Cretaceous period
144 to 64.5 million years ago

130 MILLION YEARS AGO

The first flowering plants spread throughout the world.

94 MILLION YEARS AGO

Earth in the mid-Cretaceous period around 94 million years ago. Image © 1997 C.R. Scotese is available from http://www.geologie.uni-stuttgart.de/down/maps2/pl10.jpg.
The Cretaceous Period marks the time for another major break-up of the great northern and southern continents of Laurasia and Gondwana. North America drifted apart from Europe, while South America moved away from Africa. India had already moved away from Antarctica and was now situated at the equator.
While the continents were splitting apart, sea levels began to rise, resulting in the low-lying areas between the Eastern and Western halves of North America, and Europe and Asia, being flooded.
Dinosaurs still flourished at this time. However, the cooler conditions of the Cretaceous Period meant the great forests were becoming less heavily populated and increasingly more patchy, especially in the lands covering the far northern and southern latitudes. A diminishing forest size and greater treeless "savannah-like" environment (ie. very little grasses as the ground-covering ferns competed well for the light) also meant there was less and less food available to support very large animals on land. Eventually, a time came when the massive plant-eating and carnivorous dinosaurs of the Jurassic Period gave way to smaller and more agile dinosaurs of the Cretaceous Period.

Australia and Antarctica were once a single continent nearly 80 million years ago. (Source: Petroleum Exploration Society of Australia web site, 2007).

75 MILLION YEARS AGO

The rise in sea levels created isolated communities. Dinosaurs that existed at this time had diversified into unique forms based on their location.
Extensive innundations of the Australian continent by water was known to have occurred. Later, these waters would regress to form a large inland sea covering much of the enormous depression of central Australia (first formed during the Triassic and Jurassic Periods). As time passed, rain falling on the surrounding mountains helped to replenish the Australian inland sea and turn it into a large body of freshwater.
Regression of the inland sea in central Australia began or had accelerated during the Pleistocene Epoch with the arrival of the first aborigines from Asia. Today, the only remains of this inland sea is a small body of water (only when the rainfalls in Australia are unusually high every 10 to 20 years) known as Lake Eyre. (1)

70 MILLION YEARS AGO

Artist impression of Australia and Antarctica joined together nearly 70 million years ago. Dinosaurs would continue to exist on this land mass. But the colder conditions would see dinosaurs get smaller and more agile. Larger dinosaurs would only move south when the conditions became warmer and migrated back to the northern regions towards the end of the summer months. Image © 2007 ABC documentary Dinosaurs on Ice.
According to Anusuya Chinsamy-Turan of the University of Cape Town, South Africa, the cell structure of reptilian bones show it responds to climate change on a seasonal basis and/or variation in food availability.

Anusuya Chinsamy-Turan of the University of Cape Town, South Africa. Image © 2007 ABC documentary Dinosaurs on Ice, written and directed by Ruth Berry.
For example, when food is scarce, a distinctive and narrow growth ring appears showing the bone has reduced growth. When food is plentiful, the growth of the bone is quicker.

Growth rings in reptilian bones. These rings are not observed in mammals. Image © 2007 ABC documentary Dinosaurs on Ice, written and directed by Ruth Berry.

Marked here are the rings showing the reptile had reduced food supply. Image © 2007 ABC documentary Dinosaurs on Ice, written and directed by Ruth Berry.
These rings can be due to variation in climate change when food becomes scarce in winter, and in the summer becomes more plentiful. But other factors can also produce these rings. For example, a larger and less agile reptile is likely to have growth rings in its bones than a smaller and more agile and active reptile.
When dinosaur bones are analysed, scientists discovered they can have growth rings and no growth rings. Where the dinosaurs have no growth rings, it is usually because the animal has access to a plentiful supply of food all year around. Where the growth rings exist, something in the environment would see the dinosaurs go without food for a period of time before the food supplies returned in abundance.
In the case of the cell structure of bones from a common plant-eating dinosaur known as Hadrasaurs found on the continent of Antarctica and in the land mass lying over the Arctic region (to become Alaska today), Chinsamy-Turan noticed there were no growth rings. These are relatively large animals about the size of a bus whose bones are found in relatively cold polar regions of the planet.
Scientists are certain Antartica would have experienced snow in the winter time. But dinosaur bones discovered on this continent showed no growth rings. Likewise the same thing can be observed for dinosaurs found in the Arctic region. Why?

