Download 1. Evidence for the rearrangement of crustal plates and continental

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Evolution of Australian Biota
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1. Evidence for the rearrangement of crustal plates and continental drift
indicates that Australia was once part of an ancient super continent
The main continental plates of the earth’s crust are only about 60 km thick and “float” on the semi-liquid mantle layer
underneath. As convection currents move within the mantle the crustal plates move slowly on the surface (up to 10 cm
each year). Sometimes the plates bump into each other, e.g. Australia into Asia or Africa into Europe. Some plates slide
past each other, e.g. Pacific Ocean plate is sliding north relative to the North American plate; California has many
faults, earthquakes and some volcanoes. In some places the plates are pulling directly apart, e.g. South America broke
away from Africa and the gap between is the Atlantic Ocean. Africa has the “Great Rift Valley” crack from north to
south where it is beginning to split apart; it will take many millions of years to separate completely. It is possible to
“jigsaw puzzle” most of the southern continents back together to form Gondwana as it probably was 100mya. There is
considerable evidence that the climates have not always been the same as today; Antarctica has large areas of coal and
fossils of marsupials implying much warmer climates than today. It is also possible that Gondwana was not always near
the earth’s south pole.
These drawings by the German Scientist, Alfred Wegener in 1929
were part of his theory of Continental Drift. Unfortunately
Wegener had no convincing way of explaining how the continents
move. Most Geologists dismissed the theory but many Biologists
were interested because it did help to explain the distribution of
many plants and animals across the southern continents. Deep
ocean surveys in the 1950s showed that the depth of sediments
were very, very, thin if the oceans were billions of years old like
the continents. Mid-ocean volcanic ridges were mapped that
could explain seafloor spreading. In the 1960s and 70s magnetic
mapping of lava on the sea floor showed bands that appeared to
match changes of the earth’s magnetic field. The bands showed
younger rocks near the mid-ocean ridges, and the oldest rocks
near the edges of the continents. Convection currents in the
mantle could push the continents. By 1980 Continental Drift was
accepted by nearly all scientists. Compare these drawings with
the animations at the web site below … they are not perfect but
they are very good considering they were 70 years earlier.
Students learn to:
● identify and describe evidence that supports the assertion that Australia was once part of a landmass called
Gondwana, including:
Animations showing the breakup of Gondwana are available at
http://kartoweb.itc.nl/gondwana/gondwana_gif.html
http://earth.leeds.ac.uk/~greg/Gond.html
– matching continental margins
It is possible to “jigsaw puzzle” most of the southern continents back together to form Gondwana as it probably was
100 mya. You did this in Year 9 or 10. Remember that the coastlines might have changed enormously since the breakup
of the continents as a result of erosion, volcanic activity and changes of sea level. Tasmania for example is really part of
the landmass of Australia. It has only been an island for a few thousand years since the oceans rose. It is more useful to
jigsaw the continents with their continental shelves. Both animations above include the continental shelves.
David Dobeson
2005
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– position of mid-ocean ridges
Mid-ocean ridges have formed from the volcanoes that spewed up as the plates have moved apart; e.g. between South
America and Africa and between Antarctica and Australia. The volcanic vents in the mid ocean ridges are now known
to have their own ecosystems based on the energy of the volcanic chemicals trapped by chemosynthetic bacteria. There
are earthquakes near mid-ocean ridges but many less than near other plate boundaries.
This map from the US Geological Service shows the locations of significant earthquakes from 1990 to 2000. Many
maps of mid-ocean ridges show a zig-zag line rather than a single ridge line.
Our geological plate, called the Australian-Indian Plate is moving north at about 7 cm each year. We broke away from
Gondwana about 45 million years ago. South of Australia along the mid-ocean ridge is where the seafloor is spreading.
From New Zealand to New Guinea the eastern edge of our plate is colliding with the Pacific Plate. Near Indonesia, the
northern edge of our plate is sliding under the Asian Plate. Nearly all of the earthquakes shown on the map are near the
edges of the plate. There are also dozens of active volcanoes also near the edges of the plate.
