GEODIVERSITY

Gondwana
The great supercontinent

Parks and Wildlife Service Tasmania
DEPARTMENT of TOURISM, PARKSHERITAGE and the ARTSThe Earth’s surface does not consist of a motionlesscrust but rather of large crustal plates which move andjostle against each other. There are seven large plates
and many smaller plates (100 to 150 km thick) thatdrift around the Earth’s surface, highlighted in the
diagram below.

Their distribution is very difficult to explain unless all
the continents were linked together. There is also aremarkable jigsaw puzzle fit between many of thesouthern continents which Wegener noticed and so
proposed the then radical theory of continental drift.
This theory was discredited for
decades by geologists until the1960s but is now widely
accepted as the theory of plate
tectonics.

Australia in thenorthernhemisphere?

Earth’s crustal platesContinental drift
Continental drift is apparently a result of these crustal
plates being dragged along by movement in deeper
layers of rock in the mantle.
Volcanoes and earthquakes all provide evidence for
the Earth’s wandering continents. The continents
actually move as a consequence of volcanic processes
in oceanic areas known as mid oceanic ridges wherebasalt oozes out onto the sea floor, forcing adjacentplates apart.
Another mechanism driving the movement of the
Earth’s plates are large convection currents in theEarth’s mantle.

It seems quite absurd to suggestthat the land which is now
Australia was once situated in
the northern hemisphere, that acouple of hundred million
years later it was slowly
moving to the south pole, andthat in 20 million years time
the northern tip of Australia
should reach the equator. This
is what continental drift is all about with continents
coalesce and segregatecolliding and diverging.
Supercontinents form and break up over time as thecontinents move.

What was Gondwana?
Gondwana was the great southern landmass thatformed as a result of the division of a much larger
supercontinent known as Pangea about 250 million
years ago. This Gondwanan supercontinent consistedof present day landmasses: Africa, South America,
India, Madagascar, Australia and New Zealand. The
other section of Pangea, known as
Laurasia,comprised what are now Europe, Asia andNorth America.

Did the supercontinents reallyexist?

The Big Rip

Alfred Wegener, a German meteorologist, proposed
the original theory in 1912, after noticing that there
were similar glacial deposits in the southern
continents, which had a rational distribution whenplotted on a geometric reconstruction of thesecontinents known as Gondwana.

The Gondwanan landmass started to disperse about
165 million years ago. The dispersal caused great
tension in the Earth’s crust and volcanic activity
followed as conduits were created in the continental
crust, tapping the molten rocks (magma) in theEarth’s mantle.

The dolerites that outcrop over extensive parts ofcentral and eastern Tasmania, together with similar
igneous rocks in South Africa, South America andAntarctica, are the solidified evidence of the magmafrom the Gondwana break up.
The Australian plate took a very long time to separate
from the Antarctic plate. In fact they were the last of
the major Gondwanan continental plates to split, only
45 million years ago. As a result, Tasmania has more
geological similarities with Antarctica than most ofAustralia.
By this time Tasmania had also taken on its triangularshape and developed many of its valley and mountainsystems, which formed as a result of similar faulting
events which created the Bass Strait.
Australia, with its freight of Gondwanan plants andanimal’s started being dragged northwards about 45
million years ago while the first glaciers were
forming in Antarctica. However it still took until
about 5 million years ago for Antarctica to completely
freeze over. This was the first extensive ice to haveformed in Antarctica since the Permian glaciations
300 million years before, which also affected parts of
the other southern continents.
Continents still on the move?
The Australian plate is moving northwards at about
3cm per year. The Himalayan mountain belt isforming today as a result of India colliding with Asia.

Tasmania’s Gondwanan elements
Plant evidence: Fossil evidence suggests thattemperate rainforest was widespread in Australia,Antarctica, South America and New Zealand around45 million years ago. Such fossils and the surviving
species in Tasmania provide evidence of the ancient
link to Gondwana.
There are a number of examples of fossils with aGondwanan connection, the most recent was thediscovery of fossilised foliage of the giant conifer
Fitzroya tasmanensis near Cradle Mountain. Presently
this tree only grows in Chile, but this discovery
provides excellent evidence for the similarities inforest types across Gondwana. These Gondwanan
forests most likely included King Billy pine, pencil
pine and other Tasmanian gymnosperms.
Flowering plants arrived in Gondwana about 100
million years ago and expanded rapidly across thesupercontinent.

The most successful was the myrtle or southern beech(Nothofagus) which provides arguably the strongest
evidence for the Gondwanan landmass. There areabout 40 living species left today distributed across anumber of land masses- three species in Australia,nine in Chile and Patagonia, five in New Caledonia,
14 in New Guinea and four in New Zealand.
The protea family is another with its origins inGondwana, with relations extending from Australia toSouth Africa and South America.
Animal Evidence: There are numerous examples ofanimals in Tasmania that have their closest relatives
living today in land masses that were once part of theGondwanan supercontinent.
The invertebrates provide the most abundant evidenceof this. Possibly the best known example is themountain shrimp (Anaspides tasmaniae) which isvery similar to Triassic (230 million year old) fossils.
Currently, its closest relatives are found in New
Zealand and South America. The Tasmanian cavespider is considered to be one of the most primitive
spiders in the world, and is the only member of its
family outside Chile.
Another most amazing discovery in recent time wasthe vertebrate and invertebrate marine fauna of thePort Davey/Bathurst Harbour areain the southwest, which arealso considered Gondwana
relics. One of theseanimals, the Port Daveyskate, is unique, as it is
the worlds only brackish
water skate, and its
closest relatives arefound in New Zealandand Patagonia.
Echidna
Platypus and echidnas
evolved from ancient ancestors
which inhabited Gondwana. Close relatives ofmarsupials thrive in South America and fossil
platypus have also been discovered in South America.

Further information
Gondwana map: refer to< www. geology.er.usgs.gov/eastern/plates>

Contact
Biodiversity Conservation Branch: DPIWE
134 Macquarie Street, Hobart, 7000
Phone: (03) 6233 6556, Fax: (03) 6233 3477

FURTHER INFORMATIONHead Office:Phone:

134 Macquarie Street Hobart TAS 7000
1300 135 513

Internet: www.parks.tas.gov.au
January 2006
© State of Tasmania