A geological researcher at the University of New Mexico has discovered that low oxygen levels contributed to the Earth’s great mass extinctions.
Maya Elrick, the sedimentary geologist behind the research, said ocean water anoxia — the depletion of dissolved oxygen in water — can be linked to four out of the five mass extinctions on Earth.
The earth has had five mass extinctions, and the Late Ordovician Mass Extinction occurred about 450 million years ago. This extinction was when most life on earth was in the sea and resulted in a drastic reduction of species.
Elrick and her colleagues made this discovery while working in a remote part of Canada. The scientists sampled limestone to reveal levels of oxygen in the ocean at the time of the extinction. According to Elrick, the tool used to make this discovery is still fairly new — making this research groundbreaking.
The tool measures the levels of uranium isotopes in limestone sediments, as limestone precipitates from the seawater, meaning it will contain whatever elements were present in the seawater at the time.
When examining limestone, Elrick dissolves the samples, releasing the elements trapped during that time period, which allows the researchers to measure the levels of uranium isotopes. It is the ratio of uranium isotopes that revealed to Elrick the presence of anoxic seawater at the time of the extinction.
“This tells me how much of the sea floor was underlane by anoxic waters. If there is anoxic water, uranium gets sequestered into the anoxic sediments,” Elrick said. “More uranium gets pulled out of the water leaving the sea water less enriched in uranium.”
The limestone samples reflect this phenomenon, allowing researchers to make observations about the global state of the seawater during the extinction. Previous tools that measured uranium isotopes only provided location specific information. Elrick said If there is anoxic seafloor then there had to have been anoxic seawater overlaying it.
Elrick has decided to examine all five mass extinctions with this tool in order to identify patterns surrounding the extinction. The first two extinctions have already been examined, and the paper she wrote about the third extinction is in review.
According to Yemane Asmerom, a geochemist in the UNM Department of Earth and Planetary Sciences, there have been multiple mass extinctions during Earth’s history. However, there is still much to be learned about these extinctions.
“Results from this project clearly show dramatic changes in the oxygen levels of the ocean during one the largest extinction events in earth history,” Asmerom said.
Elrick plans on collecting data that spans over 150 million years. She said this kind of long term data will provide more information and clues to what caused the extinctions. It will also provide information about current global patterns.
The sixth major extinction is happening right now, Elrick said, and like past extinctions there are low levels of oxygen in the water. However, she said humans are involved in the sixth major extinction, because the anoxia is caused by global warming.
Elrick said she hopes students learn that when facing a problem it is important to use all the resources available.
“I want (students) to understand the multiple tools used to attack one problem.”
Megan Holmen is the assistant news editor at the Daily Lobo. She can be contacted at firstname.lastname@example.org, email@example.com or on Twitter @megan_holmen.