This is a picture of a recently discovered bird-like dinosaur that was discovered in China during late 2007. One of the greatest mysteries of all, besides the origin of the universe, is how the dinosaurs became extinct after ruling our planet for millions of years. There are several viable theories...
A Chinese geo-scientist, Chaoqun Yang, claims that massive climatic and geological changes, due to earthquakes and volcanic eruptions towards the end of the Cretaceous Period, resulted in the terminal infertility of male dinosaurs. His theory has been accepted by a number of renowned geologists and paleontologists in China's Guangzhou province. Dr. Yang's theory is based on the fact that many well-preserved dinosaur egg fossils, found in the Xixia basin in central Henan province, far outnumber fossils of fully grown dinosaurs. He believes that dry weather during the Cretaceous Period caused water levels in lakes to drop, leading to higher concentrations of salt and minerals in the water. The large amounts of minerals, especially sulphates, damaged the reproductive systems of dinosaurs that drank from the lakes. In addition, these drastic temperature and climate changes, led to a build up of heat thereby causing a pre-mankind greenhouse effect. This greenhouse effect could have eventually caused dinosaurs to become sterile and unable to reproduce. The main problem with this theory is that it does not explain the survival of the smaller mammals and other species. This also does not explain the rapid extinction of dinosaurs as this idea would take a long period of time.
Another theory offers that during the age of dinosaurs, gravitation on Earth was lighter than today. Hence, all objects and living things were lighter. 65 millions years ago, suddenly, the gravitation increased. Dinosaurs became too heavy and as they were unable to adapt, they died. Mammals, powerful and agile in spite of their smaller size, survived. Reptiles survived also because they appeared during a time gravitation was more important than during the Dinosaurs' age. Birds survived because the augmentation of gravitation made the atmosphere more heavy - as a paradox it was easier for birds to fly. Major problem with this theory is the "gravitational constant" put forth by Sir Isaac Newton, which determines that gravitational pull does not change.
Next, is the "Stress on Thin Eggshell Theory." This theory can be largely attributed to Dr. Heinrich K. Erben of Bonn University in Germany. His research led him to the conclusion that a species of dinosaur procreated a shell that, through time, grew progressively thinner. Dr. Erben reasoned that luxurious swamps and warm climate activity led to "Biological Prosperity". These two factors contributed to problems such as over-population, over-feeding and other such related stresses. Assuming the relationship between birds and dinosaurs is accurate, Dr. Erben showed that modern birds, raised under similar stresses, create a hormonal imbalance. This hormonal imbalance could have increased estrogen output in female dinosaurs. This would result in thin eggshells, thus the extinction of the species. A major flaw that this theory suffers is why only certain species were affected and others weren't.
There is also the "Ozone Depletion Theory." Dr. Keith, professor of geo-chemistry at Pennsylvania State University, developed this theory based on the geological record that shows large areas of volcanic activity. Large amounts of volcanic gases could have depleted the upper atmospheres protective ozone layer. Flesh-skinned creatures such as dinosaurs would have been vulnerable to the ultraviolet radiation now bathing the Earth. Furry mammals, feathered birds and select sea creatures would have had enough protection to account for their survival.
The "Artic Ocean Spillover Theory", developed by Stefan Gartner and James P. McGuirk of Texas A&M University, suggests for a brief time the ocean surface waters became cooler, not warmer. During the Mesozoic, continental drift would have caused the Arctic Ocean to have become isolated. Salt-water or fresh-water would result from such an event. Colder, lighter arctic water would have mixed with the much warmer Atlantic, forming a frigid layer on top of the heavier salty sea-water. A rapid drop in world temperatures - as much as 10 degrees Celsius, would have resulted. Once this happened, a devastating chill would have spread over much of the world - perhaps ushering in a "quick ice-age." However, no evidence supports the idea of the Arctic Ocean ever being fresh or salty.
The "Magnetic Reversals Theory" offers the fact that the Earth's magnetic field, like the ozone layer, acts as a barrier against outside forces. Periodically, our Earth's magnetic field changes polarity (north becomes south, south becomes north). It is possible this would have had an effect on the reproduction ability of dinosaurs. While not a new theory, this is still under development.
Finally, there is the "Impact Theory" where a large asteroid, comet or other space debris, collided with the Earth. What evidence would you need to suggest a giant object crashed into the Earth and caused the extinction of an entire species? First you would need to find a large enough crater on Earth and date it back to the time of the great extinction. The Chicxulub Crater, located in the Gulf of Mexico, has been dated back to 65 million years ago and is over 10 kilometers in diameter. Tektites and stishovites, rocks that are made from great heat and pressure, have been found to be around 65 million years old and they are most likely caused by a cosmic collision. The evidence of an impact is there, but how did this cause the extinction of the dinosaurs? Dr. Louis Alvarez developed the theory of a "volcanic winter" causing the demise of the dinosaurs. When the asteroid crashed into the Earth, a huge amount of dust was thrown into the atmosphere, thereby blocking out the sun's rays. This would stop all photosynthesis causing the death of most of the plant life, meaning death for the herbivores due to lack of food. This would in turn devastate the carnivores in the food chain. In addition, the temperature would drop and extinction would not only be determined by the dinosaurs' eating habits, but it would affect them all the same. In the best scenario, the temperature drop would just slow the dinosaur down, preventing it from getting enough food. In addition, when the asteroid crashed into the Earth, there were other devastating effects, but they did not last as long. The first blast waves would eradicate everything in their paths. Tsunamis would occur all over the world, flooding vast amounts of land. Massive earthquakes would occur all over the Earth and volcanic activity would abound. The power of the impact would cause global wildfires and would evaporate water in rock. These first effects would wipe out a large percentage of the dinosaur population. Those that survived these first effects, would not have lived through the volcanic winter. The various birds and small mammals that survived clung on to the little viable food and water that was left until the Earth replenished itself when the atmosphere cleared. This is the most widely accepted theory today.
Something to think about: we know for a fact, beyond any reasonable doubt, that our planet has witnessed several mass extinctions. It has been theorized that these mass extinctions take place when Earth can no longer support the amount of life feeding off of its resources. With mankind's exploding population and our endless use of our natural resources, are we so bold as to think it cannot happen again?