Earth's past is warning for the future
When the Earth鈥檚 carbon dioxide level increased at a rapid rate during the Triassic-Jurassic period 200 million years ago, nearly half the ocean鈥檚 marine life became extinct. USC Dornsife geologists contributed to a recent paper that examines materials embedded in ancient rocks to provide clues about the possibility of similar future global events.
The study published in the March 2 issue of Science indicates that ocean acidification may have been the cause of extinction events in the past, and warns of future extinctions because an even more severe acidification event is happening today.
USC Dornsife alumna Sarah Greene, who earned a Ph.D. in geological studies in 2011, and Rowan Martindale, a doctoral candidate in earth sciences, joined scientists from 18 institutions worldwide in researching geological records. The evidence suggests what the future holds if atmospheric human-induced carbon dioxide levels continue to increase.
Greene and Martindale along with 19 other scientists report that examining the fossil records of ancient acidification events may provide scholars with evidence to predict and plan for future global changes. B盲rbel H枚nisch of Columbia University was the paper鈥檚 lead researcher.
Martindale and Greene have scoured ancient rock beds in Austria, England, British Colombia and Nevada for evidence of acidification.
鈥淭he Triassic-Jurassic event tells us that carbon dioxide increase coupled with a hypothesized acidification event caused a mass extinction,鈥� Martindale said. 鈥淭hat may tell us what organisms will die or survive in the near future and how long it will take for things to recover, if they do recover.鈥�
The study discusses how carbon dioxide emissions affect marine life. When gases are emitted, carbon dioxide in the atmosphere is absorbed into Earth鈥檚 oceans. When carbon dioxide and water bind together to create carbonic acid, the ocean becomes more acidic and water pH levels decrease; an event known as ocean acidification. The average ocean pH has decreased from 8.2 to 8.1 since the late 18th century industrial revolution and may decrease by additional 0.2 to 0.3 pH units by the end of this century, Martindale said.
David Bottjer, chair of USC Dornsife鈥檚 Department of Earth Sciences and professor of earth sciences and biological sciences, ignited Martindale鈥檚 interest in the Triassic-Jurassic period during her first year at USC by recommending she combine her interest in reef ecosystems with mass extinctions. Since 2007, she has researched evidence of elevated atmospheric carbon dioxide levels to determine the chemistry behind ocean acidification in order to understand effects on ecosystems.
鈥淭he contribution made by Rowan and Sarah to this paper is crucial to the study鈥檚 success,鈥� Bottjer said, 鈥減articularly in the analysis of the possibility that the end-Triassic mass extinction was an ocean acidification event."
The geological record during the Triassic-Jurassic event provides scientists a strong indication that an ocean acidification event occurred. When the supercontinent Pangaea began to split apart into the continents that we know today, there was strong volcanic activity (volcanoes from Newfoundland to Morocco); these volcanoes caused atmospheric carbon dioxide levels to increase and the ocean鈥檚 pH level decreased.
Carbonic acids in the ocean can dissolve the shells of oysters and clams and also wreak havoc on marine life such as coral reefs. Lower pH levels also adversely affect nitrogen levels, which marine life rely on to survive, Martindale said.
Greene said the geological record parallels some important aspects of anthropogenic climate change 鈥� or the production of greenhouse gases emitted by human activity.
鈥淲e can look at the outcomes of these paleo-events to inform our predictions for the future,鈥� Greene said. 鈥淭he rate at which carbon dioxide is released to the atmosphere is critical in determining the severity of ocean chemistry change that will result 鈥� and the faster the carbon dioxide release the worse it gets.鈥�
Although similarities exist, no past event perfectly parallels future projections in terms of disrupting the balance of ocean carbonate chemistry, Martindale noted.
鈥淲e want scientists and governments to look at these past events and learn from them,鈥� Martindale said. 鈥淲e see intervals in the rock record when pH dropped and those events led to extinctions of marine organisms. That result is really powerful because we鈥檙e showing it happened before and could happen again.鈥�
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