History & Heritage

Gondwana was the great southern landmass that formed over 250 million years ago. This Gondwanan supercontinent consisted of present day landmasses – Africa, South America, India, Madagascar, Australia and New Zealand.

The Gondwanan landmass started to disperse about 165 million years ago, causing great tension in the Earth’s crust and volcanic activity.

The dolerites that outcrop over extensive parts of central and eastern Tasmania, together with similar igneous rocks in South Africa, South America and Antarctica, are the solidified evidence of the magma from the Gondwana break-up.

Further evidence of Tasmania’s Gondwanan link can be found in ancient fossils and rocks, as well as plants and animal species that survive on the island today.

CAMBRIAN, ORDOVICIAN AND SILURIAN PERIODS:
570 - 410 million years ago: the first vertebrates, first land plants with atmospheric oxygen level 10 per cent, first animal life on land and first true fish.

Hundreds of million-year-old sandstone, slate, quartzite and limestone specimens are evident in western Tasmania today.

Between Queenstown and Macquarie Harbour is a tangled mass of mountains rising to more than 900 metres (3,000 feet). Many are residuals of hard Silurian rocks, with steep peaks capped with white quartzite.

Peaks such as Mount Roland and St Valentines Peak in the north-west are Ordovician conglomerates. Other Ordovician peaks have been named after famous geologists and zoologists: Murchison, Lyell, Owen, Jukes and Darwin.

DEVONIAN AND PERMIAN PERIODS:
410 - 235 million years ago: the first seed ferns, amphibians, insects, reptiles, conifers and last trilobites.

What is now western Tasmania emerged from the sea in the Devonian Period, about 380 million years ago. Further west, what is now the sea was still land during the Permian Period 250 million years ago, when Tasmania and Antarctica were all part of Gondwana.

A link with the Permian Period is found in the glacial lakes of the Franklin-Gordon Wild Rivers National Park. Small, rare, primitive crustaceans, Anaspides (sometimes called shrimps), still live there and are also found as fossils in the Permian rocks of Europe.

TRIASSIC AND JURASSIC PERIODS:
235 - 135 million years ago: large scale animal extinction, first dinosaurs, mammals, flying animals and grasses

While western Tasmania features rocks belonging to the very early geological periods, in the centre of the island and in the east they are much younger as a result of geological events in the Triassic (200 million years ago) and following periods.

In the middle of the Jurassic Period, about 165 million years ago, Tasmania was heaved upwards. Molten rock (magma) was forced up though the earth’s crust from depths of 20 kilometres or more, and was intruded sideways for great distances between the planes of sandstone. The magma then cooled and solidified to become the coarse, dark rock known as dolerite. This event marked the start of the break-up of the Gondwana supercontinent.

Dolerite in columnar form can be seen on Ben Lomond and Mount Wellington. Columns of dolerite rock also form the rugged cliffs of Bruny Island. 

TERTIARY PERIOD:
65 - 2 million years ago: Gondwana land splits, primates, the evolution of modern flora, decline of mega-mammals and the first modern mammals.

After the dolerite intrusions there was little geological activity for 70 or 80 million years. At that time Tasmania was still part of mainland Australia. Then, in the Tertiary Period, the rift valley that is now Bass Strait subsided and Tasmania became an island for the first time. Later, during the Pleistocene Epoch, the sea level fell, due to water being stored in huge ice sheets in the polar regions, two or three times, each time rejoining Tasmania to the mainland. As the ice-sheets retreated during the interglacial periods, Bass Strait was flooded again.

During the Tertiary Period, Tasmania was raised to become a tableland about 1,500 metres (5,000 feet) high and sloping to the south.

PLEISTOCENE EPOCH – THE ICE AGE:
2 million years ago - 10,000 years ago: The rise of modern man.

During the Pleistocene Epoch, or Ice Age, the sea fell and rose, shaping mainland Australia. But in Tasmania it was the glaciers that changed the shape of the island, which was buried under ice. Only the highest peaks protruded.

Towards the end of the Pleistocene, the larger ice masses retreated and smaller cirque glaciers formed. As the glaciers slid down the mountains, they gouged out cirques – valleys shaped like amphitheatres. The tops of the mountains were left bow-shaped, with jagged rims and the inside of the cirques are often terraced where harder rocks resisted the glaciers.

There is a perfect example of glacial topography at the foot of Cradle Mountain. From the west the mountain appears as a jagged arc of columnar dolerite, with many single columns standing isolated. From the same point Barn Bluff can be seen to the south, also columnar dolerite but apparently untouched by glacial action. At the base of Cradle Mountain, the ground dips to a deep gorge and two great glaciers can be seen – Crater Lake and Dove Lake.

Our glacial heritage

Tasmanian topography has changed little since the end of the Pleistocene Epoch. Wind, weather and water continue to erode the landscape, but the effect is hardly visible. In the flat-bottomed valleys excavated by the ice, swampy plains are covered with button grass, which is slowly turning into peat. Frost splinters the mountaintops, rivers cut into the valleys and the sea wears the coast but these processes are slow.