THE "KELLER HYPOTHESIS"
Recently, Dr. Gerta Keller and her team at Princeton proved quite conclusively that the Chicxulub crater predates the Cretaceous-Tertiary boundary by about 300,000. She challenges the notion that the Chicxulub crater was impact that killed off life 65 Ma.
Dr. Keller believes the K/T extinction was caused by multiple impacts, volcanism and climatic changes. The Chicxulub impact, 300,000 years before the boundary, stressed the ecosystems on Earth causing species numbers to be reduced. Another impact at the K/T boundary (the one synonymous with the iridium anomaly) coupled with the volcanism in India further accentuated the loss of species. These events combined caused an enormous amount of change to the climate which adversely affected the biota at the end of the Cretaceous, effectively driving them to extinct in large numbers.
This theory explains why there was a decline in species before the boundary. Another important factor regarding the theory, it explains several of the phenomenon attributed to the extinction. For more information on Dr. Keller's work, click here.