From Rice: “Oxygen atmosphere recipe = tectonics + continents + life”

Rice University

Rice-led study offers new answer to why Earth’s atmosphere became oxygenated

May 16, 2016
Jade Boyd

Earth scientists from Rice University, Yale University and the University of Tokyo are offering a new answer to the long-standing question of how our planet acquired its oxygenated atmosphere.

Based on a new model that draws from research in diverse fields including petrology, geodynamics, volcanology and geochemistry, the team’s findings* were published online this week in Nature Geoscience. They suggest that the rise of oxygen in Earth’s atmosphere was an inevitable consequence of the formation of continents in the presence of life and plate tectonics.

“It’s really a very simple idea, but fully understanding it requires a good bit of background about how the Earth works,” said study lead author Cin-Ty Lee, professor of Earth science at Rice. “The analogy I most often use is the leaky bathtub. The level of water in a bathtub is controlled by the rate of water flowing in through the faucet and the efficiency by which water leaks out through the drain. Plants and certain types of bacteria produce oxygen as a byproduct of photosynthesis. This oxygen production is balanced by the sink: reaction of oxygen with iron and sulfur in the Earth’s crust and by back-reaction with organic carbon. For example, we breathe in oxygen and exhale carbon dioxide, essentially removing oxygen from the atmosphere. In short, the story of oxygen in our atmosphere comes down to understanding the sources and sinks, but the 3-billion-year narrative of how this actually unfolded is more complex.”

Lee co-authored the study with Laurence Yeung and Adrian Lenardic, both of Rice, and with Yale’s Ryan McKenzie and the University of Tokyo’s Yusuke Yokoyama. The authors’ explanations are based on a new model that suggests how atmospheric oxygen was added to Earth’s atmosphere at two key times: one about 2 billion years ago and another about 600 million years ago.

Today, some 20 percent of Earth’s atmosphere is free molecular oxygen, or O2. Free oxygen is not bound to another element, as are the oxygen atoms in other atmospheric gases like carbon dioxide and sulfur dioxide. For much of Earth’s 4.5-billion-year history, free oxygen was all but nonexistent in the atmosphere.

“It was not missing because it is rare,” Lee said. “Oxygen is actually one of the most abundant elements on rocky planets like Mars, Venus and Earth. However, it is one of the most chemically reactive elements. It forms strong chemical bonds with many other elements, and as a result, it tends to remain locked away in oxides that are forever entombed in the bowels of the planet — in the form of rocks. In this sense, Earth is no exception to the other planets; almost all of Earth’s oxygen still remains locked away in its deep rocky interior.”

Lee and colleagues showed that around 2.5 billion years ago, the composition of Earth’s continental crust changed fundamentally. Lee said the period, which coincided with the first rise in atmospheric oxygen, was also marked by the appearance of abundant mineral grains known as zircons.

“The presence of zircons is telling,” he said. “Zircons crystallize out of molten rocks with special compositions, and their appearance signifies a profound change from silica-poor to silica-rich volcanism. The relevance to atmospheric composition is that silica-rich rocks have far less iron and sulfur than silica-poor rocks, and iron and sulfur react with oxygen and form a sink for oxygen.

A view of Earth’s atmosphere taken from the International Space Station in 2003. (Photo courtesy of ISS Expedition 7 Crew, EOL, NASA)

“Based on this, we believe the first rise in oxygen may have been due to a substantial reduction in the efficiency of the oxygen sink,” Lee said. “In the bathtub analogy, this is equivalent to partially plugging the drain.”

Lee said the study suggests that the second rise in atmospheric oxygen was related to a change in production — analogous to turning up the flow from the faucet.

“The bathtub analogy is simple and elegant, but there’s an added complication that must be taken into account,” he said. “That is because oxygen production is ultimately tied to the global carbon cycle — the cycling of carbon between the Earth, the biosphere, the atmosphere and oceans.”

