Australia has unique animals and plants, including the platypus and the waratah.
Australia is an ancient land. Some Australian fossils are around 3.5 billion years old. Some of its surface rocks are about two billion years old, while one Australian plant, the Wollemi pine, belongs to a family that has been growing on the continent for about 200 million years. And the history of modern humans inhabiting Australia goes back tens of thousands of years.
Australia has unique animals and plants, including the platypus and the waratah.
Inside planet Earth, everything is so hot that even the rocks melt. The heat comes from radioactive atoms breaking down, and it makes the liquid rock move around like boiling water in a saucepan. Luckily, melted rock moves much more slowly than boiling water.
The Earth’s crust, the solid rock we live on, floats on this hot liquid rock. Sometimes the molten rock breaks through, making a volcano, but mostly it spreads out sideways under the Earth’s surface. Then the molten rock gets cooler and sinks again.
A hundred years ago, some people noticed that, on maps, South America and Africa looked like they fitted together, just like two pieces of a jigsaw puzzle. That made them think that the seven continents—Europe, Africa, Asia, Australia, Antarctica, North America and South America—must have moved around. And so they came up with the idea of ‘continental drift’.
They could also see patterns in the way certain animals had lived in certain places—especially monkeys, camels, horses and birds. These patterns made sense only if the continents had moved. The problem was that nobody could explain what made them move.
A platypus that bites!
There is an opal in the Australian Museum in Sydney that, around 110 million years ago, was the jaw of an animal like a platypus. This little animal had teeth, but adult platypuses do not have teeth now. The jaw was found at Lightning Ridge in New South Wales. It came from a relative of Australia’s modern monotremes—echidnas and platypuses.
About 50 years ago, scientists realised that the pieces of the Earth’s crust, called plates, can move. They get pushed along by currents in the molten rock below them. That gave rise to the term ‘plate tectonics’.
Today, the big plate that includes all of Australia, New Zealand and New Guinea moves north at about 67 millimetres a year.
The plates are huge, but so are the forces moving them. These forces can cause earthquakes, and they can also rip plates apart. Luckily, Australia is in the middle of a stable, single plate, and so it does not have many earthquakes.
The supercontinents divide
We now know that once, very long ago, there was just one large area of land called Pangaea. The plants and animals on Pangaea could live anywhere around the land, and so they either evolved, by slowly changing to suit their surroundings, or they died out.
Pangaea then split into the supercontinents, Laurasia and Gondwana, and different groups of plants and animals evolved separately on each one. Then, when Gondwana split into separate continents, including Australia, lots of evidence was left behind.
For example, while Australian plants from the family Proteaceae—which includes banksias, waratahs and grevilleas—were found all over Gondwana, they are also related to other members of the family in southern Africa and in South America.
Today, the big plate that includes all of Australia, New Zealand and New Guinea moves north at about 67 millimetres a year.
Similarly, most people think marsupials like kangaroos, possums, koalas, bilbies and Tasmanian devils are found only in Australia, but the American opossum evolved from the same animals found on Gondwana that became Australia’s marsupials.
Flightless birds, called ratites—like the emu, the cassowary, the African ostrich, the South American rhea and the now extinct New Zealand moa—were also found on Gondwana.
Around 220 million years ago, in what is called the Late Triassic period, the supercontinents began to separate. Gondwana later broke up, and the Australian continent drifted south. As the plates moved, the animals and plants that lived on them were carried along with them. Fossils were formed in the rocks, and by studying them we can work out what once lived there.
People who study fossils and the rocks in which they are found are called palaeontologists. They are like detectives searching for clues. By examining minerals called zircons in New Zealand rocks, they can actually detect that those rocks formed from sediments that came from rocks in New South Wales and Queensland over 150 million years ago!
Australia and its animal and plant life are the way they are because of how our continent formed and changed.
