Earth’s atmosphere is rich in oxygen, making it a habitable world.
This element is found in twenty-one per cent of the atmosphere. But in the deep past – as far back as the Neoarchean era 2.8 to 2.5 billion years ago – This oxygen was almost non-existent.
So how did Earth’s atmosphere oxygenate?
Our researchPublished in Nature GeoscienceThis suggests a new and exciting possibility: at least some of Earth’s first oxygen may have come from a tectonic source, which is the movement and destruction Earth’s crust.
The Archean Earth
The Archean eon covers one-third the planet’s history from 2.5 billion to 4 billion years back.
This alien Earth was covered in water. Green oceansThe mystery surrounding the aforementioned saga is cloaked in mystery. methane hazeIt is completely devoid of multi-cellular life. The nature of its tectonic activity was another alien aspect of the world.
On modern Earth, the dominant tectonic activity is called plate tectonics, where oceanic crust – the outermost layer of the Earth under the oceans – sinks into the Earth’s mantle (the area between the Earth’s crust and its core) at points of convergence called subduction zones.
There is much debate about whether plate tectonics existed in the Archean period.
Modern subduction zones are distinguished by their association with oxidized magmas.
These magmas are formed when oxidized sediments and bottom waters – cold, dense water near the ocean floor – are Incorporated into the Earth’s mantle. This results in magmas that have high water and oxygen content.
Our research sought to find out if Archean bottom waters and sediments are free of oxidized materials that could hinder the formation of oxidized magnesium.
These magmas could be found in Neoarchean magmatic rock, which could indicate that subduction and plate-tectonics took place 2.7 billion years ago.
The experiment
We collected samples of 2750- to 2670-million-year-old granitoid rocks from across the Abitibi-Wawa subprovince of the Superior Province – the largest preserved Archean continent stretching over 2,000 kilometers (1,243 miles) from Winnipeg, Manitoba, to far-eastern Quebec.
This enabled us to examine the extent of oxidation in magmas that was generated during the Neoarchean period.
Measuring the oxidation-state of these magmatic rocks – formed through the cooling and crystalization of magma or lava – is challenging. These rocks may have been altered by post-crystallization events, such as burial or heating.
So we decided to examine the mineral apatiteThis is also present in the zircon crystalsThese rocks.
Zircon crystals can withstand extreme temperatures and pressures after post-crystallization. They provide accurate ages and clues about the environment in which they were formed.
Small apatite crystals that are less than 30 microns wide – the size of a human skin cell – are trapped in the zircon crystals. They also contain sulfur. We can determine if the apatite was formed from oxidized magma by measuring its sulfur content.
We were able measure the successfully oxygen fugacity 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 Photon Source synchrotron at Argonne National Laboratory in Illinois.
How to make oxygen from water
The magma’s sulfur content increased from around zero to around 2,000 parts per millions around 2705,000,000 years. This meant that magmas were becoming more sulfur-rich.
The Other Factors are: predominance of S6+ – a type of sulfur ion – in the apatiteIt was suggested that the sulfur came from an oxidized source. This matches The data is taken from the host zircon quartzes.
These new results show that oxidized magnesium did form during the Neoarchean era, 2.7 billion year ago. Data show that there was no dissolved oxygen in Archean oceans reservoirs to prevent the formation sulfur-rich, oxidized magnesium in subduction zones.
These magmas contain oxygen that must have been from another source. It was released into the atmosphere by volcanic eruptions.
We discovered that these oxidized magmas are associated with major gold mineralization events, both in Western Australia’s Superior Province (Western Australia) and Yilgarn Craton. This shows that there is a connection between oxygen-rich sources and the formation of world-class ore deposits.
These oxidized magmas are more important than the understanding of early Earth geodynamics. Prior to the discovery of this information, it was believed that Archean magmas couldn’t be oxidized. Ocean water Ocean floor rocks and sediments were not.
Although the exact mechanism of the magmas is not known, it is clear that they occur during subduction. This is where ocean water is transported hundreds of kilometers into the planet’s crust. This then oxidizes overlying material.
Our study shows that Archean Subduction may have been an important, yet undiscovered, factor in oxygenation of the Earth’s early days. Wheezes of oxygen from 2.7 billion years agoThe other is also available. Great Oxidation Event. This marked an increase in atmospheric carbon by two percent 2.45 to 2.2 billion years ago.
As far as we know, the Earth is the only place in the solar system – past or present – with plate tectonics and active subduction. This could partially explain why oxygen is absent on Earth and the potential for life on other rocky worlds in the future.
David Mole, Postdoctoral fellow, Earth Sciences, Laurentian University; Adam Charles Simon, Arthur F. Thurnau Professor, Earth & Environmental Sciences, University of MichiganAnd Xuyang Meng, Postdoctoral Fellow in Earth and Environmental Sciences University of Michigan
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