It is generally believed that 65 million years ago the dinosaurs became extinct when a massive comet or asteroid collided with the earth, thus putting an end to one of the most successful orders of life that ever existed on planet Earth.
Scientific research shows that many and varied species of dinosaurs had lived and died beginning about 230 million years ago, during the geologic period of earth's history known as the Triassic, and continuing on throughout the following Jurassic, and Cretaceous periods, a time-span of about 165 million years.
Dinosaurs were the dominant land animals of their time, populating many regions of the earth, providing today, a worldwide source of their fossil remains. It is acknowledged that although the dinosaurs are extinct, there is a close anatomical relationship between birds and dinosaurs, which supports the opinion of many paleontologists that birds may have evolved from dinosaurs, perhaps from the small dinosaurs of the late Jurassic. Possible evidence of this includes the three-toed feet and the air filled bones and the wishbones found in the many thousands of today's bird species.
The dinosaurs appeared, evolved, and eventually disappeared millions of years before human beings appeared on earth. Huge fossilized dinosaur bones have been discovered and excavated, providing dramatic displays, when reassembled, for museums. And dinosaurs are frequently depicted as being massive in size, bigger that elephants and often as ferocious meat eaters, such as the Tyrannosaurus Rex may have been. But in reality they were an extremely varied group of creatures with species of many sizes some as small as the common Dogs kept as pets today.
The cause of their extinction has long been a mystery and the subject of conjecture and debate, with the two main currently popular theories centered around some form of catastrophe to account for their apparently rather sudden disappearance, sudden in geological terms perhaps but not actually in an instant. In fact it is possible that long before the time-line of 65 million years ago there had already been a gradual and significant dying out of many dinosaur species and the final catastrophic event could merely have delivered the final blow.
The catastrophes, were they earthly or from outer space?
Was it the impact of a solar system body from outer space or extensive volcanic outpourings on earth over millions of years that caused the demise of the dinosaurs? Actually, we have evidence of both occurring in that time period but as yet there is not a consensus among the scientific community that confirms one or the other, or both, as the cause of the extinction, although currently, most support appears to be on the side of the impact theory.
One likely catastrophic event may have been the impact of a large asteroid or comet from outer space, where many such objects constantly revolve in the solar system and occasionally enter a collision path with the earth or other planets. And supporters of this argument have found the evidence and extent of such an extra-terrestrial body in the impact crater, known as the Chicxulub Crater in Mexico's Yucatan Peninsula.
But long before the impact crater was searched for and finally found, Walter Alvarez, an American geologist, working in Gubbio, Italy, identified an unexpected mineral in the rocks there, called iridium. Iridium, when found in the earth's surface rocks, usually occurs as only a minute percentage of the total material in situ but in the case of the Gubbio iridium, where it existed between the boundary layers of the underlying Cretaceous and overlying Tertiary rocks, it was in much greater percentages than normal. The 65 million year old boundary layer marks the close of the age of the dinosaurs - and of a multitude of extinctions of other land and sea creatures, a time often referred to as "the Great Dying".
It was known that concentrations of iridium similar to those occurring at Gubbio were common in meteorites arriving on earth from outer space. Based on this, Walter Alvarez, together with his colleagues and including his distinguished Nobel prize-winning father, Luis Alvarez, suggested this was evidence that firmly established that an asteroid or comet had impacted the earth and created the conditions that resulted in the demise of the dinosaurs and other fauna and flora that disappeared from the earth 65 million years ago.
With the subsequent finding and dating of the Chicxulub Crater, mentioned above, the culprit was identified in the opinion of the impact supporters.
But there are dissenting voices. Paleontologist Gerta Keller of Princeton University has carried out extensive fieldwork at Chicxulub together with a team of other distinguished scientists and claims that their investigations show that the age of the crater is 300,000 years older than the accepted extinction event and that there is no evidence whatsoever of extinction of life forms during that following 300,000 years. Keller is also a supporter of the volcanic outpourings, mentioned below, as a major contributing cause of the mass extinction.
