The work, done by Gregory Retallack, professor of geologic sciences at Oregon, involved a worldwide compilation of thousands of exceptionally well preserved fossil assemblages of fish, crustaceans, insects, starfish and other life forms. There are only about 41 episodes of exceptional preservation from the last 500 million years, and each episode is widely distributed around the world.
Well known examples of such preservation of complete soft-bodied fish and other creatures include the Burgess Shale (dating to the Middle Cambrian Period of about 508 million years ago and found near Field, British Columbia) and the Solnhofen Plattenkalk (dating to the Late Jurassic Period of about 150 million years ago and found in Bavaria, Germany). Such exceptional assemblages were thought to have been preserved in environments that were unusually low in oxygen, highly saline, very cold, or extremely dry. What was not suspected until the new compilation was the global distribution of other exceptional fossil deposits of the same ages. Independent estimates of atmospheric pollution crises come from studies of carbon anomalies, microscopic pores of fossil leaves and climatic indicators from fossil soils. Methane outbursts from volcanically intruded coals and submarine gas hydrates are prime suspects for these lethal atmospheric pollution events.
"Lowered levels of oxygen can kill fish and other creatures in marginally aerated environments, and also preserve their carcasses from dismemberment and decay," said Retallack. "Data from carbon anomalies and microscopic leaf pores indicate that some of these killer greenhouses ramped up, within only a few thousand years, to intolerable levels of more than 10 times the modern level of atmospheric carbon dioxide. What stopped them from continuing on to a sterile greenhouse atmosphere like that of Venus? It was the widespread death and burial of animals and their carbon which created fossil bonanzas, the likes of which may have saved us from the heat sterilization experienced by our sister planet."