A sample of dinosaur bone extracted from Alaska. Image © 2007 ABC documentary Dinosaurs on Ice, written and directed by Ruth Berry.
Either these allegedly cold-blooded dinosaurs had somehow found a way to adapt themselves to the cold, or they constantly migrated to follow the warmer conditions.
If dinosaurs did migrate, the larger variety of creatures would have to produce one or two relatively large offsprings in the early summer months near the polar regions (the time when there would be less predators around). As soon as they were born, the offsprings needed to eat plenty of food quickly during the summer months to gain rapid growth while the parents protected them from the numerous smaller predators living in the polar regions (compared to those near the equator) until they were ready to migrate to warmer areas when winter returned.
However even if these hardy polar dinosaurs did find a way to adapt to the cold, the entire planet would eventually plunge into darkness and experience a more intense cold lasting many months and potentially years when a natural catastrophe hit the Earth around 64.5 million years ago. When the warmth finally returned , the dinosaurs would no longer exist. Something suggests the dinosaurs didn't quite have an adequate mechanism to adapt to the cold (well, not the intense cold), especially the larger ones and certainly not enough to survive the prolonged periods of food scarcity for the smaller dinosaurs. Scientists are now facing the possibility that polar dinosaurs (especially the larger ones) probably had to migrate from Antarctica into Australia and in the land bridge connecting the Arctic region to the warmer North American and Asian regions to access the more reliable and plentiful food supplies in warmer areas and so maintain the normal growth patterns in the animals for longer. And they had to migrate when the conditions were warm enough. Otherwise the bones of polar dinosaurs must show evidence of growth rings, which they do not based on the bones uncovered so far.
Where bones with no growth rings are found in the polar regions at this time, we must presume they were from polar dinosaurs that died naturally from old age or natural disasters, or were attacked by predators during the warmer months (and not during the winter). They need not be evidence that dinosaurs were adapting to the cold conditions at winter time. It is currently the most logical explanation based on the evidence at hand.

64.5 MILLION YEARS AGO

A massive reduction in the number of animals occurred because of some kind of natural calamity. All dinosaurs, many early marine birds, and some plants that lived in the watery environment, soon disappeared. Although the number of dinosaurs were already on the decline to a certain extent in various parts of the world nearly 100 million years ago, scientists are now convinced that at least one asteroid was responsible for the extinction of the dinosaurs at around this time.

And now scientists feel pretty sure that this asteroid really did collide over land (2). The result of the impact was a sudden reduction in worldwide temperatures affecting much of life on Earth.

Artist impression of the collision between the Earth and the asteroid which destroyed all the great dinosaurs.
According to a team of geologists led by Dr Walter Alvarez, it is believed that at least one large asteroid ranging from 9 to 16 kilometres in diameter collided with the Earth in an area now covered by the Gulf of Mexico (not far from Mexico's Yacatàn peninsula). Apparently the point of impact, known as the Chicxulub crater, was once part of the central American landmass until the asteroid smashed into the ground, exploded, and threw up great quantities of fine soot and dust high into the air, causing the entire planet to dramatically darken and cool down in a matter of weeks.

The impact site for the asteroid that killed off most, if not all, of the dinosaurs. Fossilized tree debris mixed up with ocean floor sediments have been found in the Gulf of Mexico suggesting massive tidal waves had washed back and forth over the impact site, uprooting trees and sending them out to sea in its wake. Source: Norman 1991, p.153.
In the extremely cold and dark wintery conditions that prevailed over the next 10 years, there was a massive reduction in the supply of rich tropical-like plants needed to keep the large plant-eating dinosaurs alive. Since most dinosaurs lacked an (or had a poor) internal temperature regulating mechanism to keep their bodies sufficiently warm for long periods of time, the entire ecological chain, from the great plant-eating dinosaurs to the great meat-eating dinosaurs and almost everything else that heavily depended on the existence of the dinosaurs for its survival, soon perished.

