Whatever caused the massive extinction at the end of the Permian period, methane levels reached a high level in the atmosphere and later fluctuated widely from the expected normal levels of around 2,200 parts per million between 278 million and 250 million years ago to roughly 5 major peaks spread out over the next 15 million years with the first one being the biggest at around 4,400 parts per million nearly 250 million years ago.

During these high methane levels and greater global warming conditions, the interior of the great supercontinent appeared more desert-like because conditions on land were initially very hot and dry. Only the coastal regions were humid enough to support ground-covering ferns, tree-like ferns such as Dicroidium, conifers and cycads, and an increasingly more diversified and flourishing insect population.

Then the conditions began to cool down a little and rainfall increased. Soon the plants edged its way towards the interior of the supercontinent until much of the land became a huge tropical forest.

 
Again, there was another tremendous burst in animal numbers over the next few million years. But what differed in this sudden burst (in geological terms) in life compared to the Cambrian period was the greater numbers of animals of a particular theme rather than an all out innovate stage of evolution.

As Roger Lewin, author of Complexity: Life at the Edge of Chaos, wrote:

'...there have been tremendous bursts of innovation...in the history of life, mostly in the wake of mass extinctions. For instance, following the Permian extinction some 250 million years ago, in which an estimated 96 percent of existing species perished, the rate of innovation almost matched that of the Cambrian. But the innovation was principally variations upon existing themes; no major new themes were added. In the Cambrian, by contrast, innovation was largely at the level of producing new themes, with variations upon them being relatively minor.' (1)

 
With many new predators now competing for the abundant supply of food on land (KFC has nothing compared to these times), a number of reptiles and a few mammal-like animals decided to return to the sea. However, those who were able to survive on land evolved into many different species to help increase their survival rate. (2)

Among the land-based creatures that successfully evolved at this time included the first true, hairy-like mammals and the first dinosaurs. But it would be the dinosaurs who would dominate life on the great supercontinent (known as Pangaea) for the next 170 million years.

Evidence to support the existence of this great supercontinent can be seen from the fossil evidence. The fossils show animals of the Triassic Period were widespread and remarkably alike throughout all the continents of the world. But later, after the supercontinent broke up during the Jurassic Period at around 210 million years ago, the animals diversified into more unique forms based on locality.

 
The Sun is known to take approximately 225 million years to travel one revolution around the Milky Way. Thus nearly one revolution around the galaxy ago, the Earth was just starting to be dominated by the great reptiles known as dinosaurs.

The early dinosaurs (the name comes from the two Greek words deinos, "terrible", and saurous, "lizard") were small creatures by our standards, but they later evolved and diversified into some of the largest land animals that ever lived. For more than 50 million years, huge plant-eating dinosaurs like the Brontosaurus, Briachiosaurus and Sauropods, and large terrifying meat-eaters such as the Tyrannosaurus Rex roamed the Earth.

This was a time when size did matter. Not only was there a plentiful supply of food on the great supercontinent to support very large dinosaurs on land - a kind of giant "smosgasbord" of fresh meat and vegetation just sitting out there ready for the taking, although competition for the food was still considered extremely fierce at this time - but also there was a survival bonus: the larger the animal can become, the more easier it is for the animal to survive the attack of most predators.

Despite size being an important factor in the survival of many dinosaurs, they had one major weakness: the reptiles did not develop a quick and effective internal body temperature-regulator. But this did not seem to worry the dinosaurs for there would be an extremely persistent period of very warm, moist tropical-like climate existent throughout much of the world for the next 50 million years.

Mammals, on the other hand, did develop a primitive internal body temperature-regulator and so were much better adapted to the lower temperatures existent at the extreme northern and southern latitudes on Earth, on mountain-tops, deep inside certain caves, or during the night where the great dinosaurs were probably more sluggish or the mammals could not be easily seen by the reptiles.

In fact, it would not have been too unusual for the mammals to come out at night to hunt and scavenge for food near the polar regions (or to take up residence high up in the tropical forests), while the dinosaurs kept themselves mainly to the warmer areas on the ground near the tropics and/or around lakes and shallow inland seas (which would have absorbed a lot of heat during the day).

Land-based mammals of this era were small creatures living secretly and did not evolve into larger more complex creatures until the great dinosaurs disappeared.

NOTE: Any large mammal of this era would have probably been wiped out due to the highly developed and powerful muscle structure of the two-legged carnivorous dinosaurs which gave these terrible lizards excellent speed (in a roughly straight line for the larger predators) to capture practically all large, cumbersome prey. (3)

 
The great supercontinent began to split apart.