An earthquake occurs when parts of the plates move along a fault. A few centimetres movement along a fault only a
hundred metres long will produce an earthquake of Magnitude 2 or 3. The Magnitude 9.1 “Tsunami earthquake” on
December 26, 2005 had up to 10 metres of movement along a fault line, 1000 km long. Vertical movement of the
seafloor caused the tsunami wave.
– spreading zones between continental plates
Where the continents are pulling apart the oceans are getting wider. The rocks on the sea floor near the mid-ocean ridge
have formed from the volcanic rocks that came out of the undersea volcanoes in the mid-ocean ridge and are young
(only a few million years old). Sea floor rocks closer to the continents are older. The oldest sea floor is the northwest
Pacific Ocean floor, which is less than 200 million years old; some parts of northwest WA are over 2000 million years
old.
– fossils in common on Gondwanan continents, including Glossopteris and Gangamopteris flora, and marsupials
When Gondwana existed as a single landmass about 100mya many of the plant and animal species spread over the
whole area. Most of these early species have since become extinct but fossil remains have been found on some of the
Gondwana continents. Two such plant species are Glossopteris and Gangamopteris; early fern-like trees. Fossils of
these plants have been found in Australia, India, Africa and South America.
Living marsupials are in Australia and South America and fossils have been found in Antarctica. Africa split away from
Gondwana before the early Marsupials reached there.
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– similarities between present day organisms on Gondwanan continents
Living marsupials are in Australia and South America and there are also opossums in North America. The Gondwanan
Continents have large flightless birds such as emus, ostriches, rheas and the now extinct moas of New Zealand. Similar
plant groups, Proteaceae (Protea flowers of South Africa are almost the same shape as the NSW Waratah but smaller
and without the brilliant red colour) and Myrtaceae (= the plant group that includes gum trees; but you will call gum
trees Eucalypts) are on these continents.
The NSW Waratah, Telopia speciosissima. This is the species found around Sydney.
More of my Waratahs. . These are on a bush that is a hybrid between two of the four species of waratah in Australia.
Each bloom is made up of many small flowers working together to produce more nectar and more colour to attract birds
and insects to crosspollinate them. The Proteas from South Africa are in the same family as the Waratahs.
It was the similar plant and animal groups on the southern continents that led Biologists to accept the Theory of
Continental Drift before the Geologists.
David Dobeson
2005
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discuss current research into the evolutionary relationships between extinct species, including megafauna
and extant (= not extinct = alive today = not extinct yet Mr D) Australian species
Because Australia has been isolated for about 40 million years divergent (= genetically similar animals that have
evolved to look different) evolution has allowed the few early types of marsupial to evolve into hundreds of different
types in nearly every possible ecological niche (= ecological place and role); large grazing herbivores ( giant wombats
and giant kangaroos ), tree climbers ( koalas and possums ), carnivores (marsupial lions and Tasmanian Marsupial
Tiger).
The modern Australian native organisms are the remains of a much wider range that existed up to about 20, 000 years
ago. Giant wombats, giant kangaroos and giant emus are often called “megafauna” (= huge animals). The megafauna,
were probably hunted to extinction by aborigines and their dingoes. Their habitats were probably also altered by
hunting fires set by the aborigines. Dingoes were brought to Australia about 5000 years ago, as camp dogs by
aborigines. They are sometimes called “native dogs” but they are placentals like all other dogs and have no connection
to our marsupial native animals. Since whites arrived only 200 years ago the clearing of some ecosystems has
dramatically further changed the food and shelter available to many species leading to their extinction eg Tasmanian
Marsupial Tiger.
This photo is of real bones of a cow sized, giant wombat or Diprotodon (the one on the right) that died probably only
10,000 years ago near Coonabarabran in northern NSW. Note the molars for grinding plant material and the lack of
canines. The specimen is in the Tourist Centre in the town.