Lee said the model showed that Earth’s carbon cycle has never been at a steady state because carbon slowly leaks out as carbon dioxide from Earth’s deep interior to the surface through volcanic activity. Carbon dioxide is one of the key ingredients for photosynthesis.

“On long, geologic timescales, carbon is removed from the atmosphere by the production of condensed forms of carbon, such as organic carbon and minerals called carbonate,” he said. “For most of Earth’s history, most of this carbon has been deposited not in the deep ocean but rather on the margins of continents. The implications are profound because carbon deposited on continents does not return to Earth’s deep interior. Instead, it amplifies carbon inputs into the atmosphere when the continents are subsequently perturbed by volcanism.”

Lee said the team’s model showed that volcanic activity and other geologic inputs of carbon into the atmosphere may have increased with time, and because oxygen production is tied to carbon production, oxygen production also must increase. The model showed that the second rise in atmospheric oxygen had to occur late in Earth’s history.

“Exactly when is model-dependent, but what is clear is that the formation of continental crust naturally leads to two rises in atmospheric oxygen, just as we see in the fossil record,” Lee said.

Exactly what caused the composition of the crust to change during the first oxygenation event remains a mystery, but Lee said the team believes it may have been related to the onset of plate tectonics, where the Earth’s surface, for the first time, became mobile enough to sink back down into Earth’s deep interior.

The tectonic plates of the world were mapped in 1996, USGS.

Lee said the team’s new model is not without controversy. For example, the model predicts that production of carbon dioxide must increase with time, a finding that goes against the conventional wisdom that carbon fluxes and atmospheric carbon dioxide levels have steadily decreased over the last 4 billion years.

“The change in flux described by our model happens over extremely long time periods, and it would be a mistake to think that these processes that are bringing about any of the atmospheric changes are occurring due to anthropomorphic climate change,” he said. “However, our work does suggest that Earth scientists and astrobiologists may need to revisit what we think we know about Earth’s early history.”

This work is the result of an ongoing study of the global carbon cycle funded by the National Science Foundation and administered by Rice University.

[Note mentioned in this article, the activity of cyanobacteria which were the creatures which released the oxygen we breathe.]

*Science paper:
Two-step rise of atmospheric oxygen linked to the growth of continents

See the full article here .

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In his 1912 inaugural address, Rice University president Edgar Odell Lovett set forth an ambitious vision for a great research university in Houston, Texas; one dedicated to excellence across the range of human endeavor. With this bold beginning in mind, and with Rice’s centennial approaching, it is time to ask again what we aspire to in a dynamic and shrinking world in which education and the production of knowledge will play an even greater role. What shall our vision be for Rice as we prepare for its second century, and how ought we to advance over the next decade?

This was the fundamental question posed in the Call to Conversation, a document released to the Rice community in summer 2005. The Call to Conversation asked us to reexamine many aspects of our enterprise, from our fundamental mission and aspirations to the manner in which we define and achieve excellence. It identified the pressures of a constantly changing and increasingly competitive landscape; it asked us to assess honestly Rice’s comparative strengths and weaknesses; and it called on us to define strategic priorities for the future, an effort that will be a focus of the next phase of this process.

From LLNL: “Research lends new view of the Earth’s core”

Lawrence Livermore National Laboratory

Sep. 22, 2015

Anne M Stark
stark8@llnl.gov
925-422-9799

This model shows planetesimals (objects formed from dust, rock and other materials that can be anywhere in size from several meters to hundreds of kilometers) accreting to a growing Earth 4.56 billion years ago. The cutaway reveals the simultaneous formation of the Earth’s core as dense, iron-rich metallic material descending through a planetary magma ocean. Image courtesy of Antoine Pitrou/Institut de Physique du Globe de Parise Physique

There is more oxygen in the core of Earth than originally thought.

Lawrence Livermore geologist Rick Ryerson and international colleagues discovered some new findings about Earth’s core and mantle by considering their geophysical and geochemical signatures together.

This research provides insight into the origins of Earth’s formation.

