Fossilized Plankton Provide Insight into Earth's Ancient Atmosphere
February 23, 2011 4:40 PM
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Study shows plankton became more diverse during a time when oxygen levels spiked in Earth's earliest breathable atmosphere
Ohio State University
have found that plankton play a large part in understanding the origin of Earth's first breathable atmosphere.
Matthew Saltzman, study leader and associate professor of earth sciences at Ohio State University, and a team of researchers, have discovered that
plankton are the key
to understanding the gap between the atmosphere and 500 million-year-old chemical isotopes found in rocks.
The Ohio State University team previously conducted a study that showed that upward displacements in the Earth's crust 500 million years ago lead to a reverse greenhouse effect, which cooled the oceans producing large plankton blooms, and sent oxygen into the atmosphere.
Now, Saltzman and his team have discovered how oxygen disappeared from Earth's atmosphere during the Cambrian Period and then reappeared at higher levels. The team was able to quantify exactly how much oxygen was released during this period, and linked the amount of sulfur in oceans at that time with atmospheric carbon dioxide and oxygen. They also looked at how oxygen allowed a large amount of new life to thrive after it returned.
"We know that oxygen levels in the ocean dropped dramatically [a condition called anoxia] during the Cambrian, and that coincides with
the time of a global extinction
," said Saltzman. "We still don't know why the anoxia spread all over the world. We may never know. But there have been many other extinction events in Earth's history, and with the exception of those caused by meteor impacts, others likely share elements of this one - changes in the balance of oxygen and carbon dioxide in the atmosphere and oceans."
When searching for what may have allowed oxygen back into the atmosphere and oceans 500 million years ago, researchers found that plankton played a huge role. During that time period, life didn't exist on land and life in the oceans was not as diverse as it is today, which made plankton a very big deal as far as ancient lifeforms go.
Then a geologic event called the Steptoean Positive Carbon Isotope Excursion (SPICE) occurred, burying large amounts of organic matter in ocean sediments. This pulled carbon dioxide from the atmosphere and in turn, released oxygen. As plankton encounter oxygen, they become more selective for the "light isotope of carbon in carbon dioxide" and absorb it.
Saltzman and his team looked at isotopes in fossilized plankton found in rocks located in the central United States,
and the Australian outback. They discovered that "plankton revolution," which is when plankton became more diverse, occurred around the same time as the SPICE event.
"The amount of oxygen rebounded, and so did the diversity of life," said Saltzman. "We were able to bring together independent lines of evidence that showed that if the total oxygen was around 5-10 percent before the SPICE, then it rose to just above modern levels for the first time after the SPICE."
Information that the plankton have provided could be used to possibly deter
by changing the chemistry of the ocean to remove carbon dioxide.
"When it comes to ancient life, they don't sound as exciting as dinosaurs, but the plankton are critical to this story," said Saltzman.
was published in
Proceedings of the National Academy of Sciences
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RE: What does this mean for Carbon dating accuracy
2/23/2011 7:35:03 PM
C14 really isn't something that comes into play in a discussion of the Cambrian. After about ten half-lives there isn't enough C14 left to measure, which limits its use to things dating less than about 57,000 years old. The Cambrian period is 500,000,000 years old. In addition, C14 is generated by the bombardment of nitrogen in the atmosphere by cosmic rays. You will find a few references to some very old things like diamond and petroleum yielding C14 dates, but the C14 source in that case isn't due to atmospheric C14 but due to exposure to a radiogenic source like uranium. In those cases, the little bit of C14 is just above background radiation, so the erroneous dates always come in at around ~50,000 yrs old.
None of rock dating techniques (e.g. Uranium-Lead, Potassium-Argon, etc.) rely on a variable mechanism like C14 generation or variable selectivity by an organism. Scientists rely on the chemical knowledge of crystals like zircon that always exclude lead but can include uranium when they crystallize. Therefore any lead they do find in a zircon crystal is due to radiometric decay of uranium. So... the answer is essentially "no". This does not occur for other elemental isotope ratios.
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