Anaspides.net

Australia Before Time

 

 

An Envelope of Time 

Scientists divide the history of the Earth into time periods, to represent how it has changed over billions of years.

The time scale shows the time periods (see right), starting with the Archaean period 4560 million years ago and ending in the Quaternary period.  Click to view geologic timeline (.pdf high definition).)

The Australian landscape has rocks that come from each of these time periods, including special rock 'windows' that tell us about the geological age of the planet, and the origins of life.

Some of these special geological places are cave systems, landscape formations and mountains that can be visited and explored, like Chillagoe Limstone Karst Area, Queensland; Wolfe Creek Crater, Western Australia; Gosses Bluff, Northern Territory; and Blue Lake, New South Wales. Others contain rare and very fragile fossils, like the Ediacara fossils from South Australia that can be seen in museums.

The timeline is an expandable and adaptable diagram.  Eons represent the longest span of time followed by Eras, Periods and Epochs.  Epochs can be divided further into zones and stages, or other units suitable to a particular field of study.  For instance, palaeontologists frequently add a faunal and biostratigraphic zone to the diagram. A Long Long Time Ago, In The Beginning, There Was........ 

The Earth was formed around 4.5 billion years ago from molten rock. As the Earth cooled, mineral crystals formed. Some of the oldest rocks in the world have been found in Australia, and are around 3.7 billion years old, from the Murchison region in Western Australia. These ancient rocks contain tiny crystals that are even older, dating from 4.4 billion years ago, close to the time of the Earth's own formation.

At this time the atmosphere was a lethal mix of methane, nitrogen and carbon dioxide. From old north-western rocks dating to about 3.5 billion years (during the Archaean period) come stromatolites that provide the first signs of life on the planet. They were formed by blue-green algae which dominated life on earth for a billion years, and exerted a permanent effect over their environment by excreting a new gas: oxygen, which helped to form the atmosphere needed to sustain today's complex life-forms.

LEFT: Stromatolite from South Australia (Photo - Iain Williams). 

 

ABOVE RIGHT: Banded iron formation, Pilbara WA. The rock bands are the result of iron being rusted by oxygen in the Earth's atmosphere 3.3 billion years ago
(image courtesy of Sarah Belfield)


 

 

Beneath the Sea in an Octopuses Garden

Today Australia is a hot, dry continent but hundreds of millions of years ago the landscape was very different.Between 600 and 550 million years ago (during the Precambrian period) most of eastern Australia lay under warm tropical seas, inhabited by soft bodied organisms, similar to jellyfish. Some of these organisms became trapped in the fine silt at the bottom of the seas and were fossilised as the silt turned to stone. As sea levels changed, the seabed become part of what we now know as the Flinders Ranges.

The discovery of what are now known as the Ediacara fossils in 1946 was extremely important, as it was the first time the fossilised remains of a community of soft-bodied creatures had been found in such old rocks anywhere in the world. These fossils are on display in the South Australian Museum.

LEFT: Ediacara fossils (AHC collection)

Strange fish also swam in the sea that covered the north-west of Western Australia more than 350 million years ago. Armour-plated fish (Placoderms) first appeared 420 million years ago and dominated the seas and rivers of the Devonian period. These included some of the most bizarre fish ever found such as the antiarchs that had external bone-covered arms. The world's best-preserved placoderm fossils come from Australia and the Gogo fossils are among the Most impressive.

LEFT: Gogo fish fossil, displayed at the Western Australian Museum
(AHC collection).  Gogo refers to the location the fossils were first discovered

Other parts of Australia were also covered by shallow seas. Chillagoe Limstone Karst Area in Queensland is the remains of an ancient coral reef that formed around 380 million years ago (in the Devonian period). As sea levels dropped, the reef was exposed, and formed a towering landscape of limestone (known as karst landscape), probably rising to more than 70 metres high in some areas. Over hundreds of millions of years many of the high ridges were gradually moulded into towers by wind and water.

LEFT: Chillagoe-Mungana Caves National Park
(image copyright DW Stock library)

Beneath the peaks and ridges are more than 50 caves, some of which can be visited and explored. The caves are home to many species of life, including 17 species of bats. Fossils of extinct crustaceans, evidence of the area's marine origins, are also found in some caves.


