Recreating the Country blog
H G Well’s classic story ‘The Time Machine’ explores the idea of time travel through the adventures of an English gentleman who invents a time machine that carries him to past and future worlds. Like the time traveller’s machine the sciences of geology and paleontology provide windows into past worlds through fragments of evidence found in ancient rocks
There is a lot of ancient history hidden in the rocks of the Barrabool Hills and this history has played an important part in developing its unique landscape and vegetation. Let’s imagine we have borrowed the amazing time machine and it has carried us through many millennia in a matter of seconds to a time 135 million years ago when it all began.
We’ve arrived and we’re mystified because we’re sitting in total darkness and the air is sharp and cold. We zip up our windcheaters and pull our beanies down over our ears to keep out the chill of a deep arctic winter in Gondwanaland.
We shine our torches into the eerie darkness and see snow under the ghostly silhouettes of trees hugging the edge of a shadowy frozen lake. A dog sized animal ambles past sniffing the air curiously, its paw prints in the snow are strangely reptilian.
135 million years (Ma) ago Gondwanaland was a super continent made up of Australia, Antarctica, Africa, New Zealand and South America and it was sitting around the South Pole. Australia was so far south on planet earth that it experienced perpetual summers and perpetual winters lasting up to six months of the year, much like Norway, Alaska and the north of Finland experience today.
We touch the accelerator on our time machine and travel back another six months to the perpetual summer where the sun peaks through a cloudy sky. It feels like a crisp warm spring day in modern Australia though the vegetation seems to be a more vivid green.
A large platypus scrambles onto the bank and startled by our time machine turns and slides back into the lake. The presence of the platypus and the sight of a small polar dinosaur drinking at the lake’s edge confirm that the lake is freshwater. We notice that the dinosaur has large possum-like eyes for night vision in the arctic winter and a long tail reminiscent of a kangaroo. Its ability to hunt during the long winters suggest that it is warm blooded like the ancient platypus.
We can now appreciate that the lake extends as far as the eye can see and is surrounded by a lush vegetation of ferns, cycads, clubmosses and horsetails, creating the understorey for a towering conifer rainforest related to the Wollemi Pine (family Araucariaceae), complemented by Myrtle Beech, Nothofagus cunninghamii and Gingko trees.
Note 1 - Gingkos & Note 2 - Plant fossils>
The first flowering plants including the ancestors of the Banksia, Grevillea and Macadamia (Proteaceae family) are beginning to bloom in this prehistoric world but there are no familiar trees like the acacia, eucalypt and casuarina.
This temperate humid climate has produced a lush rainforest nourished by numerous rivers and streams. It is the time of reptiles and dinosaurs and the ‘birdsong’ of the flying dinosaurs (pterosaurs) is likely to have sounded like the rasping shriek of the White-faced Herons that frequent our present day wetlands. This unnerving sound echoing around the humid misty forest gives this place a pungent and menacing atmosphere.
It was another species of small flying dinosaur (Archaeopteryx) from this same time that is likely to have evolved into modern day birds with their beautiful diversity of song.
The rivers and streams tumble down from precipitous mountain ranges quite close to the inland lake. At the lake their rapid pace slows and their sandy load is dumped around the shallow lake’s edge in extensive fanlike deposits. These deep sediments are the same grey mudstones and golden sandstones that we see today in roadside cuttings through the Barrabool Hills and the Otway Ranges.
Note 3 – Ancient sands>
The landlocked lake steadily fills with sediment and plant material from the surrounding hills. Accommodatingly the lake bottom slowly subsides creating a shallow swampy environment that continues for millions of years resulting in sandstone and mudstone deposits of over 1,000 metres deep in some places. Note 4 - Barrabool Hills sandstone>
Our time machine carries us forward to 85Ma ago and now the super continent of Gondwana is showing signs of breaking up. Australia is beginning to split away from Antarctica, the beginning of a long process that takes another 55Ma. Eventually Australia drifts free and begins its slow passage north toward the equator and a warmer dryer climate at the dizzying speed of 6cm/year.
About 35Ma, before Australia brakes free, an immense comet estimated to be 10 km wide hits planet earth near the Gulf of Mexico. It is thought that its impact would have released an amount of energy equivalent to more than a billion Hiroshima bombs.
