Where did Earth’s oxygen come from? The answer may surprise

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 distant past – already in the new era, from 2.8 to 2.5 billion years ago – This oxygen was almost absent🇧🇷

So how did Earth’s atmosphere become oxygenated?

Our researchpublished in Natural Earth Sciencesadds a tantalizing new possibility: that at least some of Earth’s early oxygen came from a tectonic source through crustal movement and destruction.

Archean land

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

This strange land was a covered water world green oceanswrapped in methane haze And without a completely multicellular life. Another strange aspect of this world is the nature of its tectonic activity.

On modern Earth, the dominant tectonic activity is called plate tectonics, as the oceanic crust—the outermost layer of the Earth beneath the oceans—sinks into the mantle (the area between the Earth’s crust and core) at meeting points called zones. subduction. However, there is considerable debate as to whether plate tectonics worked in the Archean era.

A feature of recent subduction zones is their association with oxidized magma🇧🇷 This magma forms when oxidized sediments and deep waters – cold, dense waters form near the ocean floor inserted into the Earth’s mantle🇧🇷 It produces magma with a high content of oxygen and water.

Our research aims to test whether the absence of oxidants in waters and deep bottom sediments can prevent the formation of oxidised magmas. The identification of such magma in new igneous rocks could provide evidence that subduction and plate tectonics occurred 2.7 billion years ago.

Experience

We collected samples of granite rocks dating from 2,750 to 2,670 billion years ago throughout the Abitibi Wawa sub-province of the Upper Province (Canada) – the largest preserved Archean continent, which stretches for more than 2,000 km from Winnipeg, in the province of Manitoba, to the easternmost province Quebec. This allowed us to investigate the level of oxidation of magma generated during the new age.

Measuring the oxidation state of these igneous rocks — formed through the cooling and crystallization of magma or lava — is challenging. Post-crystallization events may have modified these rocks through further deformation, burial, or heating.

So we decided to look at the mineral apatite found in the zirconium crystals of these rocks. Zirconium crystals can withstand extreme temperatures and pressures for post-crystallization events. They hold clues about the environments in which they were originally formed and provide accurate ages for the rocks themselves.

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

We were able to successfully measure the oxygen intensity of the original Archean magma—which is 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 Synchrotron Photon Source at Argonne National Laboratory in Illinois (USA). United States of America).

producing oxygen from water?

We found that the sulfur content in the magma, which was initially about zero, increased to 2,000 ppm about 2.705 billion years ago. This indicates that the magma has become richer in sulfur. In addition to Predominance of S6 + – a type of sulfur ion – in apatite He suggested that the sulfur was from an oxidizing source, combined with Host zirconium crystal data🇧🇷

These new discoveries indicate that the oxidized magma formed in the modern era, 2.7 billion years ago. The data indicate that the lack of dissolved oxygen in ancient oceanic reservoirs did not prevent the formation of sulfur-rich, oxidized magmas at subduction zones. The oxygen in this magma must have come from another source and was finally released into the atmosphere during volcanic eruptions.

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

The mechanism is not yet clear

The implications of this oxidized magma go beyond understanding the geodynamics of the early Earth. Previously, it was thought that Archean magma was less likely to oxidize when it is ocean water And the rocks or sediments From the bottom of the ocean they were not.

While the exact mechanism is not clear, the occurrence of this magma suggests that the process of subduction, in which ocean water is pushed hundreds of kilometers into our planet, generates free oxygen. This then oxidizes the upper mantle.

Our study shows that ancient subduction may have been a vital and unexpected factor in Earth’s oxygenation, Oxygen puffed out 2.7 billion years ago as well The Great Oxidation Event, which saw atmospheric oxygen increase by 2% from 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 – with active plate tectonics and subduction. This suggests that this study could partially explain the lack of oxygen and eventually life on other rocky planets in the future as well.

* David Moll is a Postdoctoral Professor of Geosciences at Laurentian University (Canada); Adam Charles Simon Professor of Earth and Environmental Sciences at the University of Michigan (USA); Xuyang Meng is a postdoctoral professor of earth and environmental sciences at the University of Michigan.

🇧🇷 And theThis article Reposted from the site Conversation Under Creative Commons Licence🇧🇷 Read the original article over here🇧🇷

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