Download Gondwana The Earth is really an ocean planet since less than one

NATURE NOTES
Gondwana
The Earth is really an ocean planet since less than one third of the Earth’s
surface is covered by land and over two thirds covered by water. The land
mass consists of continents and islands which are grouped together into
seven regions - North America, South America, Asia, Africa, Antarctica,
Europe and Australia/Oceana.
According to the Pangaea theory, millions of years ago all the land mass on
Earth consisted of one super continent called Pangaea (meaning “all lands”
in Greek). In the Jurassic Period (208-144 million years ago) Pangaea began
to stretch and rift, ultimately breaking into two huge continents separated by
the Tethys Sea. The northern continent was called Laurasia and the southern
continent was called Gondwana.
Laurasia eventually split into Eurasia and North America.
Gondwana eventually split into Antarctica, Africa, Arabian Peninsula,
Madagascar, Australia, New Zealand, South America and the Indian
subcontinent.
In our region New Zealand separated from Australia 80 million years ago,
Australia and Tasmania split from Antarctica 45 million years ago. As it
moved towards the South Pole Antarctica grew colder, glaciers appeared and
the flora and fauna succumbed to the cold leaving only fossils as evidence
that dinosaurs, tree ferns, marsupials and forests once occupied Antarctica.
When Alfred Wegener, a German natural scientist, first presented his
hypothesis of Pangaea and drifting continents, he indicated as proof - the
jigsaw fit of continental coastlines; fossil distribution indicating identical
species in same layer sequence in continents that are now separated;
geological evidence such as a chain of mountains in West Antarctica which
are an extension of the Andes. Wegener’s work was contrary to accepted
views at the time, which regarded continents as fixed. Evidence obtained by
oceanographic studies in 1950s and 1960s vindicated Wegener’s
fundamental conclusion that modern continents are fragments of Pangaea
The influence of the continental split on living species can be seen in nearby
Lamington. The plant family of Nothofagus includes Southern beech forests
which evolved in Gondwana. When the super continent split apart the
ancient trees were carried with them. This explains why Nothofagus forests
are only found in South America, New Zealand, Australia, New Guinea and
New Caledonia and why fossilised pollen grains of Nothofagus were found
in Antarctica. A walk through parts of Lamington National Park gives an
insight into the appearance of the ancient Gondwanan forest that once
covered Australia. The Antarctic beech (N. moorei) and other relic species
from Gondwana such as southern conifers (Podocarpus and Araucaria),
Ginkoites (primitive seed-bearing trees), cycads and giant horsetails, ferns,
seed ferns (e.g. Dicroidium) and club moss are survivors from the super
continent.
Wegener’s hypothesis that continents drifted was a precursor of modern
plate tectonics.
The continental and oceanic crusts of tectonic plates are rigid but float on the
hotter, viscous layer of the Earth’s mantle. Heat, subduction and the creation
of new crust drives continuous continental movement. It is estimated that
Australia is moving north at the rate of 10mm per annum.
Nadia O’Carroll