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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 super-continent, 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


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