34 MILLION YEARS AGO
The earliest signs of separation between Australia and East Antarctica began around 132 million years ago. As Antarctica moved southward at a few millimetres per year, the Australian continental shelf suddenly drops away, forming a massive 5 kilometre deep canyon wall around 100 million years ago. Then the true seafloor spreading (the creation of new ocean crust) began around 96 million years ago.
By 34 million years ago, Antarctica had moved far enough south to become permanently glaciated, marking the beginning of the Antarctic ice sheets.
Over the next 4 million years, both Australia (including Tasmania) and South America had fully separated from Antarctica. This separation allowed the development of the Antarctic Circumpolar Current, which prevented warm ocean waters from reaching Antarctica and intensified global cooling. As a result, no land bridge existed between Tasmania, Australia, and Antarctica during the Oligocene, and large-scale animal migration between these landmasses was no longer possible.
As Antarctica became thermally isolated by the Antarctic Circumpolar Current, leading to hlobal cooling, the initial drying of the Australian continent begins. It becomes self-evident that the great Australian river systems are less stable in providing regular water to central Australia. This would have impact on the presence of inland seas or large lakes as they change their sizes with the season. As Australia moves further north between 23 million to 5 million years ago, the northern continent enters the subtropics, controlled more by monsoon weather patterns. However, further south, the interior became more arid. Forests slowly gave way to woodlands and grasslands, and seasonal lakes began to dominate the interior and remain there for a long time. While the lakes remained, Australia remained wetter than today.
But these would become much drier with the arrival of one species from south-east Asia.
38 to 26 MILLION YEARS AGO
The collision between the Indian and Eurasian plates began much earlier, around 50 to 55 million years ago (early Eocene). Around 34 to 23 million years ago, India was continuing to push into Eurasia, further uplifting the Himalayan mountain range and altering regional and global climate patterns.
From 25 million years ago to the present, India continued to push north against the larger continent to form the highest mountain in the world — Mount Everest. The presence of the Himalayan mountain range would slowly but surely change the climate to the west in places like the Middle East and northern Africa. Not exactly in favour of increasing rainfall as one would hope, but rather, the opposite. Despite this increasingly drying out effect due to reduced rainfall, plenty of valleys containing underground springs and small streams would support a reasonable amount of vegetation. It is only when animals move away from these green pockets that the number of trees quickly thin out and with large patchy areas of dry grass, and in some places where no plants existed we can see the beginnings of deserts. (1)
Many modern groups of animals were already established by the Oligocene, although most modern species had not yet evolved. If you could travel back in time, you would recognise early forms of many familiar groups such as mammals, birds, and reptiles, but often with notable differences in size, diversity, and ecological roles compared to today.
During this time, primates were diversifying into several major groups. Early anthropoids (the group that includes monkeys, apes, and humans) were present, particularly in Africa and Asia. These primates were mostly arboreal and lived in forested environments. The split between monkeys and apes would occur later, and open savanna habitats were not yet widespread environments for early primates.
35 MILLION YEARS AGO
The African plate continued to converge with the Eurasian plate during this time, contributing to the uplift of mountain ranges such as the Alps. This process began earlier and continued over tens of millions of years.
30 MILLION YEARS AGO
New Zealand had already been isolated from other landmasses for tens of millions of years by this time. Its bird life evolved in isolation, leading to unique species, including early parrots. With few terrestrial predators, many birds evolved flightlessness and other unusual traits, including remaining unafraid of humans and other introduced species, much to their detriment. Today, there is a push to preserve the animals from introduced domestic animals, such as cats and dogs, and placing them on more isolated and smaller islands for the population of rare native species to slowly increase.
28 MILLION YEARS AGO
The first direct evidence of what has been described as an apocalyptic comet colliding with the Earth has been found by scientists. The dirty snowball of ice and dust weighing at least 20 tonnes appeared over Egyptian skies and exploded in the atmosphere approximately 28 million years ago, raining down a massive shock wave of fire that killed everything in its wake over the Sahara desert below. The result of the shock wave was the melting of sand to a temperature of 2,000°C forming a yellow silica glass that can be found today scattered over an area larger than the state of Delaware (or more precisely, 6,000 square kilometres). Some of the glass was noticed by ancient jewellers in more recent times and now adorn various man-made artefacts such as King Tutankhamun's scarab broach.
In addition to this, an Egyptian geologist Aly Barakat found a black pebble weighing 30 grams embedded inside some of this glass in December 1996. He sent the pebble to Marco Andreoli at the University of the Witwatersrand in South Africa. The discovery of this pebble turned out to be an absolute bonanza (and somewhat unusual in the sense that any evidence of comets colliding with the Earth tend to be microscopic dust moving high up in the atmosphere). On further analysis, the team of reputable South African scholars consisting of geoscientists, physicists and astronomers were hedging their bet that this pebble came directly from the comet.