Based on the higher oxygen concentration of the core, Ryerson’s team concludes that Earth must have accreted material that is more oxidized than the present-day mantle, similar to that of planetesimals such as asteroidal bodies. A planetesimal is an object formed from dust, rock and other materials and can be can be anywhere in size from several meters to hundreds of kilometers.

Earth formed about 4.56 billion years ago over a period of several tens of millions of years through the accretion of planetary embryos and planetesimals. The energy delivered by progressively larger impacts maintained Earth’s outer layer and an extensively molten magma ocean. Gravitational separation of metal and silicate within the magma ocean results in the planet characterized by a metallic core and a silicate mantle.

The formation of Earth’s core left behind geophysical and geochemical signatures in the core and mantle that remain to this day. In the past, core formation models have only attempted to address the evolution of core and mantle compositional signatures separately rather than looking for a joint solution.

By combining experimental petrology, geochemistry, mineral physics and seismology, the team found that core formation occurred in a hot (liquid) moderately deep magma ocean not exceeding 1,800-kilometer depth, under conditions more oxidized than present-day Earth.

“This new model is at odds with the current belief that core formation occurred under reduction conditions,” Ryerson said. “Instead we found that Earth’s magma ocean started out oxidized and has become reduced through time by oxygen incorporation into the core.”

They found the oxygen concentrations in the core are higher than previously thought and silicon concentrations are lower than previous estimates.

Other collaborators include Institut de Physique du Globe de Paris, École Polytechnique Fédérale de Lausanne and University College London.

The research appears in the online edition of the Sept. 21-25 edition of the Proceedings of the National Academy of Sciences (link is external).

See the full article here .

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From PNNL: “Oxygen: Not at All Random”

PNNL Lab

July 2015

Rejecting random diffusion, oxygen atoms create detailed architectures in uranium dioxide, radically altering our understanding of corrosion

Oxygen atoms follow a set pattern in corroding uranium dioxide, the primary component of fuel rods in nuclear reactors, not random diffusion. Understanding this pattern opens new doors for controlling corrosion. Image by Cortland Johnson, PNNL.

Results: Corrosion follows a different path when it comes to uranium dioxide, the primary component of the rods that power nuclear reactors, according to a new study by scientists at the Pacific Northwest National Laboratory, University of Chicago, and the Stanford Synchrotron Radiation Lightsource. In uranium dioxide, the oxygen atoms-key corrosion creators-do not diffuse randomly through the material. Rather, the oxygen atoms settle into the third, sixth, ninth, etc., layers. They space themselves within the layers and alter the structure by causing the layers of uranium atoms above and below to draw closer to the oxygen. The oxygen atoms essentially self-assemble into a highly structured array.

Why It Matters: Oxygen’s interactions can extensively corrode materials, whether it is a car in a field or a fuel canister in a nuclear reactor. Under certain conditions, oxygen corrodes fuel rods and causes them to swell by more than 30 percent, creating problems during both routine operations and emergency situations. Also, this swelling can be a problem for long-term storage of nuclear waste. The study shows atomic-level changes counter to those shown by the classical diffusion model that states most of the oxygen atoms are near the surface. The new study gives scientists accurate information to understand the start of corrosion, possibly leading to new ways to avoid corrosion-related failures.

See the full article here.

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Pacific Northwest National Laboratory (PNNL) is one of the United States Department of Energy National Laboratories, managed by the Department of Energy’s Office of Science. The main campus of the laboratory is in Richland, Washington.

PNNL scientists conduct basic and applied research and development to strengthen U.S. scientific foundations for fundamental research and innovation; prevent and counter acts of terrorism through applied research in information analysis, cyber security, and the nonproliferation of weapons of mass destruction; increase the U.S. energy capacity and reduce dependence on imported oil; and reduce the effects of human activity on the environment. PNNL has been operated by Battelle Memorial Institute since 1965.

