User:Tborges13/Alvarez hypothesis

Criticism
Despite the fact that the Alvarez hypothesis has overwhelming support from the scientific community, Keller has continued to push for research to weaken its credibility. The Deccan Traps theory was first proposed in 1978 by geologist Dewey McLean but quickly lost traction. The Deccan Traps are an area of volcanic flood basalts in Western India spanning ~1.3 square kilometers that were created by massive volcanic activity during the same time period in which the Chicxulub impact occured. Prior to Keller's research, the timeframe of the Deccan Traps' eruptions had a significantly large range of error, making it difficult to draw strong conclusions regarding their connection to the K-Pg extinction. In a 2014 report, Keller and her colleagues used uranium-lead zircon geochronology to more accurately identify the eruptions as occurring both within a span of one million years and around 250,000 years prior to the K-Pg boundary. Keller additionally determined that ocean temperatures rose seven to nine degrees Celsius during the most significant period of the Deccan eruptions. Along with ocean acidification, ozone reduction, acid rain, and a release of harmful gases, she asserts that these conditions were sufficient to have initiated the mass extinction.

Keller has specifically rejected the Alvarez hypothesis, pointing to evidence she gathered from the Chicxulub crater in 2009 revealing that twenty inches of sediment separates the impact from the extinction. The finding suggests that the impact occurred 200,000 to 300,000 years before the K-Pg extinction, a period far too large for the two to be correlated. This, however, contrasts the range of 33,000 years determined by Paul Renne in 2015, as well the more recent assertion that a tsunami generated by the impact created the unusual sediment layer. Keller additionally claims that the impact did not cause as much ecological damage as is widely believed, and she determined that many foraminifera species began to decline well before the impact event occured. Her 2009 project revealed that the 52 species found in the sediment prior to the impact were present in the sediment following it, suggesting that the impact caused minimal extinction.

A more recent theory combining both Deccan volcanism and the impact hypothesis has been developed by teams at UC Berkeley lead by Paul Renne and Mark Richards. This theory proposes that the impact itself instigated the most intense period of Deccan eruptions, both of which had devastating effects contributing to the K-Pg extinction. Renne and Richards calculated that the Chixculub impact was capable of producing seismic activity strong enough to intitiate volcanic eruptions. They determined that the largest period of Deccan volcanic eruptions, or the Wai subgroup, occurred 50,000 to 100,000 years after the Chixculub impact, which is consistent with theoretical predictions modeling the length of time after which eruptions should occur. The group also confirmed that the length of time between the extinction and subsequent biological recovery was consistent with the length of Deccan volcanic activity, proposing that the eruptions paused the recovery of the marine ecosystems destroyed by the impact.

Debate regarding the cause of the K-Pg extinction has proven to be extremely controversial among researchers, and the resilience of its intensity has earned it the moniker of the "dinosaur wars." Criticism is unusually harsh, targeting not only research findings but the credibility and integrity of the scientists themselves. Verbal accusations have been thrown both by and toward many prominent researchers including Gerta Keller and Luis Alvarez, discouraging civil debate and in some cases threatening careers. Given his role in developing the Alvarez hypothesis, it is noteworthy that Walter Alvarez is an active member of the UC Berkeley team researching the connection between Deccan volcanism and the Chicxulub impact.