UW scientist: Sea level changes a driving force in mass extinctions


Watch out for the oceans.

That’s the lesson of an extensive study by University of Wisconsin-Madison assistant professor Shanan Peters published June 15 in the journal Nature.

Peters looked at data gathered by scientists over many years and analyzed what they found at about 600 locations all over the continental United States and Alaska, going back more than 500 million years.

Changes in ocean environments related to sea level exert a driving influence on rates of extinction, which animals and plants survive or vanish, and the composition of life in the ocean, he found.

“This breakthrough speaks loudly to the future impending modern (oceanic) shelf destruction due to climate change on earth,” said National Science Foundation program manager Rich Lane.

No matter what the cause of the ebb and flow of the oceans in various eras, the repeated and resultant extinctions must be considered, Lane said.

Scientists say there may have been as many as 23 mass extinction events over the last 3.5 billion years on earth, many involving simple forms of life such as single-celled microorganisms.

Over the past 540 million years, there have been five well-documented mass extinctions, primarily of maritime plants and animals, with as many as 75-95 percent of species lost.

For the most part, scientists have been unable to pin down the causes of the dramatic events, though in the case of the demise of the dinosaurs, they suspect that a large asteroid crashed into the planet.

“Impacts, for the most part, aren’t associated with most extinctions,” Peters said in an interview. “There have also been studies of volcanism, and some eruptions correspond to extinction, but many do not.”

So the assistant professor of geology and geophysics looked at sea levels by reviewing previous studies of the geological record, which show a clear difference in composition of the earth when it is covered by the sea and when it is not.

He measured two types of marine shelf environments, one where sediments were derived from land erosion and the other composed primarily of calcium carbonate, which is produced in place by shelled organisms and chemical processes.

In the course of hundreds of millions of years the world’s oceans have expanded and contracted in response to movement of the Earth’s crust and changes in climate. There were periods when vast areas of continents, including Wisconsin, were flooded by shallow seas.

“Most of the major extinctions have come when sea levels were high,” Peters explained.

“Anything we can learn about how the physical environment and life has changed in the past will tell us what to expect in the future.”

The sea level has changed dramatically in the past, with each ice age, for instance, and 14,000 years ago there was ice over Madison, he said.

So in respect to climate change, he said, sea level will change whether the climate is warming or cooling.

“The bottom line is that the biosphere is well primed for the type of sea level change we are likely to see as a result of global warming,” Peters said.

“The biggest thing we should worry about is the impact of sea level rise on humans. The scariest part is sea level rise from a human perspective in my opinion, because so many people live close to the sea. The toll will be large.”


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Filed under biodiversity, conservation, environment, extinction, nature, wildlife

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