THE BEGINNING OF THE MESOZOIC: INTEGRATING 70 MILLION YEARS OF ENVIRONMENTAL STRESS AND EXTINCTION

Much of the work to date on the effects of extinction during the early Mesozoic has concentrated on the brief time intervals when there are mass extinctions. In large part these mass extinctions have been treated exclusively with little attempt to investigate how the broader events of this time helped shape these mass extinctions and their impact on life.

Indeed, the Mesozoic began at about 251 mya with the greatest mass extinction that animal life has experienced on Earth. However, the effects of this lingered for millions of years into the Triassic. Life returned to “normal” later in the Triassic, only to suffer new crises in a variety of environments through the early part of the succeeding Jurassic period. This 70 million year interval of heightened environmental stress and biotic crisis may have been due to the same underlying cause. The root mechanism is very likely that this was the time of the early breakup of the supercontinent Pangea with formation by mantle plumes of three huge continental flood basalt provinces (Siberian Traps, CAMP, Karoo-Ferrar Traps). This led to stressful environmental conditions causing the long interval of biotic crises and extinction that characterized the beginning of the Mesozoic, and which may ultimately be why there are overall high extinction rates for the Triassic (Bambach and Knoll, 2001).

Superimposed upon these long-term stressful intervals were short-term punctuations of environmental stress that caused the three early Mesozoic mass extinctions (end-Permian, end-Triassic, early Toarcian). Causes of these mass extinctions might have been coupled with the instigator of long-term stress, beginning with extremely intense periods of flood basalt volcanism, that could have led to a potential cascade of unusually stressful tectonic, oceanographic and climatic effects. If extraterrestrial impact were the cause of one or more of the early Mesozoic mass extinctions, it is likely that the already stressed environments of much of the early Mesozoic “set the table” for the Earth’s biota to enter a phase of mass extinction.

This long period of environmental and biotic stress during the early breakup of Pangea represents a crucial time in the evolution of life on Earth, because survivors of this time founded much of the seafood that characterizes today’s oceans.