The southern continents have pine trees, but not with thin needles like the pines and firs of the northern hemisphere.
Our Gondwana origin pines have thick dark green needles or leaves. The best known example is the Norfolk Island pine
that stands behind nearly every NSW beach; a perfectly symmetrical tall cone shaped tree (it looks like a very cheap
plastic Christmas tree) with long flexible branches, spiked with hundreds of short sharp leaves; great for whipping the
legs of your friends. Monkey puzzle trees in South America, New Caledonian Pines on a few islands in the Pacific,
Bunya Pines from QLD and hoop pines from New Guinea and Queensland are all in the same genus Araucaria. The
Wollomi Pine, often called the fossil tree or dinosaur tree has been in the news since it was “discovered” in 1994. It is in
the same family as the Auricarias.
A well secured Wollemi Pine, Wollemia nobilis, at Royal Botanical Garden in Sydney. Two small stands of 100 trees
were discovered, in 1994, by David Noble in Wollemi National Park, about 200km northwest of Sydney. The first crop
of offspring were auctioned in October 2005, some for more than $10 000 each. The stands show very little genetic
variation and might propagate asexually. This is a major worry if diseases or fires occur in the area. Only a few people
know exactly where the stand of trees is and they are decontaminated before and after each visit to try to reduce the risk
of introducing diseases, particularly fungal diseases. Unfortunately there have been reports that such diseases, might
have already been spread to the area, by unauthorized visitors.
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Until its discovery the Wollemi Pine was only known from fossils many millions of years old.
Pictures of a fossil of a leaf of a Wollemi Pine is available at http://www.wollemipine.com/ .Marketing seems to be part
of all modern science; at Wollemi.com you could even register for the Sotherby’s auction
A New Caledonian Pine, Araucaria columnaris. These were used in the background of some of the scenes of “Walking
with Dinosaurs” because the Pacific islands where they grow, have few flowering trees and grasses. Conifers and ferns
were the dominant plants during the time of the dinosaurs.
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A young Hoop Pine; Araucaria cunninghamii from New Guinea and Queensland. It can grow to more than 40 metres.
A Hoop pine (left), a Bunya pine (right) and a Norfolk Island Pine (on the next page) are all members of the Araucaria
genus. This Hoop Pine in Mt Kuringai looks very “ratty” at the top, as do many of the larger specimens in parks around
Sydney. Older Bunya Pines develop a very characteristic dome shape on top that can be recognized from kilometers
away. Many were planted in parks, schools and large gardens in the 1800s. They are now 30 metres high and produce
pine cones that look like enormous pineapples and weigh up to 10 kg. The threat has meant that many in schools Bunya
Pines have been cut down.
David Dobeson
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In ALL HSC subjects you are expected to answer questions that will be asked using a common set of key
words. The list of key words is available from the Board of Studies at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/glossary_keywords.html.
Make sure that you have the list on your notice board at home, know what each term means and be able to
answer questions using them. The higher skills; analyse, assess, evaluate, investigate and synthesise, are
expected to be handled by the Band 5 and Band 6 students. Your answers could include maps, diagrams or
tables. Assume that each question is worth 5 marks. Earn AT LEAST 5 marks for each question.
Distinguish between convergent evolution and divergent evolution
Compare placentals, marsupials and monotremes. (Check to BOS meaning of compare)
Propose a reason to explain the distribution of ratite birds on earth.
What distinguishes a Tasmanian Tiger from a Bengal Tiger?
Archeopteryx probably could not fly. Propose three possible reasons that it had feathers if they were not for
flying.
David Dobeson
2005
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Students:
•
solve problems to identify the positions of mid-ocean ridges and spreading zones that infer a moving
Australian continent
http://kartoweb.itc.nl/gondwana/gondwana_gif.html
David Dobeson
2005
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identify data sources, gather, process and analyse information from secondary sources and use available
evidence to illustrate the changing ideas of scientists in the last 200 years about individual species such as the
platypus as new information and technologies became available
David Dobeson
2005