amount of oxygen Earth’s atmosphere makes it a habitable planet.
21% of the atmosphere consists of this life-giving element. But far back in the past – up to the modern era, 2.8 to 2.5 billion years ago – This oxygen is almost non-existent.
So how did Earth’s atmosphere become oxygenated?
our researchPosted in Natural Sciences of the Earthadds a tantalizing new possibility: that at least some of Earth’s primordial oxygen came from tectonic sources through crustal movement and breaking.
Archean land
The Archean Aeon represents a third of our planet’s history, from 2.5 billion years ago to the last four billion years.
This strange land is a closed water world green oceanwrapped methane fog, and completely devoid of 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, where oceanic crust – the outermost layer of land under the oceans – dips into the earth’s mantle (the area between the earth’s crust and the core) at points of meeting called subduction zones. However, there is much debate whether plate tectonics reappeared in the Archean era.
One of the recent features of subduction zones is their connectivity oxidized magma. This magma forms when sediments oxidize and bottom waters, cold, dense waters, form near the ocean floor. inserted into the earth’s mantle. This produces magma with a higher oxygen and water content.
Our research aims to verify whether the absence of oxidants in the bottom waters and Archean sediments can prevent the formation of oxidized magma. The identification of these magmas in the new igneous rocks may provide evidence that subduction and plate tectonics occurred 2.7 billion years ago.
Experience
We collected granite rock samples between 2,750 and 2,670 million years old from across the Upper Province’s Abetepe Wawa subdistrict, the largest preserved Archean continent that stretches 2,000 kilometers from Winnipeg, Manitoba, to far eastern Quebec. This allows us to study the oxidation rates of magmas produced during the new era.
Measuring the oxidation state of these igneous rocks, which are formed through the cooling and crystallization of magma or lava, is a challenge. Post-crystallization events may have altered these rocks through subsequent deformation, burial, or heating.
So, we decided to check it out mineral apatitelocated in zircon crystal on these rocks. Zircon crystals can withstand the extreme temperatures and pressures of post-crystallization events. They contain clues about the environment in which they originally formed and provide precise ages for the rocks themselves.
Tiny apatite crystals less than 30 microns wide, about the size of a human skin cell, are trapped inside the zircon crystals. contains sulfur. By measuring the amount of sulfur in apatite, we can determine whether it grew from oxidized magma.
We managed to measure escape of oxygen The original Archean magma – which is basically the amount of free oxygen contained – uses a special technique called X-ray absorption spectroscopy near the edge structures (S-XANES) in the advanced synchrotron photonic source Argonne National Laboratory in Illinois.
Producing oxygen from water?
We found that the sulfur content of the magma, which was initially around zero, increased to 2,000 ppm about 2,705 million years ago. This indicates that the magma has become rich in sulfur. A part from that, S6+ predominance – a type of sulfur ion – in apatite He suggested that the sulfur came from an identical, oxidized source Data from host zircon crystals.
The new findings suggest that oxidized magma formed in the modern era, 2.7 billion years ago. The data indicate that the lack of dissolved oxygen in Archean reservoirs does not prevent the formation of sulfur-rich oxidized magmas in subduction zones. The oxygen in this magma must have come from another source and was eventually released into the atmosphere during a volcanic eruption.
We find that the occurrence of this oxidized magma correlates with major gold mineralization events in Upper Province and Yilgarn Crater (Western Australia), indicating a link between these oxygen-rich sources and the global formation of ore deposits.
The implications of this oxidized magma go beyond understanding the early geodynamics of the Earth. Previously, Archean magma was thought to be less likely to oxidize sea water And Seabed or sedimentary rocks never.
While the exact mechanism is unclear, the appearance of this magma suggests that the process of subduction, in which seawater is carried hundreds of kilometers to our planet, produces free oxygen. This then oxidizes the upper mantle.
Our study suggests that Archean subduction could be an unexpectedly vital factor in Earth’s oxygenation, early The smell of oxygen 2.7 billion years ago likewise The Great Oxidation Event, in which atmospheric oxygen increased 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 research could partially explain oxygen starvation and, eventually, life on other rocky planets in the future.
This article was originally published Conversation by David Mol at the Laurentian University, e Adam Carlo Simone, and Xuyang Meng at the University of Michigan. Reading The original article is here.
