amount of oxygen Earth’s atmosphere makes it a habitable planet.
21% of the atmosphere consists of this life-giving element. But in the distant past — since modern times, 2.8 to 2.5 billion years ago — This oxygen was almost absent.
So how did Earth’s atmosphere become oxygenated?
Our researchPosted in Natural Sciences Earth Sciencesadds a tantalizing new possibility: that at least some of Earth’s primordial oxygen came from a tectonic source from the movement and destruction of the Earth’s crust.
Archean country
The Archean eon represents a third of our planet’s history, from 2.5 billion years ago to the last four billion years.
This strange land was a covered water world green oceanswrapped methane haze, and completely lacks multicellular life. Another strange aspect of this world is the nature of its tectonic activity.
On the modern Earth, the dominant tectonic activity is called plate tectonics, in which oceanic crust – the outermost layer of land under the oceans – sinks into the earth’s mantle (the region between the earth’s crust and the core) at meeting points called subduction zones. However, there is much debate as to whether plate tectonics made a comeback in the Archean era.
A feature of recent subduction zones is their connectivity oxidized magma. This magma forms when oxidized sediments and bottom water — cold, dense waters — form near the ocean floor. inserted into the cloak. This produces magma with a higher oxygen and water content.
Our research aims to verify whether the absence of oxidants in archaic bottom waters and sediments can prevent the formation of oxidized 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 2,750-2,670 million-year-old granite rocks from 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 allowed us to examine the oxidation level of magma generated in the new era.
Measuring the oxidation state of these igneous rocks, formed by the cooling and crystallization of magma or lava, is a challenge. Post-crystallization events may have changed these rocks through deformation, burial, or subsequent heating.
So we decided to take a look at mineral apatitelocated in zircon crystals in these rocks. Zircon crystals can withstand extreme temperatures and stresses from 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 – the size of a human skin cell – are trapped inside the zircon crystals. contain sulfur. By measuring the amount of sulfur in apatite, we can determine whether the apatite grew from oxidized magmas.
We managed to measure escape oxygen of the original Archean magma – which is basically how much free oxygen is in it – using a specialized technique called X-ray absorption spectroscopy near the edge structure (S-XANEN) to the advanced synchrotron photon source Argonne National Laboratory in Illinois.
extract oxygen from water?
We found that the sulfur content of the magma, which was initially zero, increased to 2,000 ppm about 2,705 million years ago. This indicates that the magma has become rich in sulfur. also the Predominance of S6+ – a type of sulfur ion – in apatite He suggested the sulfur came from an oxidized, identical source Data from host zircon crystals.
These new findings indicate that oxidized magmas formed in modern times, 2.7 billion years ago. The data show that the lack of dissolved oxygen in archaic reservoirs did not prevent the formation of sulfur-rich oxidized magmas in subduction zones. The oxygen in this magma must have come from some other source and eventually entered the atmosphere during volcanic eruptions.
We found that the presence of these oxidized magmas correlates with major gold mineralization events in Upper Province and Yilgarn Crater (Western Australia), demonstrating a link between these oxygen sources and the formation of global mineral deposits.
The implications of this oxidized magma go beyond understanding the early geodynamics of the Earth. It was previously thought that Archean magma would be less likely to oxidize if it were ocean water And the Rocks or sediments on the ocean floor has not been.
While the exact mechanism is unclear, the genesis of this magma indicates that the subduction process, which carries ocean water hundreds of miles to our planet, generates free oxygen. This then oxidizes the upper mantle.
Our study shows that Archean subduction could be an unexpected vital factor in Earth’s oxygenation, early Oxygen smell 2.7 billion years ago also The Great Oxidation Event, where oxygen in the air 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 study could partly explain the lack of oxygen and ultimately life on other rocky planets in the future.
This article was originally published Conversation brings David Mol at the Laurentian University, e Adam Carlo Simone, and Xuyang Meng at the University of Michigan. Read the The original article is here.
