The Earth's atmosphere has enough oxygen to make it a good place to live.
This life-giving element makes up 20% of the atmosphere. Oxygen was almost absent in the past, as far back as the Neoarchean era.
Earth's atmosphere became oxygenated.
It is possible that some of the Earth's early oxygen came from the movement and destruction of the Earth's crust.
The Earth of the Archeans.
The Archean eon spans 2.5 billion years ago to four billion years ago.
The alien Earth was covered in green oceans and lacked multi-cellular life. The nature of the earth's tectonic activity was alien to this world.
Plate tectonics is where the outer layer of the Earth under the ocean sinks into the Earth's mantle. There is a lot of debate over whether plate tectonics existed in the Archean era.
Modern subduction zones are associated with oxidation magmas. When cold, dense water near the ocean floor is introduced into the Earth's mantle, it causes the formation of these magmas. The magmas have high oxygen and water content.
We wanted to see if the absence of oxidation in Archean bottom waters could prevent the formation of oxidation. Evidence of subduction and plate tectonics could be provided by the identification of such magmas.
We collected samples from across the Abitibi-Wawa subprovince of the Superior Province. We were able to investigate the level of oxidation of magmas.
It's difficult to measure the oxidation-state of these magmatic rocks. These rocks may have been altered by post-crystallization events.
We looked at the mineral apatite which is present in the rocks. The post-crystallization events can be very intense. Clues about the environments in which they were originally formed are retained.
The small apatite crystals are trapped in the zircon crystals. Sulfur is contained in them. If we measure the amount of sulfur in apatite, we can determine if the apatite grew from an oxidation.
We were able to measure the oxygen fugacity of the original Archean magma using a special technique called X-ray Absorption Near Edge Structure Spectroscopy.
Oxygen can be created from water.
The magma sulfur content went from zero to 2000 parts per million in 2 700 million years. The magmas were more sulfur-rich. The predominance of S6+ in the apatite suggested that the sulfur was from an oxidizer.
The findings show that oxidation formed in the Neoarchean era. The data shows that the lack of dissolved oxygen in the ocean didn't prevent the formation of sulfur-rich magmas. During volcanic eruptions, the oxygen in these magmas must have come from somewhere else.
There is a correlation between the occurrence of oxidation magmas and gold occurrences in the Superior Province and Yilgarn Craton.
The implications of these magmas go far beyond what we know about Earth's geology. When the ocean water and ocean floor rocks were not present, it was thought that Archean magmas wouldn't be able to oxidize.
The process of subduction, where ocean water is taken hundreds of kilometers into our planet, is believed to generate free oxygen. The mantle is oxidized by this.
The Great Oxidation Event, which marked an increase in atmospheric oxygen by two percent, could have been caused by Archean subduction.
The Earth is the only place in the solar system with plate tectonics. The lack of oxygen on the other rocky planets could be explained by this study.
There is more information about the formation of sulfur-rich magmas in the Neoarchaean subduction zone.
Journal information: Nature Geoscience
Under a Creative Commons license, this article is re-posted. The original article is worth a read.
All Rights Reserved © 2024
