Not By Asteroid Alone: Rethinking the Cretaceous Mass Extinction
At the end of the Cretaceous period some 65 million years ago, an asteroid slammed into Mexico’s Yucatan Peninsula, causing severe but selective extinction. While that is widely accepted, it has remained unclear exactly what the mechanisms were that caused extinction of ocean-dwelling organisms. Proposed explanations include global darkness due to blocking of sunlight with resulting interruption of photosynthesis at the base of the food chain, deadly radiation due to ozone destruction, global cooling or warming, and ocean acidification). Various widely-accepted hypotheses focus on a collapse of the primary and export productivity in the oceans – such as the so-called Strangelove Ocean or Living Ocean hypotheses, respectively – but do not account for the finding that deep-sea floor dwelling phytoplankton-dependent benthic foraminifera did not undergo significant extinction. Recently, however, research conducted at Universidad Zaragoza in Spain concluded that decreased productivity was moderate, regional, and insufficient to explain marine mass extinction, suggesting instead that a temporary period of increased surface ocean acidity may have been the primary cause of extinction of calcifying plankton and ammonites, with recovery of primary productivity possibly being as fast in the oceans as on land.