From AAAS: “Why there is so little breathable oxygen in space”

AAAS

5 May 2015
Ken Croswell

In one of the most detailed astronomical images ever produced, NASA/ESA’s Hubble Space Telescope captured an unprecedented look at the Orion Nebula. … This extensive study took 105 Hubble orbits to complete. All imaging instruments aboard the telescope were used simultaneously to study Orion. The Advanced Camera mosaic covers approximately the apparent angular size of the full moon.
NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team

NASA/ESA Hubble

You breathe it every minute, but there’s hardly any molecular oxygen—otherwise known as O2—in space. In 1998, NASA even launched a satellite that was supposed to find lots of molecular oxygen but never did—except when scientists, worried that the instrument was faulty, aimed it at Earth. Now, a ground-based experiment has revealed why this life-giving molecule is so rare in the cosmos: because oxygen atoms cling tightly to stardust, preventing them from joining together to form oxygen molecules. The discovery should yield insight into the chemical conditions that prevail when stars and planets arise.

Oxygen is the third most common element in the universe, after hydrogen and helium, and in the 1970s astronomers predicted that molecular oxygen would be the third most common interstellar molecule, after molecular hydrogen (H2) and carbon monoxide (CO). It obviously isn’t. In fact, astronomers have detected interstellar molecular oxygen in only two places: the Orion Nebula and the Rho Ophiuchi cloud.

Rho Ophiuchi cloud
A rich collection of colourful astronomical objects is revealed in this picturesque image of the Rho Ophiuchi cloud complex from NASA’s Wide-field Infrared Explorer, or WISE. The Rho Ophiuchi cloud (pronounced ‘oh-fee-yoo-ki’ and named after a bright star in the region) is found rising above the plane of the Milky Way in the night sky, bordering the constellations Ophiuchus and Scorpius. It’s one of the nearest star-forming regions to Earth, allowing us to resolve much more detail than in more distant similar regions, like the Orion nebula.

NASA WISE

But even there the molecule is much rarer than theory predicts. For example, hydrogen molecules in the Orion Nebula outnumber oxygen molecules a million to one.

To explain the scarcity, astronomers recently proposed that oxygen atoms bind tightly to the dust particles that pepper space clouds. “Everybody knows that the binding energy of atomic oxygen is very important,” says Jiao He, an experimental astrophysicist at Syracuse University in New York. “But there was no experimental measurement of this parameter.”

Now, He and his colleagues have measured this number. The scientists heated two types of solids that make up interstellar dust grains—water ice and silicate—to see how readily oxygen atoms escape. As they recently reported in The Astrophysical Journal, the binding energy of oxygen is more than twice what scientists had calculated decades ago: 0.14 electron volts for water ice and 0.16 electron volts for silicate. That’s high enough to keep oxygen atoms stuck to stardust without the minimal heat of cold interstellar clouds dislodging them. The Orion Nebula may owe its small quantity of molecular oxygen to a shock wave that ripped atoms from the dust grains; Earth’s air abounds with oxygen because trees and other plants put it there.

“It’s a very valuable measurement,” says Gary Melnick, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who recently predicted a binding energy about that high. “It explains a lot.”

Oxygen atoms that float away from interstellar dust grains can join to make molecular oxygen. But when they stay stuck to the grains, hydrogen atoms combine with the oxygen to create water ice (H2O) instead. The water can then become part of asteroids, comets, and planets, setting the stage for the creation of life.

Paul Goldsmith, an astronomer at the Jet Propulsion Laboratory in Pasadena, California, spent more than a quarter-century seeking interstellar molecular oxygen before finally succeeding when Europe’s Herschel Space Observatory examined the Orion Nebula in 2010 and detected the elusive molecule.

ESA/Herschel

“I may have been misguided in spending so many years searching for it, but in a way, with this laboratory data and all the Herschel data, we can really say well, we do understand it now.”

See the full article here.

