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Evidence From Gondwana

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Shaleen Singh

on 14 August 2014

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Transcript of Evidence From Gondwana

Plate Tectonics And Development Of Gondwana
Alfred Wegener { a German meteorologist, 1912 } proposed that
[ plate tectonics ] was the isolating mechanism that led to the formation of continents that we have today. So once the world was a big land mass { called
, 250mya } that broke up forming continents. He said that about 150 mya Pangea split up into two pieces-
[ now North America, Greenland, Europe and Asia ] in the northern hemisphere and
[ now South America, Africa, Australia, Papua New Guinea, New Zealand , Antarctica and Madagascar as well as the Indian subcontinent ] in the southern hemisphere.
Evidence for the theory of continental drift:
Fossils of plants such as
provide further evidence that Australa was once a part of Gondwana. These fossils are found in
Southern hemis phere co ntinents [Australia, Antar ctica, Afri ca, South America, New Zealand, Madagascar and the Indian subconti nent
. The rocks containing these fossils are all dated at the same ages provides an extra proof for the existence of Gondwana.
Through this assignment, we will learn about:
Evidence that supports the assertion that Australia was once part of a landmass called Gondwana.
Matching continental margins.
Position of mid-ocean ridges.
Spreading Zones Between continental plates.
Fossils in common on Gondwanan continents, including Glossopteris and Gangamopteris flora and marsupials.
Similarities between present day organisms on Gondwanan continents.

Evidence From Gondwana
Geological studies show that the Earth's crust is made up of plates that float and move on top of the mantle [molten rock]. When these crustal plates collide, mountain ranges are formed or earthquakes occur. Due to pulling and pushing of plates cause them to separate or collide so that ridges form at the edge of the two plates. So in conclusion we can say that the plates on the Earth's crust are constantly moving as are the continents on them to explain the formation of the world's continents, mountains and mid-ocean ridges.

Did you know that each year Australia moves 7cm northwards? In 50 years time your bedroom could effectively be across your street.
When we study a map of this world it appears that Africa and South America could fit together as in a jigsaw puzzle. Scientists have used this as an evidence for continental drift and for Australia once being part of Gondwana.
In 1960s, scientists noticed that a line of
was formed globally on the oceans' floors. They also discovered that the youngest rocks were near these ridges and the oldest ones were further away. This indicates that the ocean floor is moving and spreading apart. The presence of mid-ocean ridges is now accepted as further proof that continents can move and that Australia was once part of Gondwana.
(Evolution Of Australian Biota)
For years scientists tried to explain why Australia's Biota is so different. Some thought that the Earth's geography played a major role and this was later supported by studies in geology and palaeontology [ study of fossils ]. So as a result all the continents were a result of isolating mechanism which will be further described till the evidence fom Gondwana in this assignment
Wegner thought that because the continents today could fit together like a jigsaw puzzle this was evidence for the process of continental drift. He noticed the similarities in the shoreline of continent on both sides of the Atlantic Ocean. He started fitting them together. Particularly, he liked the way in which SOUTH AMERICA and AFRICA fit.
In 1960s, scientists proposed a new map using the edges and shorelines of different continents and fitted all of them together as the true boundaries of the continents.
Fossi evidence supports this theory as rocks layers found in different continents that are far apart match. For e.g: the fossil records suggest that marsupials were originally North American and rock layers on the edge of Antarctica match up with those in southern Australia, scratch marks formed by glaciers on rocks in Antarctica matched up with glacial marks on rocks in Southern Australia and similar rock formations were found in cliffs in Tasmania and in Antarctica.

When the crustal plates moved, continents separated and travelled away from eachother, taking the resident flora and fauna with it. These flora and fauna had common ancestors but developed differently due o isolation. However, patterns of distribution of closely related species can be traced by fossil records. For e.g. Australia has the greatest diversity of marsupials but they probably evolved first in North America and then travelled towards South America and across Antarctica to Australia by land bridges. When these continents were separated [ Australia became a separate continent 40 mya ] the marsupials population evolved, multiplied and adapted in Australia according to the environmental pressure on them. Australia now has a rich and diversified population.
Matching Continental Margins
Mid-Ocean Ridges
Wegener used documented cases of fossil organisms that had been found on different landmasses that could not have crossed the current oceans. Fossils of mesosaurus have been found only in South America and Africa. Remains of other organisms appear to link these two continents.
What Could Have Happened?
Fossil record shows that marsupials once lived on all continents of Gondwana, today there are a very few countries with living marsupials. Some of the marsupials from North America may have travelled to South America and later to Australia via Antarctica.
Australia now has many diverse marsupials
such as
Kangaroos, wombats, Tasmanian devils, bandicoots and possums
occupying many habitats. Only
marsupials presently living in North and South America are opossums.

South America has 1/3 of the world's marsupials
. In
Papua New Guinea
there are many
marsupials such as gliders, possums and tree kangaroos
. Again this is an Evidence that supports Gondwana.
Similarities Between Existing Biota And Gondwanan Continents
Existing Biota
Existing species provides evidence to Gondwanan ancestry. For e.g. Primitive Evergreen Trees called

Nothofagus moorei
are found in
Lamington National Park in Southern Queensland
and in Barrington Top, NSW as well as in southern Australia and in Papua New Guinea, New Zealand, New Caledonia and South America.
Fossil Leaves, wood and pollen

have also been
found in Antarctica.
Other fossils such as
[only found outside Australia in South America and New Zealand],
Callistemom, Melaleuca
etc. are only found in the southern hemisphere.

Living Fauna - Flightless Birds
The pattern of distribution of
ratites (flightless birds)
and how closely they are related also points towards the existence of Gondwana.
Emu & Cassowary - Australia
Ostrich - Africa
Rhea - South America
Kiwi - New Zealand
Cassowary - Papua New Guinea

DNA analysis shows that these birds have similar DNA indicating a common
The emu is more closely related to the cassowary of north Queenland and Papua New Guinea but most distantly related to the rhea and ostrich.

Existing Fauna
is an example of fauna found in the
southern continents ( Australia, Africa and South America )
Only 6 species.
Lungfish are primitive fish that have remained relatively unchanged from the original species called
living fossils.

These require shallow, slow-moving, heavily vegetated creeks for spawning and nursery habitats
. They can survive (moist) for several days out of water but will not survive in total water depletion.
They are only found in Queensland in thde Mary and Burnett River,
waterways such as Enoggera Creek (introduced). A large Dam has been just completed on Burnett River for water consumption and the govt. is planning to Dam the Mary River Too.
Plate Tectonics
Development of Gondwana
Song on Continental Drift
nsw biology
Carolyn.J, Pauline.R and MEA 2007
Google Images
Youtube Videos

Refer to this video for further information of Evidence for Gondwana
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