Geology
The Earth’s interior could contain more than three times the amount of water present in all our oceans combined, existing within the structures of silicate minerals that are stable at the prevailing conditions deep inside the Earth. New research has helped to elucidate how deep water can be transported into the Earth’s interior. We spoke to Carmen Sanchez-Valle of ETH Zürich about the methods involved in collecting this data, as well as the implications behind these findings
Shedding light into deep waters
Water is fundamental for processes that occur at the Earth’s surface, but it also plays a critical role in many geological processes occurring deep inside of the earth that shape its evolution. Small amounts of water incorporated into the structure of minerals have a major effect on their stability, behaviour and phase equilibria. Global processes
such as mantle convection,
deformation and melting behaviour are strongly influenced by the activity of water that also fuels plate tectonics. Naturally occurring
catastrophic events, earthquakes and volcanic such as eruptions, are
influenced or triggered by the behaviour of these hydrous components contained within minerals. Carmen Sanchez-Valle, assistant professor of experimental geochemistry and mineral physics at the Swiss Federal Institute of Technology, Zurich, has worked with her team to develop several novel analytical techniques to investigate this environment. “Through learning about the Earth’s interior,
phases are decomposed due to the high pressure and temperature of
the Earth’s
interior. Much of this water returns to the surface by volcanism, but a large fraction of is retained in newly formed high pressure hydrous phases
Figure 1: Close view of a diamond anvil cell used to reproduce the pressure- temperature conditions of the Earth’s interior in the laboratory.
we become more aware of what actually occurs on the surface,” she explains. Water
is
higher depths, opening the possibility for water to recirculate deeper into the mantle beyond 400 km depth. However, the exact amount of water stored in the solid Earth, and how (and how much) of this water is recycled obscure.
back to the surface, These questions are key to reintroduced into the Earth’s
interior by hydrated tectonic (oceanic) plates that return into the mantle in subduction zones, and released when hydrous minerals/
understanding the inner and surface evolution of planet Earth. “It’s difficult, but also a very important challenge for us to try and quantify how much water could be contained there, and how it might be distributed back to the surface,” says Sanchez-Valle. Because these processes typically take
place hundreds of kilometres beneath the surface of the Earth, obtaining samples is
Figure 2: Experimental setup using a
green laser light to measure the speed of seismic waves in Earth materials (“indoor seismology”).
that are stable at much remains
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