Huge prehistoric forests comprising of cycads and conifers together with a thick undergrowth of ferns covering the ground were on the increase and dominated much of the great supercontinent. The evidence to support the size and abundance of these forests can be seen today from the presence of great coalfields in Europe, Australia and other parts of the world. (4)

 
A seaway separated the northern continent (North America, Europe and Asia) known as Laurasia, with the southern continent (South America, Africa, Australia, Antarctica, and India) known as Gondwana land. (5)

A team of Chinese and American scientists have discovered in the rich fossil beds of Yunnan province in China a 12mm long 195 million-year-old skull from a tiny animal no larger than a paper clip. What makes this prehistoric skull so remarkable is its bone structure. According to the scientists, this is the oldest known creature having the distinctive and crucial mammalian feature of having a one-boned jaw for better control of chewing and three middle-ear bones for improved hearing. Furthermore, the name given to this creature - Hadrocodium wui - means "full head" because of the skull's relatively large brain-holding capacity. Scientists believe a large brain did develop inside this skull because the animal utilised these distinctive anatomical features for its survival.

Zhe-Xi Luo, a member of the American team from the Carnegie Museum of Natural History in Pittsburgh, Pennsylvannia, said:

'Hadrocodium could be our distant cousin, an early mammal that existed alongside the ancestor of living mammals.' (6)

 
In the midst of the great dinosaur age at around 190 million years ago, the extraordinary abundance of plant life covering the great northern and southern supercontinents, as indicated by fossils dated to this period, gives evidence of a more moist and warmer climate than today. It was so warm that even polar ice caps may not have existed!

Scientists believe the origin of this supergreenhouse effect came from the great volcanoes dotted along major cracks in the Earth's crust caused by the breakup of the great supercontinents. Scientists say the great supercontinent of the south began to break-up and drift apart some 210 million years ago. This was the time when the mid-Atlantic ridge was born between 180 and 210 million years ago. By 160 million years ago, the air was laden with four to five times the carbon dioxide levels than existed just prior to the industrial revolution of the 1800s (or 2.5 times the quantity we see today due to humans burning fossil fuels).

The reason why the supercontinent had to break up around 210 million years ago is not precisely known. It is possible that another asteroid may have collided with the Earth (probably over water this time as there is no evidence to show there was a sudden reduction in worldwide temperatures for a brief moment which would have ended the great dinosaur age). Certainly it is known that another major and widespread extinction had occurred nearly 214 million years ago (8) coinciding at about the time of the great supercontinent breaking up. Or maybe it has to do with the way the strong internal heat currents in the magma of the Earth can break the crust into individual, free-moving tectonic plates. We can only speculate at the reason for the break-up of the great supercontinent.

At any rate, scientists are certain the weather of 160 million years ago was generally uniform and differences between summer and winter were not apparent. The temperatures at the poles rarely dipped below 10 to 15°C (7); whereas the levels of rainfall were very high, giving rise to more lush and denser tropical plant life across the great supercontinents. In fact, these wet conditions on land were made possible because of extensive plant life covering the supercontinents which in turn retained more moisture on the ground and provided sufficient humidity in the air to fall as rain along certain mountain ranges.

However, after the end of the Jurassic Period, nearly 136 million years ago, conditions began to get cooler. With fewer volcanoes and enough plant life absorbing carbon dioxide from the atmosphere together with some mountain-building and changes in the position of continents on the Earth's surface, we see for the first time in more than 50 million years how the Earth began to form polar ice caps.

Contradicting the traditional view that mammals at this time were small rodents scampering through the undergrowth searching for food and hiding from the dinosaur predators and weren't adventurous enough to diversify into other forms, a team of researchers from the Chinese Academy of Geological Sciences in Beijing and Carnegie Museum of Natural History in Pittsburgh headed by Dr Qiang Ji of Nanjing University reported in the 24 February 2006 journal Science the fossilized remains of a 60cm long platypus and Beaver-like mammal living 164 million years ago.

The well-preserved fossilized remains was found in 2004 in the inner Mongolian region of China known as Liaoning province.

Aptly named Castorocauda lutrasimilis meaning "beaver tail" (castoro is latin for "beaver" and cauda for "tail") and "like a river otter" (lutra stands for "river otter" and similis meaning "similar") by the discoverers, this interesting cat-sized creature is believed to be the largest known mammal living in the Jurassic period. It possesses limbs claimed to be well-developed for aquatic life including soft-tissue webbing in the hind feet as purportedly seen in the fossil. In fact, preservation of some soft tissue and fur imprints must be seen as a testament to the quality of the find compared to other fossils dated to this period. Scientists suspect the animal swarm in rivers and lakes like a platypus, and built nests in burrows along the shore. However its head looked more like a rodent with a broad scaly tail like a beaver, and its sharp teeth looked like an otter designed to eat fish and insects.

As Dr Zhe-Xi Luo, one of the discoverers of the fascinating creature and curator of vertebrate paleontology at Carnegie Museum of Natural History, said:

'Its lifestyle was probably very similar to the modern day platypus. It probably lived along river or lake banks. It doggy-paddled around, ate aquatic animals and insects, and burrowed tunnels for its nest.' (The Canberra Times: Platypus-like mammal fossil surfaces. 25 February 2006, p.18.)

The existence of this animal living in the watery environment has pushed back "the mammalian conquest of the waters by more than 100 million years" according to Dr Thomas Martin, an authority on early mammals at the Senckenberg Research Institute in Frankfurt, Germany.