But, in turn, many scientists disagree with Keller's analysis, contending that the 10 feet of material representing the 300,000 years without extinct life, that they claim is misleading her, was caused by tsunami activity that occurred as a result of the impact.
Whoever is right, the iridium anomaly points to an impact having occurred so if it wasn't Chicxulub what was it? There are several other major impact sites that are now known to be of the right age, so it is possible that there were a series of associated impact events, perhaps all being fragments of a much larger celestial body that may have broken apart through its own collision in space. To support this theory, there are craters in the Ukraine, in the North Sea, and a very large possible crater, yet to be absolutely confirmed as such, existing off the west coast of India. And there could have been other craters now erased by erosion or even by the gradually moving continental land masses as they react to the tectonic forces that slowly repositions portions of the surface of the earth's crust.
To add to the chain of coinciding events, it is possible that the crater off the coast of India, called the Shiva Crater, had a double effect, allied to the two main theories for the extinctions. In one case as an impact event similar to Chicxulub and in the second case as a major contributing cause worsening the already occurring volcanic events of the Deccan Traps of what is now India, mentioned below.
Recently, professor Sankar Chatterjee of the University of Texas, announced at the 2009 Annual Meeting of the Geological Society of America in Portland, Oregon, research findings and a theory regarding the Shiva Crater, the world's largest known crater.
The new theory suggests that the source of the 25 mile wide Shiva Crater, a meteorite, came to earth 300,000 years after the Chicxulub crater was formed - is this also a confirmation of Gerta Keller's work?
Volcanic outpourings of the Deccan Traps of India
Another possible cause of the extinctions of the Great Dying are the million years of constant outpouring of volcanic lavas that is known to have occurred before and during the time of the extinctions. These are known as the Deccan Traps. Such extreme volcanic activity would have had dire climatic consequences world wide, sufficient to have caused the extinction of not only the dinosaurs but the multitude of species that are known to have become extinct at the same time as the dinosaurs. The loss of plants that would have also occurred due to the climate disruptions would have been disastrous for the many dinosaur species that were vegetarians.
There have been several similar mass extinctions over the earth's long history, and researchers say that most of those were accompanied by long periods of volcanic activity the same as that of the Deccan Traps of India. The volcanism that formed the Deccan Traps being considered as the cause of the mass extinctions has great support among those working in the field. In their opinion, their own extensive investigations provide convincing evidence in support of the volcanism theory and they believe that the mass extinction would have occurred because of them even if the impacts had not also happened during that time.
So opinions remain divided, while Walter Alvarez and others retain their views that Chicxulub is the culprit, other geologists believe otherwise, suggesting a hypothesis linking other evidence including climate change, significant volcanic eruptions or perhaps a combination of all of them that occurred 65 million years ago.
But questions remain to be answered. For instance, why did some species of creatures, such as crocodiles, frogs, and birds, survive while others did not?
Perhaps not all dinosaurs became extinct
It seems that some dinosaur species may have outlived the Great Dying. That is according to a May 1, 2009 report in The National Geographic News describing findings and conclusions of James Fasset, a scientist from the US Geological Survey in Sante Fe, New Mexico. Fasset's discoveries in the Western United States convince him that some dinosaur species survived beyond the mass extinction for as long as half a million years and the evidence to support that, he believes, is unequivocal.
However, while not ruling out the possibility, other paleontologists are not yet ready to accept Fasset's evidence and opinions.
Research continues and we shall await results with interest.
Jim Robinson, the author of this article has also written for e-zine on several popular science and cultural subjects. And also on diabetes related topics.
Being himself a diabetic, his diabetes website discusses the steps in menu planning and weight loss, exercise and other topics of importance to fellow diabetics. If you are a diabetic, worth a visit, check it out!
