ALBUQUERQUE, N.M. — A scientist at the University of New Mexico, along with her colleagues, has uncovered evidence that supports the belief that decreasing oxygen levels in the ocean contributed to the Earth’s first mass extinction.
The event is called anoxia and continues to occur in today’s oceans. Scientists have discovered pockets of ocean, called dead zones, that contain little to no oxygen. The phenomena near coastlines can be linked to human activities but the dead zones in the open ocean are mostly natural occurrences.
Maya Elrick, UNM professor of earth and planetary sciences, said studying what happened during the extinction 450 million years ago could help scientists understand, and in turn, address what is happening today.
“What are the extremes?” she said. “Were conditions (in the oceans) as bad as today, worse or better?”
Elrick, along with her former master’s student Rick Bartlett, who is now getting a Ph.D. at Louisiana State University; James Wheeley from the University of Birmingham in England; and Andre Desrochers from the University of Ottawa in Canada, are hoping to answer these questions by studying deposits left in marine limestone. Their research is in part funded by a three-year, $680,000 National Science Foundation grant.
“We study the concentration of uranium,” she said. “We look at the ratio of uranium isotopes. We look at not just how much uranium there is, but the types of uranium. It develops differently depending on the oxygen in the ocean.”
Elrick said the Earth has had five mass extinctions, which means at least 75 percent of species became extinct. During the first mass extinction, called the Ordovician-Silurian, there were only marine organisms and none on land yet, Elrick said. More than 80 percent of species became extinct during this time.
Elrick and her fellow researchers have traveled to several places, including Nevada, Germany, Austria, Italy and Anticosti Island in the St. Lawrence seaway of Quebec, Canada, to collect limestone rock samples, which are then brought back to UNM and analyzed. What she and her team have discovered is that oxygen levels in the oceans were low during the extinctions and for some time afterward but not before the event. The catalyst for the anoxia, she said, was a major ice age, which changed the oceans.
“We think the oceans started circulating more vigorously,” she said. “It brings things to the surface. That fertilized the phytoplankton.”
When the phytoplankton, which is a plant, dies, it needs oxygen to decompose. Essentially the decomposing plant sucks up all the oxygen, making it impossible for anything else to live there. The team will continue testing samples from different locations to determine whether the anoxia was global.
“We don’t know what ancient oxygen levels were like,” she said. “We don’t know what the whole ocean was like.”
In current day, coastal dead zones are linked to pollution, some from farming, that runs into the ocean and fertilizes the phytoplankton, helping it thrive. In the open ocean, it’s believed global warming is partly to blame for the growing dead zones because warm water carries less oxygen.
Although part of the overall picture, anoxic events aren’t the only culprit of the mass extinctions. Scientists have also blamed massive volcanic eruptions, meteors, asteroid collisions, acidic oceans and falling sea levels. It’s an area that scientists continue to study and understand.
Elrick and her team hope to add to that understanding.