................................................................................
......................................................................................................................
Data refuting hypothesis
......................................................................................................................
......................................................................................................................
Hypothesis 2
......................................................................................................................
Data supporting hypothesis
......................................................................................................................
......................................................................................................................
Data refuting hypothesis
......................................................................................................................
......................................................................................................................
Conclusion
Indicate which hypothesis best fits the data
......................................................................................................................
......................................................................................................................
assess a variety of hypotheses proposed for the mass extinctions at the end of the Permian and at the end of the Cretaceous
- To assess these hypotheses you will need to look at
the evidence available and make a judgement to how plausible the
explanation is.
- The End Permian mass extinction was the largest
with around 95% of life becoming extinct. This mass extinction is
explained by the extreme climate change model. The theory put
forward to account for this extinction is that for around 40 000
years the Earth went through a period of extreme cold (ice age)
followed very soon by extreme heat (super greenhouse) and very
few forms of life were able to cope with the extremes of
climate.
- The evidence for this theory comes from Greenland and Russia. The sequence of rocks in Greenland gives a very good coverage of the time span of the extinction, showing three major events.
Event 1: A cooling of the earth and the loss of much of the life on land. This corresponds to a massive (up to 10 000 year) eruption of volcanoes in Siberia, known as the Siberian Traps. These eruptions would have first blocked out the sun with ash and cooled the planet.
Event 2: As the ash settled, the carbon dioxide released from the eruptions caused a greenhouse effect. The oceans warmed and became anoxic killing marine life.
Event 3: Resulted from the warming of the oceans. A release of dissolved methane sent the earth into a super greenhouse. Evidence for this is seen in an increase of carbon 12 isotopes in the sediment from this time. The overall rise in average global temperature could have been 10 degrees and that is enough to kill almost everything.
- The Permo-Triassic
Extinction, Department of Earth Sciences, University of Bristol, UK, website
offers an excellent description of some of the theories behind the mass extinction.
- The End Cretaceous mass extinction claimed around 75% of life on Earth,
the most famous species being the dinosaurs. The theoretical explanation for
this mass extinction is that a large rock 10-15 km across (bolide) crashed
into the Earth and disrupted the climate. Evidence which supports this theory:
A large crater of the right age has been found on the Yucatan Peninsular in
Mexico. A dark layer containing high levels of carbon (charcoal) and iridium
occurs at the Cretaceous-Tertiary boundary all over the world. Iridium is
not common in the crust but is common in meteorites. A massive volcanic eruption
in India (known as the Deccan Traps) occurred at the same time.
Dinosaur mass extinction Museum Victoria
- The bolide would have crashed into the Earth. The shockwave produced would
have wiped out all living things within 5000 km of the impact site. A cloud
of dust and debris would have enveloped the Earth blocking out the sun and
stopping plants from photosynthesising, cutting the food chain at the bottom.
Flying hot rocks would have started massive forest fires across entire continents.
The vibration of the impact would have echoed through the earth to culminate
on the opposite side and tear it apart, causing prolonged volcanic eruption.
The Earth would have experienced a nuclear winter that would last for decades.
Only those animals and plants that had means of insulation or were able to
hibernate would survive.
- Extinctions:
Cycles of life and death through time looks at the causes and effects
of the mass extinctions that occurred through the Phanerozioc. Hooper Virtual
Paleontological Museum, Canada
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