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

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)

• • 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.