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A New study hints at the source of Earth’s Oxygen

  • Published
    2nd Dec, 2022
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)

Source of earth’s Iron ore deposits:

  • Billions of years ago, "green rust" formed in seawater and sank to the ocean bed, becoming a source of banded iron formations.
  • The iron in the green rust later transformed into the minerals we can now observe in the geologic record.
  • It could potentially have played an indirect role in the accumulation of oxygen in the atmosphere, called the Great Oxidation Event.
    • 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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