The appearance of oxygen in the Earth's atmosphere probably did not occur as a single event, but as a long series of starts and stops, according to geoscientists who investigated rock cores from the FAR DEEP project. The Fennoscandia Arctic Russia - Drilling Early Earth Project--FAR DEEP--took place during the summer of 2007 near Murmansk in Northwest Russia.
Panorama of Russia's Imandra/Varzuga Greenstone Belt where FAR DEEP drilling took place. Credit: Victor Melezhik, Geological Survey of Norway/University of Bergen
The project, part of the International Continental Scientific Drilling Program, drilled a series of shallow, two-inch diameter cores and, by overlapping them, created a record of stone deposited during the Proterozoic Eon--2,500 million to 542 million years ago.
"We've always thought that oxygen came into the atmosphere really quickly during an event," said Lee Kump, a geoscientist at Penn State University.
"We are no longer looking for an event. Now we're looking for when and why oxygen became a stable part of the Earth's atmosphere."
The researchers report in this week's issue of the journal Science Express that evaluation of these cores, in comparison with cores from Gabon previously analyzed by others, supports the conclusion that the Great Oxidation Event, the appearance of free oxygen in Earth's atmosphere, played out over hundreds of millions of years. Kump is the lead author of the Science Express paper.
Oxygen levels gradually crossed the low atmospheric oxygen threshold for pyrite--an iron sulfur mineral--oxidation by 2,500 million years ago, and the loss of what scientists call mass-independently fractionated (MIF) sulfur by 2,400 million years ago.
Then oxygen levels rose at an ever-increasing rate through the Paleoproterozoic, achieving about one percent of the present atmospheric level.
"The definition of when an oxygen atmosphere occurred depends on which threshold you are looking for," said Kump. "It could be when pyrite becomes oxidized, when sulfur MIF disappears, or when deep crustal oxidation occurs."
When the MIF sulfur disappeared, the air on Earth was still not breathable by animal standards.
When red rocks containing iron oxides appeared 2,300 million years ago, the air was still unbreathable.
"At about one percent oxygen, the groundwater became strongly oxidized, making it possible for water seeping through rocks to oxidize organic materials," said Kump.
Initially, any oxygen in the atmosphere, produced by the photosynthesis of single-celled organisms, was used up when sulfur, iron and other elements oxidized.
When sufficient oxygen accumulated in the atmosphere, it permeated the groundwater and began oxidizing buried organic material, oxidizing carbon to create carbon dioxide.
"Insights into Earth's carbon cycle offer tantalizing clues to the history of atmospheric oxygen levels, and Kump and others have revealed unrecognized details of the timing and mechanism of the Great Oxidation Event," said Enriqueta Barrera, program director in the National Science Foundation's Division of Earth Sciences, which funded the research.
The cores from the FAR-DEEP project were compared with samples from Gabon using the ratio of carbon isotopes, or variants, 13 and 12 to see if the evidence for high rates of oxygen accumulation existed worldwide.
Both the FAR-DEEP project's cores and the Gabon cores show large deposits of carbon in the form of fossilized petroleum.
Both sets of cores also show similar changes in carbon 13 through time, indicating that the changes in carbon isotopes occurred worldwide and that oxygen levels throughout the atmosphere were high.
"Although others have documented huge carbon isotope variations at later times in Earth history associated with stepwise increases in atmospheric oxygen, our results are less equivocal because we have many lines of data all pointing to the same thing," said Kump.
"These indications include not only carbon 13 isotope profiles in organic mater from two widely separated locations, but also supporting profiles in limestones and no indication that processes occurring since that time have altered the signal."
Working with Kump on the project were geoscientists Michael Arthur of Penn State; Christopher Junium of Syracuse University; Alex Brasier and Anthony Fallick of the Scottish Universities Environmental Research Centre; Victor Melezhik, Aivo Lepland and Alenka Crne at the Norwegian Geological Survey; and Genming Luo, China University of Geosciences.
The NASA Astrobiology Institute also supported the research.Media Contacts
Cheryl Dybas | EurekAlert!
AWI researchers measure a record concentration of microplastic in arctic sea ice
24.04.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
Climate change in a warmer-than-modern world: New findings of Kiel Researchers
24.04.2018 | Christian-Albrechts-Universität zu Kiel
At the Hannover Messe 2018, the Bundesanstalt für Materialforschung und-prüfung (BAM) will show how, in the future, astronauts could produce their own tools or spare parts in zero gravity using 3D printing. This will reduce, weight and transport costs for space missions. Visitors can experience the innovative additive manufacturing process live at the fair.
Powder-based additive manufacturing in zero gravity is the name of the project in which a component is produced by applying metallic powder layers and then...
Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.
Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
25.04.2018 | Physics and Astronomy
25.04.2018 | Physics and Astronomy
25.04.2018 | Information Technology