Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Oxygen's ups and downs in the early atmosphere and ocean

24.10.2012
UC Riverside-led research team finds evidence for a dramatic rise in early oxygen about 2.3 billion years ago followed, more surprisingly, by an equally impressive fall

Most researchers imagine the initial oxygenation of the ocean and atmosphere to have been something like a staircase, but with steps only going up.


This is a carbonate rock in Zimbabwe used to trace sulfate levels in the Earth's early oceans.

Credit: Lyons Lab, UC Riverside

The first step, so the story goes, occurred around 2.4 billion years ago, and this, the so-called Great Oxidation Event, has obvious implications for the origins and evolution of the first forms of eukaryotic life. The second big step in this assumed irreversible rise occurred almost two billion years later, coinciding with the first appearances and earliest diversification of animals.

Now a team led by geochemists at the University of California, Riverside challenges the simple notion of an up-only trend for early oxygen and provides the first compelling direct evidence for a major drop in oxygen after the first rise.

"Our group is among a subset of scientists who imagine that oxygen, once it began to accumulate in the ocean-atmosphere system, may have ultimately risen to very high levels about 2.3-2.2 billion years ago, perhaps even to concentrations close to what we see today," said Timothy Lyons, a professor of biogeochemistry and the principal investigator of the project. "But unlike the posited irreversible rise favored by many, our new data point convincingly to an equally impressive, and still not well understood, fall in oxygen about 200 million years later."

According to Lyons, this drop in oxygen may have ushered in more than a billion years that were marked by a return to low-oxygen concentrations at Earth's surface, including the likelihood of an oxygen-free deep ocean.

"It is this condition that may have set the environmental stage and ultimately the clock for the advance of eukaryotic organisms and eventually animals," he said.

Study results appear online this week in the Proceedings of the National Academy of Sciences.

"The time window between 2.3 and 2.1 billion years ago is famous for the largest and longest-lived positive carbon isotope excursion in Earth history," said Noah Planavsky, a recent Ph.D. graduate from UC Riverside, current postdoctoral fellow at Caltech, and first author of the research paper.

He explained that carbon isotopes are fractionated during photosynthesis. When organic matter is buried, oxygen is released and rises in the biosphere. The burial of organic matter is tracked by the positive or heavy isotopic composition of carbon in the ocean.

"Some workers have attributed the carbon isotope excursion to something other than organic burial and associated release of oxygen," Planavsky said. "We studied the sulfur isotope composition of the same rocks used for the carbon isotope analyses — from Canada, South Africa, the U.S., and Zimbabwe — and demonstrated convincingly that the organic burial model is the best answer."

The researchers' sulfur data point to high sulfate concentrations in the ocean, which, like today, is a classic fingerprint of high oxygen levels in the ocean and atmosphere. Sulfate, the second most abundant negatively charged ion in the ocean today, remains high when the mineral pyrite oxidizes easily on the continents and is buried in relatively small amounts in the oxygen-rich ocean.

"What is equally impressive is that the rise in oxygen was followed by a dramatic fall in sulfate and therefore oxygen," Lyons said. "Why the rise and fall occurred and how that impacted the billion years or more of ocean chemistry that followed and the life within that ocean are hot topics of research."

The research team is thrilled to have found strong chemical evidence for oxygen variability on the early Earth.

"The idea that oxygen levels at Earth's surface went up and down must be vital in any effort to understand the links between environmental and biological evolution on broad, geologic time scales," Planavsky said.

He and Lyons were joined in the study by Andrey Bekker at the University of Manitoba, Axel Hofmann at the University of Johannesburg and Jeremy Owens at UCR.

The NASA Exobiology Program supported this research. A National Science Foundation (NSF) Graduate Research Fellowship and a postdoctoral fellowship from the NSF Division of Earth Sciences covered Planavsky's salary.

The University of California, Riverside (www.ucr.edu) is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment has exceeded 20,500 students. The campus will open a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of more than $1 billion. A broadcast studio with fiber cable to the AT&T Hollywood hub is available for live or taped interviews. UCR also has ISDN for radio interviews. To learn more, call (951) UCR-NEWS.

Iqbal Pittalwala | EurekAlert!
Further information:
http://www.ucr.edu

More articles from Earth Sciences:

nachricht New research calculates capacity of North American forests to sequester carbon
16.07.2018 | University of California - Santa Cruz

nachricht Scientists discover Earth's youngest banded iron formation in western China
12.07.2018 | University of Alberta

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Machine-learning predicted a superhard and high-energy-density tungsten nitride

18.07.2018 | Materials Sciences

NYSCF researchers develop novel bioengineering technique for personalized bone grafts

18.07.2018 | Life Sciences

Why might reading make myopic?

18.07.2018 | Health and Medicine

VideoLinks
Science & Research
Overview of more VideoLinks >>>