© Edward Garnero and Allen McNamara
The movement of seismic waves through the material of the mantle allows scientists to image Earth's interior, just as a medical ultrasound allows technicians to look inside a blood vessel.
The movement of seismic waves through the material of the mantle allows scientists to image Earth's interior, just as a medical ultrasound allows technicians to look inside a blood vessel.
New research on oxygen and iron chemistry under the extreme conditions found deep inside Earth could explain a longstanding seismic mystery called ultralow velocity zones. Published in Nature, the findings could have far-reaching implications on our understanding of Earth's geologic history, including life-altering events such as the Great Oxygenation Event, which occurred 2.4 billion years ago.
Sitting at the boundary between the lower mantle and the core, 1,800 miles beneath Earth's surface, ultralow velocity zones (UVZ) are known to scientists because of their unusual seismic signatures. Although this region is far too deep for researchers to ever observe directly, instruments that can measure the propagation of seismic waves caused by earthquakes allow them to visualize changes in Earth's interior structure; similar to how ultrasound measurements let medical professionals look inside of our bodies.
These seismic measurements enabled scientists to visualize these ultralow velocity zones in some regions along the core-mantle boundary, by observing the slowing down of seismic waves passing through them. But knowing UVZs exist didn't explain what caused them.
However, recent findings about iron and oxygen chemistry under deep-Earth conditions provide an answer to this longstanding mystery.
It turns out that water contained in some minerals that get pulled down into Earth due to plate tectonic activity could, under extreme pressures and temperatures, split up -- liberating hydrogen and enabling the residual oxygen to combine with iron metal from the core to create a novel high-pressure mineral, iron peroxide.
Comment: The rise of oxygen caused Earth's earliest ice age