Earth towards the end of the Cretaceous period around 69.4 million years ago. Image © 1997 C.R. Scotese is available from http://www.geologie.uni-stuttgart.de/down/maps2/pl11.jpg.
In total, nearly 76 percent of species, 47 percent of genera, disappeared in a matter of a decade or two.
One of the few living descendants of the ruling reptiles is the Crocodile. Crocodiles have survived to the present-day thanks to their locality (found mainly in the tropics), size (a small body requiring less food) and adaptation to a watery environment (water maintains a reasonably constant and relatively warm temperature).
For other animals, hibernation and living underground where the temperatures are warmer and remains constant probably played a crucial role in their survival during this apocalyptic event.
The seas retreated at this time. Those areas of land covered shallowly by sea water quickly dried up. (3)
## SPECIAL UPDATE ##
26 October 2006
A team of paleontologists led by Professor Gerta Keller of Princeton University in New Jersey, USA, claims to have found scientific evidence to support the view that the impact at the Chicxulub site was probably not enough to destroy the dinosaurs. Keller and colleagues think there was one larger and more devastating impact about 300,000 years after the first impact. Together with massive volcanism in the Deccan Flood Basalts in India pushing the species to the brink of extinction and the accompanying massive global warming formed by the copious greenhouse gases from the volcanoes raising temperatures by 3 to 4 degrees in the oceans (or 7 to 8 degrees on land), were enough to bring down the dinosaurs.
As Keller said:
'The Chicxulub impact alone could not have caused the mass extinction because this impact predates the mass extinction.' (National Science Foundation web site. 17 October 2006.)

Gerta Keller
The team supports this view through an analysis of the Cretaceous-Tertiary (K-T) boundary containing anomalous levels of excessive iridium (the evidence for an asteroid impact) at 12 sites (including the Yacatan peninsula and in independent locations such as in Beloc, Haiti). More detailed analysis showed how the Chicxulub crater predates the Cretaceous-Tertiary boundary by about 300,000 years after examining the pattern of reworked glass spherules ejecta (another form of evidence for an asteroid impact) in higher quantities above the K-T boundary.
Because of the different layers for the spherule ejecta material and the iridium anomaly in the K-T boundary, it is difficult to see the two as part of a single impact event. Some scientists tried to reconcile the difference by saying a megatsunami allowed the ejecta material to settle first before the finer iridium layer deposited on top. But this should have occurred in a matter of days after the impact.
However Keller and colleagues noticed at various sites how the layers are separated sufficiently and contained microfossil evidence of burrowing organisms inbetween the layers suggesting a much wider time frame. That time frame has been calculated in the hundreds of thousands of years, not a few days.
These results were presented on 24 October 2006 at the annual meeting of the Geological Society of America in Philadelphia, USA.
Just one problem: evidence for the second crater or craters responsible for the mass extinction remains elusive and as such it should be called Keller's hypothesis. Nevertheless, it is a good hypothesis and would need further work by other scientists to get to the bottom of this catastrophic event(s) leading to the death of all the great dinosaurs.
## SPECIAL UPDATE ##
2 December 2006
A research team led by Professor Ken MacLeod of the University of Missouri-Columbia has released findings in the Geological Society of American Bulletin stating in the words of Professor MacLeod:
'It's a completely straightforward, single-impact scenario. It was a haymaker that nobody saw coming. One shot, and that's all you need to explain it.' (Dunham, Will. The Sydney Morning Herald: Dinosaur's end: new study backs one-shot theory. 2-3 December 2006, p.19.)

The evidence presented this time involved a sediment core drilled below the ocean nearly 4,500 kilometres from the Yacatan impact site. The distance is important because any drilling at the impact site would not deliver accurate results following the expected earthquakes, landslides and other events that would come to alter the impact site. On extracting and analysing the core, the scientists have found a single layer of impact-related material. There is no additional layer above or below the main layer. The only explanation based on this finding: the event that ended the dinosaurs was a single catastrophic event.

