Sea Level Fluctuations Played a Crucial Role in Planet's Mass Extinctions
According to a new study published online in the journal Nature, the ocean may have played a critical role in precipitating many of the world's mass extinctions over the last 500 million years. Specifically, variations in sea level and sediments may have exerted a strong influence on extinction rates and thus molded the past and present composition of marine life, says Shanan Peters, an assistant professor of geology and geophysics at the University of Wisconsin-Madison. Exploring the causes of previous mass extinctionsScientists believe there have been up to 23 mass extinction events since life began on Earth over 3.5 billion years ago, 5 of which may have occurred over the last 540 million years. During these events, it is believed 75 - 95% of species, mostly of marine animals and plants, perished.
Past research aimed at pinpointing a culprit for these extinction events has mostly turned up empty. Besides for the well-documented asteroid crash that eliminated the dinosaurs, scientists' efforts to find clues in the geologic record have yielded mixed, if any, results. Peters' study has now demonstrated a clear link between past fluctuations in sea level and sediments and these extinction events, overturning the commonly held view among geologists that sea level declines had no impact on mass extinctions.
What the rock record tells usIn his study, Peters examined two types of marine shelf environments preserved in the rock record, one in which sediments were derived from land erosion and the other consisting mostly of calcium carbonate, produced by chemical processes and shell organisms. The difference in spatio-temporal dynamics and physical characteristics, such as stability and nutrient availability, indicates changes in biodiversity on marine shelves and the general environment that were caused by the extinctions.
Peters is quick to acknowledge that his findings don't necessarily preclude the role of other factors in precipitating the mass extinctions. The significance of his work, he says, is that it "links them and smaller events in terms of a forcing mechanism, and it also tells us something about who survives and who doesn't across these boundaries. These results argue for a substantial fraction of change in extinction rates being controlled by just one environmental parameter."
More importantly, it could serve as a portent of the consequences of climate change-influenced sea level rises, argues Rich Lane of the NSF: "This breakthrough speaks loudly to the future impending modern shelf extinction due to climate change on Earth."
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