In The Footsteps of Dinosaurs

Much later came the era of dinosaurs in Australia, during the Triassic, Jurassic and Cretaceous periods of our history (240 million to 65 million years ago).
Lark Quarry near Winton, Queensland records a unique snapshot from approximately 100 million years ago, when a large, carnivorous tyrannosaur-like dinosaur trapped a mixed herd of smaller two-legged bird-like dinosaurs, possibly Coelurosaurs and Ornithosaurs, causing a stampede.

Lark Quarry is one of the best-preserved sets of dinosaur footprints in the world. More than 3 300 footprints of 150 individual dinosaurs can be seen today in the rock that lies within the visitors' centre.

The Cretaceous in Queensland (new dinosaur discovery)

The Cretaceous age (145 to 65 Million years ago) was a time of great global change, culminating in the extinction of the dinosaurs. For Queensland the most important slice of this time was between 130 and 95 Million years ago when much of the sediment which filled the Great Artesian Basin was deposited.

Elliot (pseudo name for the discovered dinosaur which belongs to  Titanosaurid group of Sauropods - the largest of a group of plant eating dinosaurs) lived from a period of time called the Cretaceous, about 95 million years ago. The eastern coastal highlands were then dominated by a large, violent, active volcanic region, now only preserved in the rocks of the Whitsunday Islands. From this region came the great volumes of sediment which now form the Cretaceous rocks of the Great Artesian Basin. 

The sea flooded the centre of the continent at least four times during this period, but it is the rocks formed during the period 110-95 Million years ago that contain the majority of Australian Dinosaur remains.

At this time the continent was much further south than at present, with Queensland straddling 55°S. The climate was temperate, a fact borne out by strong seasonality in the growth rings of fossil wood.
The new dinosaur discovery comes from the last flooding, 98-95 Million years ago, which deposited sediment from rivers, lakes and streams on a vast flat plain stretching from the eastern highlands to the Boulia district. The sediment is now known as the Winton Formation 

Though the climate was cool, the vegetation was relatively lush. On the plains were great open temperate forests of conifers, ferns, ginkgoes and cycads, — and the first shrub-like flowering plants. These are known from the many fossil plants found in the Winton Formation.

Another area that gives us an insight into dinosaur habitats is Dinosaur Cove, Victoria. During the early Cretaceous period, Australia was far to the south of its present position and joined to Antarctica. Fossil sites at Dinosaur Cove and Flat Rocks on the southern Victorian coast tell us much about dinosaurs in this harsh polar ecosystem. One example was Qantassaurus intrepidus, a small two-legged dinosaur with long hind limbs and short forelimbs, about the size of a turkey, which ate plants and insects.

LEFT: Dinosaur footsteps frozen in time at Lark Quarry, QLD (image courtesy of Tourism Queensland)

Many of the creatures from Dinosaur Cove were "living fossils" when alive - that is living in Australia in a time when they are known to have already become extinct elsewhere in the world. Others are among the earliest known examples of their type anywhere in the world.



Intrusion from the Stars

Changes to the world's terrain came from many natural causes, such as erupting volcanoes and earthquakes. Outer-space played a part, as meteorites and asteroids pounded to Earth, causing massive upheavals in the terrain.

Australia has some of the best examples of meteorite impact sites anywhere in the world - places like the isolated Gosses Bluff, west of Alice Springs. This site was created 142 million years ago (during the Jurassic period) by a 600 metre wide meteorite, smashing into the Earth with a force one million times greater that of the Hiroshima atomic bomb explosion.

The meteorite penetrated more than 5 000 meters into the ground, probably vaporising on impact and forming a crater about 22 kilometres across. 

LEFT: Gosses Bluff, west end of the MacDonnell Ranges, NT (image copyright Steve Strike)

Another meteorite, which plunged to earth 300 000 years ago (during the Pleistocene period), created an almost perfectly circular crater at Wolfe Creek. The crater lies 90 kilometres south of Halls Creek on the edge of the Great Sandy Desert in Western Australia, and its remote location meant it remained unknown to geologists until 1947.