An ancient land
Australia and its story have been shaped by rocks, and some of those rocks are amazingly old. When people began studying rocks some 200 years ago, the oldest rocks they discovered were in Wales, in the United Kingdom, so geologists called them ‘Cambrian’, from an old name for Wales.
Scientists now think that the Cambrian period dates back to 542 million years ago. They used to think that was when the first fossils were formed. Planet Earth is almost nine times older than that, and all the rocks older than 542 million years old are called Pre-Cambrian. In Australia, some of those older rocks contain fossils.
Who came first?
QUESTION: The type of pouch that the koala and the wombat each has suggests that they are related, but who evolved first?
ANSWER: The females of both species have a pouch that faces backwards (or downwards in the koala). This stops dirt getting into the pouch. That is very useful for a burrowing animal like the wombat, but it is less useful for an animal that climbs trees! That is how we know that the wombat must have come first.
Life has existed on the continent of Australia for a very long time, and the rocks and soil are also very old.
Fascinating fossils
In Western Australia, there are fossils of stromatolites— a very basic form of life—that are at least 3.46 billion years old! Living stromatolites can be found near Shark Bay, while some of the world’s oldest fossils (that we recognise as animals) have been found in the Ediacara Hills in the Flinders Ranges of South Australia.
Life has existed on the continent of Australia for a very long time, and the rocks and soil are also very old. In Europe and North America, glaciers in each ice age stripped all the surface rocks away, leaving fresh rocks that made new soil when the ice melted. However, very few glaciers have formed in Australia in the past 100 million years, and so there is very little new soil.
New soil also comes from volcanoes, especially at the edges of a plate. Our continent is a long way from the plate edges, and Australia has only a few small volcanoes. Because of this, most Australian soils are old and worn out. They lack certain minerals, such as phosphate, that plants need to thrive. The lack of minerals in our soil has affected the evolution of life in Australia.
Biodiversity—having lots of different species— is important for the future of life on the Earth. Most people think the greatest biodiversity is found in rainforests, but Australia’s greatest biodiversity is found in some of Western Australia’s sand hills, where everything plants need to live on is in short supply. That means that the species that live there have had to evolve just to survive.
Almost every species of Australian plant and animal has characteristics that help it live in the Australian climate. In such a dry land, bushfires occurred even before humans came. To survive bushfires, animals must be able to find shelter, and plants must be able to grow back after a fire has passed through. That is why Australian native plants often have woody fruits that protect the seeds and open up only after a fire.
The early settlers were disappointed to find no beasts of burden in Australia—no horses, mules or oxen— and very few trees that produced good timber to use for building houses. That was because the animals and plants that lived here had to concentrate on one thing: survival.
Scientists can learn about ancient times from old emu eggshells around Lake Eyre in South Australia. They analyse them and, from some of the atoms in the shells, they know what the climate was like when the eggs were laid. Then, carbon dating shows how old the shells are, so we can tell what Australia was like 50,000 years ago.
From fossil remains, scientists have also worked out that about 360 million years ago there was a drought just outside the present-day New South Wales town of Canowindra. We know it was a savage drought because we have evidence that many fish huddled together for safety in one billabong. Then the drought got worse and all the fish died, taking their last breath in the sticky mud.
Not long after that, the rains came again. The dead fish were covered with a layer of sand that pressed them down into the mud. That was the start of the process that made them into the fossils that can be seen in Canowindra today.
In many ways, fossils can teach us a lot about the history of our land.
The age of giants
The ice ages caused glaciers in the Northern Hemisphere, but there were few glaciers in Australia, where it got colder and drier instead. The sea levels dropped as well, so the whole of Bass Strait was dry land. Tasmania and Kangaroo Island, as well as many smaller islands, were part of the mainland. The Torres Strait was also dry land, which is why gum trees, wallabies, cuscuses and even echidnas are found in Papua New Guinea. After the last ice age, the sea level rose again, and that is when many of Australia’s best harbours were created.