 
In May 2005, palaeontologists in Utah, USA, claim they have found the missing link in a new species of dinosaur with feathers showing that around 125 million years ago some meat-eating reptiles slowly evolved into plant-eating types. The new feathered dinosaur species supporting this claim is called Falcarius utahensis. It literally means "sickle maker from Utah".

Standing not much taller than 1 metre and roughly 5 metres in length from head to tail, the near complete remains of Falcarius showed it had 10 cm long claws like sickles as commonly found in meat eaters. However the crucial link to herbivores was in the numerous small teeth lining its jaw. Instead of large, sharp pointy teeth to cut meat, the creatures entire teeth structure were more delicate and smaller to handle softer plant materials.

The possibility exists that this species, despite its sinister-looking carnivorous appearance, may have exclusively feasted on plants and nothing else. But no one knows for sure.

As Matthew Carrano, the curator of dinosaurs at the National Museum of Natural History (part of the Smithsonian Institution in Washington), said:

'It's the strangest looking dinosaur you can imagine.

'It's as if you sewed the dinosaur together from pieces of other dinosaurs.' (The Canberra Times: 'Patchwork' dino solves evolution puzzle. 7 May 2005, p.21.)

Could the evolutionary progression to plant-eaters (and of the feathers) be an indication that some animals were living in cooler areas frequented by fewer predators away from the oversized daily reptilian bloodbaths taking place daily in the hotter areas of the planet?

## UPDATE ##
23 November 2006
Like a giant genetic experiment going wild, another feathered dinosaur had four wings and another creature could do more than glide from one tree to another — it could flap its wings. A wealth of interesting fossils are now starting to emerge from China.

 
The planet Mars may have had conditions more favourable to the Earth at this time that it is today. Of course, whether life actually existed on Mars is still a matter of debate. Nevertheless it is believed that around 115 million years ago, conditions on the small planet would change drastically.

Mars is the fourth planet in distance from the Sun. It orbits the Sun in a rather unusual elliptical path — as if something may have collided with Mars a long time ago — such that it approaches Earth at its closest every 2 years and 2 months, reaching a point which is half as far away as it is at the farthest position.

This orange-red world rotates about its own inclined axis of 24.935º in 24 hours 37 minutes 23 seconds and has seasons similar to those on Earth except they are much longer due to the extended Martian year of 687.8 Earth days.

More interestingly is the atmosphere. Since Mars is a small planet, it has a low gravitational field. However, this is not the fundamental reason for the Martian atmosphere being feeble today with a pressure of only one-hundredth that on the Earth's surface. An analysis of the concentrations of certain types of isotopes of carbon, oxygen and nitrogen in the atmosphere suggest molecular nitrogen was in much greater quantities in the past than they are presently. This discovery has raised speculation that Mars may have once had a denser atmosphere consisting of mostly carbon dioxide, nitrogen and water, and the climate may have been warmer and wetter. Today, scientists are confident the atmosphere was much more humid, warmer and denser in the past.

The reason for the atmospheric chemical changes and loss in density is still not yet fully understood. But the best explanation so far is that a large asteroid collided with Mars where it penetrated deeply enough and at an angle to reduce the speed of the iron molten core of the planet. Suddenly the magnetic field to protect the planet from the energetic solar wind was suddenly weakened, resulting in the solar wind pushing away enough of the atmospheric gases to reduce the density. Finally the change in the chemical structure of the atmosphere was caused by the emissions of carbon dioxide and other gases from its interior through volcanic activity. If this is so, then Olympus Mons, a tremendously oversized Martian volcano and its other close neighbouring volcanoes on the Martian equator, may well be the remains of such a catastrophic event.

So far, scientists are placing the origins of Olympus Mons at around 115 million years ago. But the precise date is difficult to determine as the great volcanic mountain has, as recently as 2 million years ago, being spewing lava based on a calculation on the number of craters that have hit this region of the planet.

Otherwise if this was not a collision of any sort, then one must be inclined to follow the recommended timeline as published in the journal of Science dated 21 April 2006 for how Mars has changed. According to the article published in the journal, an international team of scientists headed by Jean-Pierre Bibring of France's Institute for Space Astrophysics claim if Mars was hospitable at some point in its history, it would have occurred not long after the planet's formation nearly 4.6 billion years ago. Another 600 million years later, a second era began whereby volcanic activity become the dominating feature of the planet. This is the period where it is believed the volcanic sulfur began to dry up the environment. The third and final era is marked by the formation of ferric oxides (the reddish material we see on the surface of Mars) not created or altered by water.

Although no life has ever been detected, according to the data received from experiments performed by the United States Viking landers, project scientist Gerald A. Soffen has still kept the question of extraterrestrial life on Mars open for speculation. He states:

'We have not visited the polar regions. I have always believed that in the search for life you must go where the water is. The permanent polar caps of Mars are frozen water and would act as a splendid "cold finger" to trap organic molecules. Who knows what those lucky future explorers of Mars will find there?'