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Where Did Earth’s Oxygen Come From? Scientists Hint At An Unexpected Source


Where does Earth's oxygen come from?  Scientists hint at an unexpected source

The amount of oxygen in Earth’s atmosphere makes it a habitable planet. (Represent)

Michigan:

The amount of oxygen in Earth’s atmosphere makes it a habitable planet.

Twenty-one percent of the atmosphere consists of this life-giving element. But in the deep past – as far back as the Neo-Archaic period 2.8 to 2.5 billion years ago – This oxygen is almost absent.

So, how did Earth’s atmosphere become oxygenated?

Our researchpublished year natural geosciencesadds an exciting new possibility: that at least some of Earth’s original oxygen came from a tectonic source through the movement and destruction of the Earth’s crust.

Archean Earth

The Archean period represents a third of our planet’s history, from 2.5 billion years ago to 4 billion years ago.

This alien earth is a water world, covered with blue oceancovered in a methane smoke and a complete lack of multicellular life. Another alien aspect of this world is its tectonic nature.

On modern Earth, the predominant tectonic activity is known as plate tectonics, in which oceanic crust — the Earth’s outermost layer under the oceans — sinks into the Earth’s mantle ( the area between the Earth’s crust and its core) at the points of convergence is called the subduction zone. However, there is considerable debate as to whether plate tectonics is active going back to the Archean era.

A feature of modern subduction zones is their association with oxidized magma. These magmas are formed when sediments are oxidized and bottom water – cold, dense water near the ocean floor – is introduced into the Earth’s mantle. This creates magma with high oxygen and water content.

Our study aimed to test whether the absence of oxidized materials in Archean bedrock water and sediments could prevent the formation of oxidized magma. The identification of such magmas in Neoarchean magma could provide evidence that plate tectonics and subduction occurred 2.7 billion years ago.

Experiment

We collected samples of granitoid rocks between 2750 and 2670 million years old from across the Abitibi-Wawa sub-province of the Superior Province – the largest preserved Archean continent stretching over 2000 km from Winnipeg, Manitoba to far eastern Quebec. This allowed us to investigate the degree of oxidation of magma generated during the Neoclassical period.

Dr. Xuyang Meng is collecting a rock sample in Rouyn-Noranda, Que.
2750 to 2670 million-year-old granitoids collected from the largest preserved Archean continent may help reveal the origin story of Earth’s oxygen.(Dylan McKevitt), provided by the author

Measuring the oxidation state of these magmatic rocks – formed through the cooling and crystallization of magma or lava – is challenging. Post-crystallization events may have transformed these rocks through later deformation, burial, or heating.

So we decided to consider mineral apatite present in zircon crystal in these rocks. Zircon crystals can withstand the extreme temperatures and pressures of post-crystallization events. They keep clues about the environment in which they were originally formed and provide precise ages for the rocks themselves.

Tiny apatite crystals less than 30 microns wide — the size of a human skin cell — are trapped within the zircon crystals. They contain sulfur. By measuring the amount of sulfur in apatite, we can determine if apatite has grown from oxidized magma.

A map of Canada showing the location of the Province of Superior in the east of the country.
Superior province map stretching from central Manitoba to eastern Quebec in Canada.(Xuyang Meng), provided by the author

We were able to measure success the escape of oxygen of the original Archean magma – essentially the amount of free oxygen in it – using a specialized technique called X-ray Absorption Near Edge Structure Spectroscopy (S-XANES) at the Advanced Photon Source synchrotron at Argonne National Laboratory in Illinois.

Generate oxygen from water?

We found that the magma sulfur content, initially near zero, increased to 2000 parts per million at about 2705 million years. This suggests that the magma has become richer in sulfur. In addition, the predominance of S6+ — a sulfur ion — in apatite suggests that sulfur is from an oxidizing source, consistent with data from host zircon crystals.

These new findings indicate that oxidized magma formed during the Neo-Archaic era 2.7 billion years ago. The data suggest that the lack of dissolved oxygen in Archean oceanic reservoirs does not prevent the formation of sulfur-rich, oxidizing magma in subduction zones. The oxygen in these magma must have come from another source, and is eventually released into the atmosphere during volcanic eruptions.

We found that the occurrence of these oxidized magmas correlated with major gold mineralization events in Superior Province and Yilgarn Craton (Western Australia), demonstrating a link between these oxygen-rich sources and formation world-class ore mines.

The significance of these oxidized magma goes beyond understanding the early geodynamics of the Earth. Previously, it was thought that Archean magma could not be oxidized, when Seawater and ocean floor rocks or sediments did not.

Although the exact mechanism is still unclear, the appearance of these magma suggests that the process of subduction, in which seawater is brought hundreds of kilometers into our planet, produces free oxygen. This then oxidizes the top coating.

Our study suggests that Archean subduction may have been an important, unforeseen factor in the early, early Earth oxidation. oxygen flow 2.7 billion years ago and also The Great Oxidation Event, which marked an increase in atmospheric oxygen by two percent 2.45 to 2.32 billion years ago.

As far as we know, Earth is the only place in the solar system – past or present – that has active plate tectonics and subduction. This suggests that this study could partly explain the hypoxia and, ultimately, life on other rocky planets in the future.Conversation

(author:david’s molePostdoctoral Fellow, Earth Science, Laurentian University; Adam Charles SimonArthur F. Thurnau Professor, Earth & Environmental Sciences, University of Michiganand Xuyang MengPostdoctoral Fellow, Earth and Environmental Sciences, University of Michigan)

This post was reposted from Conversation under Creative Commons license. Read original article.

(Public statement: David Mole has received funding from the Canada First Research Excellence Fund (CFREF) and additional federal, provincial and industry partners as part of the Metal Earth project; a Canadian geoscience research program led by Laurentian University. The $104 million project started in 2016 and is changing our understanding of the origins of base and precious metal deposits in Earth’s evolution. This initiative has created a strategic consortium of Canadian and international researchers, government and industry. The Metal Earth # funding project is CFREF-2015-00005. David is currently employed by Geoscience Australia, who was not involved in this work.

Adam C. Simon received grants from the US National Science Foundation EAR grants #2214119 and 1924142.

Xuyang Meng received funding from the Canada First Research Excellence Fund (CFREF-2015-00005), the Natural Science Foundation of China, the US National Science Foundation EAR, and a PhD fellowship from the Academic Council. China Scholarship)

(This story has not been edited by NDTV staff and was automatically generated from the aggregate feed.)

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