RIGHT: Wolfe Creek (image courtesy of Fugro Spatial Surveys Pty Ltd)

The walls of the crater rise to 35 metres high, and originally the basin would have been much deeper (around 150 metres deep) but is now largely filled with sand. Unusually large trees grow here, drawing on reserves of water which are trapped in sink holes after the summer rains.

Fragments of the meteorite remain as rusty balls of iron-shale littering the crater slopes, making this one of only 18 craters in the world with surviving meteorites.

LEFT: Depiction of the meteorite impact that created a 900 m wide crater in Wolfe Creek (image courtesy of Western Australia Museum)Glaciation, Megafauna and Climate Change
About 38 million years ago, Australia separated from Antarctica and Tasmania was connected to the mainland by a low plain.

The Continent Cools and Dries

The continent was becoming drier and colder, causing changes to the wet rainforests that had dominated for millions of years. In Tasmania, a rare fossil site from this period contains exquisitely preserved details from a rich variety of plants. The site shows that Tasmania was still covered by moist forest, dominated by Southern Beech, a group of trees that today in Australia can only be found in Tasmania and in isolated remnants along the Great Dividing Range, but in the Miocene period (24 million to 5 million years ago) covered most of the continent.

During the Pleistocene (1.8 million to 10 000 years ago), the world underwent a series of ice ages and sea levels rose and fell. The rocks in the cliff face along the well traveled tourist track of the Port Campbell coast in Victoria record this movement of sea levels.

RIGHT: Port Campbell Coast, Victoria (image copyright Jiri Lochman)

Port Campbell National Park stretches along beside the Great Ocean Road in southern Victoria for 50 kilometres. It is one of the most spectacular and unusual coastlines in Australia, with outstanding examples of wave-cut landforms such as arches, rock stacks, blowholes, caves and coastal gorges. During their evolution, the cliffs, which are up to 70 metres high, have been raised above sea level, cut by rivers, and shaped by the constant pounding of the waves generated from the Southern Ocean.

Megafauna

It was during this period that many of the Australian fauna evolved to gigantic proportions to become known as the megafauna.  Megafauna inhabited all of Australia and apex predators were reptiles rather mammals as in other parts of the world.  Megalania prisca was a giant varanid lizard that exceeded 5 meters in length, Wonambi naracoortensis was a snake belonging to the python family that grew to 10 meters.  Other mammals that lived at this time include giant wombats, koalas, kangaroos, devils and cow-like diprodonts; many of these animals are extant and smaller in size.  The Thylacine (Tasmanian tiger) belongs to the megafauna family and only became extinct in 1947, despite repeated sightings from Tasmania.

During the last Ice Age, glaciers formed in Tasmania and the Australian Alps. Glacial processes at this time made a major contribution to the present day character of this region, creating glacial lakes, like Blue Lake. Today these alpine lakes are the only wetlands on the Australian mainland which are covered by an ice sheet throughout the winter months.

LEFT: Blue Lake, Kosciuszko National Park (image copyright Mike Edmondson)



Secrets Still Await Discovery in Australia's Remote Regions

In such an ancient land as Australia it's hard to imagine that there are any surprises left to discover. But there are still many secrets to find.

One spectacular area that remained a virtual secret to the outside world until 1972 is the Undara Volcanic National Park, Queensland. The Undara Lava Tubes, dating from the Pleistocene period about 190 000 years ago, are the world's longest and best preserved lava flow from a single volcano.

Undara was a shield volcano that erupted 190 000 years ago. Lava flowed more than 90 kilometres to the north and over 160 kilometres to the north-west, at a rate that would have filled Sydney Harbour in six days.

LEFT: Visitors can tour the magnificent Undara Lava Tubes, north Queensland (image courtesy of Tourism Queensland)

The hollow tubes formed when a river of lava began to cool around the edges. The front edge of the flow gave way, allowing the lava to drain away and leaving a tube.

 

 


References

Adapted from website of Australian Heritage Commission (all rights reserved - for private study only).

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