Magnificent megafauna
The cool, dry climate may have had an even bigger effect. Today, the biggest animal in Australia is probably the saltwater crocodile, but in the past there were many larger animals on our continent. Some of them died out a long time ago, like the dinosaurs whose fossils can be found at Dinosaur Cove in Victoria, Winton in Queensland and other sites.
In the middle of the nineteenth century, members of the British public were very excited about dinosaurs. The white people living in Australia knew nothing about our fossil dinosaurs, but they did know that some very strange animals had once lived in Australia. Sadly, they knew them only from their bones.
A hippopotamus?
The Diprotodon, an ancient relative of the wombat, was the size of a hippopotamus. So explorer William Dampier was closer to the mark than he knew when he thought he had found the remains of a hippopotamus inside a shark at Shark Bay in Western Australia—although the Diprotodon was definitely extinct by the time Dampier arrived in 1699! From Dampier’s description, it was probably a dugong’s jaw.
The story begins with several explorer-scientists, especially Major Thomas Mitchell. These explorers visited caves in the Wellington Valley near Dubbo in New South Wales. What they discovered amazed them, because they thought they had found elephant bones.
Mistakes like that are easy for untrained people to make. When navigator and explorer William Dampier cut open a shark he had caught at Shark Bay in Western Australia in 1699, he found a jaw that he thought belonged to a hippopotamus. However, it was more likely to have come from a dugong—a large sea mammal.
Added to this, in the mid-1800s, scientists had been finding bones in Europe and North America which really had come from animals that were either elephants or their relatives—the mastodons and mammoths. That is why they were not surprised to find what they thought were elephant bones in Australia.
Today, the biggest animal in Australia is probably the saltwater crocodile, but in the past there were many larger animals on our continent.
Even experts could be fooled. The first of those bones was found by a wealthy squatter named George Ranken who had discovered the Wellington Caves by falling into one! While he was there, he retrieved some bones. He gave them to politician and clergyman John Dunmore Lang, who took them to Edinburgh in Scotland. From there, they went to French naturalist Baron Cuvier in Paris, in around 1830. Cuvier also thought the bones were those of an elephant.
In fact, what they had found was even more exciting. The bones came from a giant relative of the wombat called a Diprotodon. However, opinions varied. William Sharp Macleay, a trustee of the Australian Museum in Sydney, was one of the experts who looked at the bones in 1859. He called the animal a ‘gigantic species of native bear’— a giant koala.
The bones of an even more amazing animal were found in the Wellington Caves and several other places around Australia. This one was also a larger relative of the wombat and the koala, but it was probably a meat-eater. London palaeontologist Richard Owen gave it the name Thylacoleo, which means ‘pouched lion’.
Some people did not agree with Owen. Macleay thought it was descended from plant-eaters. Today, the animal is regarded as a meat-eater, although there is still no agreement about whether it hunted live prey or just scavenged off dead animals.
Perhaps the most spectacular of the ‘megafauna’, as these huge animals are called, was a giant monitor lizard related to the Komodo dragon and the goanna. Megalania prisca was six metres long—as long as a large car—and eight times the mass of an adult Komodo dragon. These reptiles will attack children and weak adults, so just imagine what the Megalania could do!
The giant predators probably ate herbivores, or plant-eaters, like the Procoptodon, a giant kangaroo. The megafauna certainly lived in balance with each other and their environment over much of Australia for a long time. Then, mysteriously, they died out at around the time the first humans arrived.
Some people think these giant animals died out because Aboriginal people hunted them, but that is unproven. One proof would be discarded megafauna bones with cut marks from stone blades and scrapers, but nobody has found any as yet. Besides, a number of giant animals like the Dromornis stirtoni, or Thunder Bird, and the Bullockornis planei, or Demon Duck of Doom, died out before humans arrived in Australia.
So it might have been hunting by humans, but it could also easily have been climate changes that killed off the megafauna in Australia.
