2nd December 2022 (7 Topics)
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A New study hints at the source of Earth’s Oxygen
Context
A study published in Nature Geoscience suggests that at least some of the Earth’s early oxygen came from a tectonic source via the movement and destruction of the Earth’s crust.
The Archean Earth
- The Archean eon represents one-third of our planet’s history, from 2.5 billion years ago to four billion years ago.
- Its Features:
- This alien Earth was a water-world
- It was covered in green oceans (Green Rust-an Iron Mineral)
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Source of earth’s Iron ore deposits:
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- Its atmosphere was shrouded in a methane haze
- The atmosphere was without oxygen
- It completely lacked multi-cellular life.
- Life was limited to simple single-celled organisms lacking nuclei, called
- Another alien aspect of this world was the nature of its tectonic activity.
The link between plate tectonics and oxygen formation:
- The outermost layer of the Earth under the oceans sinks into the Earth’s mantle at points of convergence called subduction zones.
- As the plate sinks deeper, the temperature around becomes so hot that the crust releases fluids trapped inside, and this results in the formation of
- Oxidized Magmas are formed when oxidized sediments and bottom waters — cold, dense water near the ocean floor — are introduced into the Earth’s mantle.
- This produces magma with high oxygen and water content.
What is the Question?
- It aims to find out if the absence of oxidized materials in Archean bottom waters and sediments could prevent the formation of oxidized magmas.
- The identification of such magmas in Neoarchean magmatic rocks can bring light to the tectonics activities that occurred 2.7 billion years ago.
Creating oxygen from water
- In the experiment, it is found that the content of sulfur in the magma increased from zero to 2000 parts per million around 2705 million years.
- This indicated the magma had become more sulfur-rich.
- It is further ensured that the sulfur was from an oxidized source matching the data from the host zircon crystals.
- It indicates that oxidized magmas did form in the Neoarchean era 7 billion years ago.
These new findings indicate that
- The lack of dissolved oxygen in the Archean Ocean reservoirs did not prevent the formation of sulfur-rich, oxidized magmas in the subduction zones.
- The oxygen in these magmas must have come from another source and was ultimately released into the atmosphere during volcanic eruptions.
Significance:
- The study goes beyond the understanding of early Earth geodynamics.
- Archean subduction could have been a vital factor in the oxygenation of the Earth.
- This study could partly explain the lack of oxygen and, life on the other rocky planets in the future as well.
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