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From Astrobiology: “Geologists re-write Earth’s evolutionary history books”

Astrobiology Magazine

Sep 6, 2014

Oxygen-producing life forms appeared at least 60 million years earlier than previously thought

The study site landscape is shown with boulders of the ancient soil in the foreground. Credit: Quentin Crowley

Geologists from Trinity College Dublin have rewritten the evolutionary history books by finding that oxygen-producing life forms were present on Earth some 3 billion years ago – a full 60 million years earlier than previously thought. These life forms were responsible for adding oxygen (O2) to our atmosphere, which laid the foundations for more complex life to evolve and proliferate.

Working with Professors Joydip Mukhopadhyay and Gautam Ghosh and other colleagues from the Presidency University in Kolkata, India, the geologists found evidence for chemical weathering of rocks leading to soil formation that occurred in the presence of O2.

Using the naturally occurring uranium-lead isotope decay system, which is used for age determinations on geological time-scales, the authors deduced that these events took place at least 3.02 billion years ago. The ancient soil (or paleosol) came from the Singhbhum Craton of Odisha, and was named the ‘Keonjhar Paleosol’ after the nearest local town.

The pattern of chemical weathering preserved in the paleosol is compatible with elevated atmospheric O2 levels at that time. Such substantial levels of oxygen could only have been produced by organisms converting light energy and carbon dioxide to O2 and water. This process, known as photosynthesis, is used by millions of different plant and bacteria species today.

Hand sample of 3.02 billion year old soil.

It was the proliferation of such oxygen-producing species throughout Earth’s evolutionary trajectory that changed the composition of our atmosphere – adding much more O2 – which was as important for the development of ancient multi-cellular life as it is for us today.

Quentin Crowley, Ussher Assistant Professor in Isotope Analysis and the Environment in the School of Natural Sciences at Trinity, is senior author of the journal article that describes this research which has just been published online in the world’s top-ranked Geology journal, Geology.

He said: “This is a very exciting finding, which helps to fill a gap in our knowledge about the evolution of the early Earth. This paleosol from India is telling us that there was a short-lived pulse of atmospheric oxygenation and this occurred considerably earlier than previously envisaged.”

The early Earth was very different to what we see today. Our planet’s early atmosphere was rich in methane and carbon dioxide and had only very low levels of O2. The widely accepted model for evolution of the atmosphere states that O2 levels did not appreciably rise until about 2.4 billion years ago. This ‘Great Oxidation Event‘ event enriched the atmosphere and oceans with O2, and heralded one of the biggest shifts in evolutionary history.

Paleosol – lower part and pale coloured – locally quarried for the mineral pyrophyllite.

Micro-organisms were certainly present before 3.0 billion years ago but they were not likely capable of producing O2 by photosynthesis. Up until very recently however, it has been unclear if any oxygenation events occurred prior to the Great Oxidation Event and the argument for an evolutionary capability of photosynthesis has largely been based on the first signs of an oxygen build-up in the atmosphere and oceans.

“It is the rare examples from the rock record that provide glimpses of how rocks weathered,” added Professor Crowley. “The chemical changes which occur during this weathering tell us something about the composition of the atmosphere at that time. Very few of these ‘paleosols’ have been documented from a period of Earth’s history prior to 2.5 billion years ago. The one we worked on is at least 3.02 billion years old, and it shows chemical evidence that weathering took place in an atmosphere with elevated O2 levels.”

There was virtually no atmospheric O2 present 3.4 billion years ago, but recent work from South African paleosols suggested that by about 2.96 billion years ago O2 levels may have begun to increase. Professor Crowley’s finding therefore moves the goalposts back at least 60 million years, which, given humans have only been on the planet for around a tenth of that time, is not an insignificant drop in the evolutionary ocean.

Professor Crowley concluded: “Our research gives further credence to the notion of early and short-lived atmospheric oxygenation.

This particular example is the oldest known example of oxidative weathering from a terrestrial environment, occurring about 600 million years before the Great Oxidation Event that laid the foundations for the evolution of complex life.”

See the full article here.

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