190 to 195 MILLION YEARS AGO
As the Jurassic Period began, the world saw the spread of extensive forests dominated by cycads, conifers, and ferns, which thrived in the warm, humid conditions that followed the Late Triassic extinction event. While coal deposits do provide evidence of ancient forest abundance (4), the largest coal‑forming periods occurred earlier in the Paleozoic; however, Jurassic vegetation was still widespread and lush, supporting diverse ecosystems across the newly separating continents.
Speaking of separate continents, 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)
Also worth mentioning at this time is the work of a team of Chinese and American scientists who 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)
NOTE: Mammals with a womb to carry its offspring, as opposed to laying eggs in the environment or having a pouch to carry the offsprings, first appeared 165 million years ago.
190 to 136 MILLION YEARS AGO
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! If there was ever a good time to have global warming, this would be it. At least the plants would have provided adequate shade and retain enough moisture on the ground, while providing reasonable amounts of food to any animals that depended on them. Perhaps a lesson to be learned here for humans of more modern times.
Scientists believe the origin of this super-greenhouse effect came from the great volcanoes dotted along major cracks in the Earth's crust caused by the breakup of the great supercontinent. Scientists gave an estimate on the breakup of the great supercontinent of the south at around 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 primarily to humans burning fossil fuels, but in the Jurassic period we can thank volcanism for this).
Another suggested reason for global warming at this time could be related to certain types of insects and the high populations they may have reached. For example, the number of termites may have reached plague proportions to the point where the methane they emit together with the greater rate of decomposition of trees by these insects (and from fungi) leading to emission of carbon dioxide could see enough of these greenhouse gases increase global temperatures. One estimate has it that termites can contribute as much as 11 per cent to global warming, and probably higher at the time of the dinosaurs living in the rainforests. To support this view, biologist Joshua King from the University of Central Florida, and Mark A. Bradford, an assistant professor of terrestrial ecosystem ecology at the Yale School of Forestry and Environmental Studies conducted a study on the decomposition rate of plant materials in the presence of fungi and termites and compared this to temperature alone. During the study, samples of wood material were subjected to different but consistent temperatures in two geographical locations and compared the results with the effects of termite and fungi activity. According to the analysis, local factors (i.e., termites and fungi) explained about 75 per cent of the variation in wood decomposition compared to 25 per cent on climate. As Bradford said:
"We've reaching the wrong conclusion about the major controls on decomposition because of the way we've traditionally collected."
Further details of this study can be found in Nature under the title "Climate fails to predict wood decomposition at regional scales", 1 June 2014, available from here.
As a result of the warmer conditions, the polar regions were likely lacking in ice sheets during this time. This means the temperature differential between polar and equatorial regions was minimal, leading to a diminishing of ocean currents. Along some coastal regions near nutrient-rich waters entering the ocean and seas from rivers, algae blooms would increase to toxic levels. When the algae blooms die and sink into the water, its decomposition leads to rapid oxygen depletion. Without this circulation in the ocean, deep waters stopped receiving oxygen-rich surface water. The oceans stagnate and eventually mass deaths of marine life begin. Today, scientists are certain at least one such Oceanic Anoxic Event (OAE) of this kind occurred around 183 million years ago. But it would not be the last time such an event would happen.
As for why the supercontinent had to break up around 210 million years ago, this 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 could 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.
Whatever contributed and had maintained global warming for such a long time (probably starting with the Permian asteroid impact), scientists are certain the weather of 160 million years ago was generally uniform and differences between summer and winter were not apparent. 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, these extremely warm conditions were about to change.
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, as well as possible changes to the soil chemistry (e.g., less phosphorus to promote the growth of large plants) we see for the first time in more than 50 million years how the Earth began to form polar ice caps, especially by around 125 million years ago. But apparently, this cooling down effect would not last long, as we will see in the Cretaceous period.
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 hybrid mammal that lived around 164 million years ago. The well-preserved fossilized remains were 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 possessed 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 swam 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.
125 MILLION YEARS AGO
In May 2005, palaeontologists in Utah, USA, claim that 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. Therefore, there is the possibility that this species—despite its sinister-looking carnivorous appearance—may have feasted exclusively on plants and nothing else. But, of course, 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 in the hotter areas of the planet?
UPDATE
23 November 2006
Like a giant genetic experiment gone 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.
UPDATE
9 June 2014
China is certainly coming up with its fair share of extraordinarily well-preserved and original fossil finds in recent times to make many paleontologists green with envy. The discovery of a flying pterosaur representing a new genus and species known as Hamipterus tianshanensis is certainly no exception. In fact, on closer examination, the eggs themselves (no less than 40 in total) were described by field researcher Wang Youlin as "three-dimensionally [preserved].", together with the parents. Xiaolin Wang of the Chinese Academy of Sciences gave more details of the find when he said:
"Five eggs are three-dimensionally preserved, and some are really complete. It was most exciting to find many male and female pterosaurs and their eggs preserved together."
Scientists have observed how the eggs had a pliable and thin shell on the outside and a soft, thick membrane inside, reminiscent of those found in snakes today. The eggs appeared to have been buried in sandy areas along the edge of an ancient lake mainly for protection from most predators, but also to provide enough moisture to prevent the eggs from drying out. As the eggs were developing and for a short period after the offsprings emerged from the eggs, either the female or male (or perhaps both) parents would come down to regulate the temperature in the sand during the day and to provide some further physical protection to the youngsters from the many small marauding predators roaming the area, especially from the forest nearby, and at night the parents would simply come down and rest on the ground as a large colony. Unfortunately, during a particularly brutal storm that swept over the area about 120 million years ago, it seems a number of these dinosaurs had died. And with no protection from the hot sun the following day, the young animals inside the eggs died as well.
Looking at the well-preserved and complete fossils of the parents and their numbers (so far dozens have been uncovered and more are expected), scientists have been able to provide some remarkable details into the life, gender and general appearance of these somewhat gregarious creatures. What we do know so far is that these dinosaurs loved to stay together in colonies near the shore of a large prehistoric lake. Depending on their age, the wingspan varied between 12 centimetres (for the youngsters) to 25 metres (for the parents) from tip-to-tip, or roughly the length of a tennis court would pretty much give a good indication of the maximum length when the wings are stretched out. There are also clearly distinguishing features between the genders with the male possessing a noticeable and potentially colourful head crest.
As the researchers wrote in their article titled "Sexually Dimorphic Tridimensionally Preserved Pterosaurs and Their Eggs from China" (published in Current Biology on 5 June 2014):
"Sites like the one reported here provide further evidence regarding the behaviour and biology of this amazing group of flying reptiles that has no parallel in modern time."
So expect more information to come about these interesting creatures very soon.
The fossilised skeletons and eggs were first unearthed in 2005 in the Turpan-Hami Basin, south of the Tian Shan Mountains in Xinjiang, northwest of China.
115 MILLION YEARS AGO
The planet Mars may have had conditions more favourable to the Earth at this time than we see 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 started to 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. We also know that 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 remnants 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 thus making it difficult for scientists to calculate the number of craters that have hit this region of the planet at the present time.
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 that 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 been detected so far, 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?"