The extinction of non-avian dinosaurs happened all of a sudden about 65 million years ago. Later on, other animals also became extinct. This included the Mosasaurs, Ammonites, Pterosaurs, Plesiosaurs, crocodiles, herbivorous turtles, some birds and various other mammal groups. This mass extinction event became referred to as the Creceous-Tertiary Extinction Event.



For years, many scientists, and paleontologists extensively studied this event to fully understand the root cause of this mass extinction. They came up with two basic theories to explain the phenomenon.

Theory of Asteroid Collision

It was the late Walter Alvarez and his colleagues who brought up this theory in the year 1980. He theorized the extinction event happened in the latter part of the Cretaceous period due to a so-called “Bolide Impact.” Evidence about this event was linked to the sudden increase of iridium levels. It was suggested that a 5 to 15 kilometer wide bolide actually hit the Yucatan Peninsula, forming a 170 kilometer wide Chicxulub Crater.

Scientists have yet to prove if the dinosaurs were declining or thriving prior to the Asteroid Collision Event. Other scientists propose that it was a meteorite that caused the unnatural and long drop in the atmospheric temperatures of the earth. Still, there are those claiming that it created a bizarre heat wave instead.

Even if the extinction speed cannot be presumed from the fossil records alone, other models suggest that it was an exceptionally rapid extinction event. In fact, scientists arrived at a consensus that this impact caused extinctions indirectly and directly. The indirect root would be from the worldwide cooling effect. Matter ejected from the noted impact crater presumably reflected the sun's thermal radiation. The direct root, on the other hand, was brought about by the meteorite impact's heat waves.

Last September 2007, newer findings from Southwest Research Institute's William Bottke of Boulder, Colorado, as well as Czech scientists have reportedly identified the probable source of this Chicxulub Impact. They were able to calculate that Baptistina, a giant asteroid that orbits the Jupiter and Mars' asteroid belt, was struck 160 millions of years ago by an unnamed and smaller asteroid. This impact crushed Baptistina, forming a cluster still existent up to now as the “Baptistina Family.” Further calculations indicated that a few fragments went hustling into the earth-crossing orbits such as the wide meteorite that struck the Yucatan Peninsula of Mexico, creating this Chicxulub Crater.

Deccan Traps Theory

Prior to year 2000, there have been arguments about the “Deccan Traps flood basalts” which caused the mass extinction of dinosaurs and other animal groups. With this theory, however, extinction was projected as gradual. This is since this flood basalt event was estimated to have begun about 68 million years ago, lasting for more than two million years.

Since other pieces of evidence showed that about 2/3 of these “Deccan Traps” were actually created just a million years back, it was assumed that the eruptions triggered a rapid extinction event. Thus, it still took some time before the total extinction of dinosaurs took place as compared to the Asteroid Collision Theory.

These Deccan Traps may have caused the mass extinction via several mechanisms. This includes the release of sulfuric aerosols and dust in the air, blocking the sunlight and affecting photosynthesis processes in plants. When it comes to volcanism effects, this resulted to emissions of carbon dioxide which probably increased the greenhouse effect after the aerosols and dust cleared the atmosphere. Furthermore, prior to this mass extinction, actual releases of volcanic gasses were linked to have contributed to massive global warming.

Theory of Asteroid Collision versus Deccan Traps Theory

With the Deccan Traps Theory projecting a much slower extinction process, Luis Alvarez pointed out that this is a misleading theory brought about by sparse data. Although his assumptions were not well received then, further studies on fossil beds have given some weight on his claim. Later on, paleontologists started accepting the fact that this mass extinction was due to the massive impact on the earth.

However, even the late Walter Alvarez admitted that there were already several major changes happening on earth prior to this impact. This included the catastrophic volcanic eruptions and drops in the sea level, producing these Indian Deccan Traps.