NOTES

The current dry conditions on the western side of the Blue Mountains in Australia could be reversed by recreating a huge, permanent inland sea in the central part of the continent where Lake Eyre is located. The aim would be essentially to create a giant natural desalination system using the dry, hot northwesterly winds in the summer to pick up enough water from the inland sea and transport it to the Blue Mountains where the probability of rainfall should increase as required to fill the great river systems of south-eastern Australia.
Depending on the height of the Blue Mountains (since it has been weathered away after many millions of years) and the amount of plant cover for keeping moist on the ground (which is, unfortunately, on the decline because of the impact of humans through land clearing and natural bushfires through lightning strikes), the moist westerly winds should rise up along the Blue Mountains to fall as rain on a more regular basis and stay on the ground longer with the trees and shrubs acting as ground covers. If enough rain falls, the rivers and creeks of Barcoo, Thomson, Coopers, Diamantina and Georgina in Queensland; the Hay, Todd and The Finke rivers in Northern Territory; and The Alberga river in South Australia will fill and eventually bring the great inland sea back to its former glory.
However, the amount of water needed to affect humidity in the air to create rainfall on the Western side of the Blue Mountains would have to be vast and only by channelling water from a vast source into Lake Eyre (eg. the southern oceans or from the Northern Territory wetlands during the wet season) together with plantings of massive forests to retain the water on the ground could Australia benefit from losing the infamous title of being the world's driest continent.
Pumping of water may be necessary in the early stages to get enough water onto dry land. This could be done from a place like Port Augusta in South Australia. Or alternatively, during the wet season, water in the Northern Territory could be directed to follow along a shallow man-made channel into the Georgina River where the water can eventually find its way into Lake Eyre.
For example, pumps could be built in the town of Port Augusta to help move just enough ocean water to pour into a shallow and narrow man-made channel starting near this town. Because the central Australian continent is relatively flat, one would think it is possible to carve a channel all the way to Lake Eyre. But just in case it isn't, the shallow and narrow man-made channel could be made to snake around small mountains and hills until it reaches a point where the land is below sea level or reaches Lake Torrens! Well, it should be much easier than building the Panama Canal in central America!
Once this lake is filled, another shallow cut into the land may be necessary until water can flow with the help of gravity directly into Lake Eyre.
However, some skeptics argue such an ambitious project would be nothing more than a pipedream. The primary reasons being that (i) no pump can push water all the way to Lake Eyre; (ii) digging holes below sea level to allow gravity to force sea water through to Lake Eyre would take too long and be very expensive; (iii) the cost of digging the canal on the surface is too expensive (presumably for allowing commercial ships to travel through it); and (iv) there was no discernible difference in the local climate at Lake Eyre or its neighbouring areas of the basin.
As Vincent Serventy, author of The Desert Sea - The Miracle of Lake Eyre in Flood said:
'In 1883 a scheme to flood the bed of Lake Eyre was investigated. It was suggested a canal be dug from Spencer's Gulf to Lake Torrens, and then north to Lake Eyre. It was soon discovered [at the time] that the cost of digging the canal would be enormous, too much even for the wildest optimists.
'Sceptics also pointed out that, despite the large area of the Red Sea, it was still surrounded by deserts, contradicting the belief that creating an inland sea would produce a mild climate with heavy rainfall in the surrounding country.
'That this belief was a fallacy was proved beyond doubt when Lake Eyre was eventually filled, with water from her own natural canals, the web of rivers running into it; there was no dramatic change in the local climate.' (Serventy 1985, p.24.)

However, in 1883, people didn't have huge earthmoving machines and more powerful explosives. In those days, horse and carriage, steam engines and brute force from people hand digging the canal would have been the best anyone could do. Also the winds for carrying moist air had to travel further to a mountain range to create clouds and with it rain.
This is possible with the help of the Blue Mountains.
We also don't need to dig a very deep trench for commercial ships to travel through. A canal not more than a metre deep and perhaps five metres wide should be more than adequate. As for taking the straight line route to Lake Eyre, the cost to blast through some small mountain ranges would probably make it a very expensive exercise. However, to reduce costs, the canal could be made to go around the mountain ranges.
As for the local climate argument, it is unlikely people will be living in or near Lake Eyre simply because the humidity in the air would require a substantial mountain range like the Blue Mountains to create clouds and eventually rainfall. And anyway, if the project is successful, the regular floods heading its way to the people living near Lake Eyre would probably put an end to their potentially cosy existence in the central part of Australia.
Perhaps we need to have another look at this idea more closely to see what is possible today rather than relying on old data from last century.
## SPECIAL UPDATE ##
January 2005
A plan in the pipeline from West Australian Liberal Party leader Colin Barnett suggests an untested 3,700-kilometre pipeline canal to pump water from Fitzroy River in the Kimberleys to the city of Perth could be built. Now that Perth is slowly reaching a crisis point in its water supplies, either a desalination plant near Perth or a pipeline to transfer the freshwater to the city should be built soon. However the pipeline project will be expensive and more work is needed to determine the feasibility of such an ambitious project.
## SPECIAL UPDATE ##
10 April 2005
The WA Government in Perth has given the go ahead to build a 50 megalitre desalination plant based on the reverse osmosis process. This is a tiny fraction of the 1,030 megalitres used by the population in Perth, but every fresh water it can produce will be seen as valuable.

David Raup, a geologist at the University of Chicago, suggested that 'As much as 60 percent of all extinctions may have been the result of asteroid impact.' (Lewin 1993, p.77)

Photograph of David Raup © Patricia Evans.

Perhaps great polar ice caps were formed soon after the asteroid impact which helped to trap a large amount of the water in the oceans and so reduce sea levels around the world.