"NASA and ESA [European Space Agency] spend billions of dollars collecting a few micrograms of comet material and bringing it back to Earth," said Professor Jan Kramers, a member of the scientific team involved in the analysis and who is the head writer for the article to discuss the discovery. "Now we've got a radical new approach of studying this material, without spending billions of dollars collecting it."
Of course, as with any scientific study, there is always going to be some debate as to whether the pebble was really part of the comet fragment (healthy skepticism is what keeps science well-balanced in its knowledge). As Ingo Leya at the University of Bern in Switzerland said:
"The problem is, we have little cometary material as a standard to compare with. Therefore, it is difficult to firmly conclude or exclude that this meteorite comes from a comet." (Grossman, Lisa. 'Black glass' could be first comet chunk found on Earth: New Scientist. 10 October 2013.)
Yet even Leya concedes the evidence that the pebble came from outer space is rather convincing to say the least. Among the interesting evidence to support the "extraterrestrial component" of the pebble according to Professor Kramers is the high carbon content, much higher (roughly 65 per cent) than are found in any meteorite sample (usually only 3 per cent). Also, the pebble contained isotope ratios of certain noble gases not found in meteorites or naturally here on Earth, leading the South African researchers to believe this pebble had to come directly from the comet itself.
The impact of the comet with the Earth's atmosphere and the subsequent explosion and shock wave had also helped to form tiny microscopic diamonds inside the pebble. A useful observation as not only would this prove the pebble was right in the middle of the action when the explosion occurred, but also scientists could determine the likely size and speed of the comet fragment (yes, the 20 tonnes is a conservative figure with the rest of the comet likely to have been much larger before it broke apart) thanks to our knowledge of how high the temperature and pressure had to be in order to form the hardest known substance in the universe (i.e., diamond).
Among the scientists involved in this discovery included Professor Jan Kramers of the University of Johannesburg (a geochemist and isotope geologist), and astronomer Professor David Block of South Africa's University of the Witwatersrand (known affectionately as Wits University). Further details are published in Earth and Planetary Science Letters towards the end of 2013.
27 to 28 MILLION YEARS AGO
The evolutionary origins of the plant genus Cannabis are still debated. Fossil pollen evidence suggests that its ancestors were present in Central Asia originating in a mountainous region of Kazakstan by the Miocene (around 20 million years ago), although the lineage may extend further back into the Oligocene. These plants likely evolved chemical compounds such as tetrahydrocannabinol (THC) and cannabidiol (CBD) as defence mechanisms against herbivores (it tastes pretty bad) and environmental stressors, including ultraviolet radiation — a natural ageing factor.
Humans began using Cannabis much later, within the last 10,000 years, initially for fibre, food, and eventually for medicinal and psychoactive purposes, especially during times of great physical pain or helping to see beyond what our eyes can observe to see certain hidden patterns in life and nature. People would learn the medicinal secrets of the plant due to the presence of another chemical component known as Cannabidiol (CBD) which provides strong anti-inflammatory and, oddly enough, anti-psychosis relief (should it be needed). Probably a good thing considering life was hard and highly stressful (and may even be very painful if you get attacked by a predator leaving behind serious wounds or broken bones to recover from). Eventually people learned about the THC component of the plant for relaxing the mind and developing a high euphoric feeling as well as controlling pain levels. However, due to the risk of developing the psychosis effects of schizophrenia (due to the way prolonged use of the chemical THC causes the frontal cortex to stop functioning) for a small number of people, and to a greater extent a loss of short-term memory among the young people, it is illegal for people to grow and use the plant. But in the past, it was difficult to control its use, especially among the male population who saw a need for it.
25 MILLION YEARS AGO
A number of mammals have grown in size to become the largest of its type across all the continents of the world (including Australia). They would never reach the enormous size of those terrible reptiles called the dinosaurs, but compared to the animals of our times, these were big creatures.
For example, whales evolved from land-dwelling mammals no bigger than a small horse with sharp teeth, four small legs and a tail, during the Eocene, well before the Oligocene. By the Oligocene, early whales had already become fully aquatic and diversified into two major groups: toothed whales and baleen whales. Some species were large predators, while others began adapting to filter-feeding lifestyles.
Some shark lineages during this time evolved into very large forms, including ancestors of the giant shark Otodus megalodon, considered at least twice as large as the biggest modern day great white sharks, although this species itself appeared later. Evidence for this observation can be found in the massive fossilised shark tooth collected from the Tasman sea floor in 2003 by CSIRO marine research scientist Dr Alan Williams during the joint Australia-New Zealand NORFANZ research expedition (2).
However, as food supplies dwindled in the cooler oceans of the world and along the shoreline, these massive predatory whales would eventually die out, leaving behind a handful of other whale species with better survival rates because of their greater reliance on alternative food sources, such as plankton.
As for sharks, the smaller species tend to adapt better to the lower food quantities in the oceans, becoming a little more agile and reducing their energy needs. Anything excessively large for a shark would struggle to find enough food to meet their daily energy requirements as they moved their larger, somewhat cumbersome bodies through the water.