Volcanism Theory - Dinosaur Extinction
Many researchers believe that a number of the same physical events would have occurred at the K-T boundary if either extensive volcanism or an asteroid impact took place. It is also believed that some biological results would be similar.
The volcanism and asteroid impact theories are equally weak in their biological prediction. The major difference with these two theories is in their timing.
The asteroid impact theory measures most of the cataclysmic effects in months or years, with residual physical effects lasting possibly hundreds or a few thousand years, the volcanism theory measures effects into the millions of years.
500 000 years before the K-T boundary and 200 000 years before the asteroid impact massive volcanic activity began in India. A flood basalt eruptions produced millions of cubic miles of new rock over hundreds or thousands of years resulting in what is now know as the "Deccan Traps".
The Deccan Traps could have caused extinction by the release of dust and volcanic material into the atmosphere blocking sunlight and thereby reducing photosynthesis.
This massive volcanic activity exerted pressure in the biosphere causing the gradual downfall of the dinosaurs and other cretaceous creatures. It is argued that the Chicxulub impact was one of the many impact hits the earth took during this time period.
It is believed that a second impact or possibly more which is often refereed as the KT impact, was larger than the Chicxulub impact, was the final event that pushed the dinosaurs into extinction and produced the iridium layer.
The second impact's location has yet to be discovered, but tentative evidence points to somewhere in the Indian Ocean. This second asteroid impact also contributed to the extinction of the Cretaceous Period.