Download How Australia was formed – Geographical

Introduction
Australia is often referred to as an ancient land, the oldest of continents. Australia
has not always had its present shape or position on the globe. Even today, it is in the
process of colliding with South-East Asia. Originally, Australia was joined to a supercontinent, referred to as Pangaea (meaning 'all lands' in Greek), before it separated
and drifted across the Earth's surface, experiencing a variety of different climatic
changes and geological events. In focusing on Australia's journey across the Earth, it
is possible to gain a greater insight into the evolution of Australian landforms, soils,
flora and fauna. See image 1
Origins of plate tectonic theory
Plate tectonics is a geological theory used to explain the phenomenon of
continental drift, which is the tendency of landmasses to move around the Earth.
This theory provides an explanation of how Pangaea was able to break up into two
separate landmasses, Gondwanaland and Laurasia, which in turn broke into the
seven continents that exist today. See image 2
After Pangaea split into two landmasses, Australia was located on the southern
super-continent of Gondwanaland. Other present-day continents which formed part
of Gondwanaland are Africa, Antarctica, South America and some southern parts of
the Asian continent.
The existence of Gondwanaland was first discovered during the late 19th century by
an Austrian geologist named Eduard Suess. Suess named the ancient landmass
after a province in Central India called Gondwana. This was after he discovered that
a plant species found in Gondwana matched the fossilised remains of plants found
on other continents in the southern hemisphere. Suess' findings helped to form the
theory of plate tectonics.
What is plate tectonics?
The Earth is made up of many layers. From the outside in, they are the crust, the
mantle, the outer core and the inner core. Central to the theory of tectonic plates is
the idea that the outermost part of the Earth, the crust, is composed of two layers:
the lithosphere and the asthenosphere. The lithosphere is composed of the crust and
the solidified uppermost part of the mantle. The asthenosphere lies underneath the
lithosphere, and is made up of the inner viscous part of the mantle. The lithosphere
is a more fixed, rigid, cooler substance than the hotter, mechanically weaker
asthenosphere. See image 3
The plate tectonic theory hinges upon the principle that the lithosphere exists as
separate, distinct tectonic plates, which float on the fluid-like asthenosphere.
Volcanic activity, earthquakes, mountain building and oceanic trench formation occur
at the plate boundaries, which are the areas separating the plates. The tectonic
plates can be categorised as continental plates or oceanic plates. See image 4
The Australian continent is located on the Indo-Australian Plate, which includes the
surrounding Indian Ocean and the Indian subcontinent. The Indo-Australian Plate is
subdivided into two plates along a low active boundary: the Australian Plate and the
Indian Plate. The Indo-Australian plate was originally connected to Gondwanaland,
and later Antarctica, before it began to drift north some 96 million years ago. As the
continent moved northwards, the climate became drier. As the Australian continent
drifted north it developed unique flora and fauna.
The Australian Plate is drifting 35 degrees east of north at a speed of 67 millimetres
a year. The easterly side of the Indo-Australian Plate is a convergent boundary with
the subducting Pacific Plate. From the fusing of these two plates, whereby the
Pacific Plate slides underneath the Australian Plate, the Kermedac Trench is formed.
New Zealand is located at the south-eastern boundary of the plate and was part of
Australia before detaching around 85 million years ago.
An old, flat continent
Australia has been described as old and flat. This is because the Australian
continent has experienced a long period of geological stability, which means there
has not been much volcanic or tectonic activity in the recent past. As a result,
Australia has been open to the forces of weathering and erosion, which are
processes that break apart and move rocks and soil around. In the distant past,
however, there were volcanic eruptions and earthquakes that helped shape the face
of Australia. See image 5