After this life on earth is changed forever and planet earth experiences a mass extinction of three quarters of all its plants and animals. The era of dinosaurs comes to an end and the era of mammals begins.
and the birth of the Barrabool Hills (added 7/8/17)
As time travelers we discover that as Australia drifts north its climate gradually warms and dries. During this journey Australia experiences ice ages and a two hundred year drought. Eventually the seasons also change from endless mild summers and dark freezing winters to warm summers and mild winters with transitional seasons in between. Australia’s unique flora and fauna begins to emerge, adapt and evolve. It is around this time that the Barrabool Hills is born.
Our time machine arrives at 30 Ma ago and we feel the earth shake violently as we experience the first of a long series of huge earthquakes that lift the ancient freshwater lakes above the surrounding area.
Eventually these ancient lakes of Gondwana dry out and the sea invades surrounding areas making the Barrabool Hills an island surrounded by shallow seas rich in marine life. Note 5 - Waurn Ponds Limestone>
These powerful earthquakes slide along fault lines in the sandstone and evidence of these faults can be seen today as steep hills at the southern edge of the Barrabool Hills running from Pollocksford to Ceres Bridge (the Barrabool fault) and Queens Park to Newtown (the Newtown fault). These faults have remained active to modern times and bit by bit the Barrabool Hills has been lifted more than 90 meters above the Geelong coastline.
While the Barrabool Hills is being raised above the surrounding plains by regular earthquakes, its deep sandstone is being sculpted by extreme weather including an ice age that begins 2.4Ma ago. At this time the earth’s climate becomes very cold and glaciers cover parts of southern Victoria.
Also during this time the night skies become a spectacular sound and light display as volcanoes erupt and shimmering hot lave flows out over the plains and fills river valleys shifting and blocking rivers creating inland many lakes. This continues throughout most of southern Victoria until a few thousand years ago, but it has very little effect on the Barrabool Hills that now stands high above the lava covered plains to the west.
Our time machine stops once again at 11,500 years ago when the climate is beginning to warm significantly. So much so that the polar ice caps partly melt and the sea level rises. From our elevated view on the top of the Barrabool Hills we watch the sea rush in and cover the vast coastal grassy plain to the east of Geelong, now called Port Phillip Bay. Tasmania also becomes isolated from Victoria as Bass Straight floods and the narrow connecting land bridge regularly used by migrating marsupials and the first Australians, is covered with by seawater forever.
Its 8,000 years ago and our time machine is just ticking over, allowing us to watch the Barrabool Hills slowly wear down. This is a warmer wetter period and small creeks rush down the slopes after heavy rains and erode the ancient time hardened sands, carrying them north to the Barwon River. Once part of the Barrabool Hills, the Barwon River was pushed to the north as the hills rose.
Regular upward fault movement of the Barrabool Hills keeps the creeks energised, enabling them to cut deep into the hard sandstone. Gradually over time the undulating hills and the fertile valleys that we admire today begin to assume their familiar character.
From freshwater lakes to abrupt hills, from sandy aquatic deltas to deep hard sandstone, these remarkable changes took tens of millions of years. Impassively and gradually, like an immense rudderless ark, the great continent of Australia journeyed from the Antarctic Circle to the equator, a passage that caused Australia’s climate to change very slowly and steadily but radically.
The Barrabool Hill’s lush towering conifer and gingko rainforest in a protected swampland has gone forever. It has given way to temperate grassy eucalypt and casuarina woodlands that have adapted well to exposure to strong winds, dry hot summers and mild winters.
The plants of Guandwana have been replaced with a hardier mix of plants that is unique to the Barrabool Hills.
How these modern plants have evolved and were modified by the first Australians who arrived over 50 thousand years ago will be explored in the next blog.
Book your seat for our next journey back in time on the wonderful time machine.
The Barrabool Hills vegetation. Part 2 – The arrival of Homo sapiens
To be posted in September
Stephen Murphy is qualified in Geology and Environmental Management and has been a nurseryman and a designer of natural landscapes for over 30 years. He loves the bush, supports Landcare and is a volunteer helping to conserve local reserves.