Probing silicates at deep-Earth conditions

Scientists have developed a way to study liquid silicates at the extreme conditions found in the Earth’s core-mantle boundary, and this, they say, could lead to a better understanding of our planet’s early molten days and maybe that of others. 

The work was a collaboration between European and US institutions, led by Guillaume Morard and Alessandra Ravasio from Sorbonne University in France, and utilised facilities including the European Synchrotron Radiation Facility in France and the SLAC National Accelerator Laboratory in California. 

The process and findings are reported in the journal PNAS.

The researchers say they first sent a shockwave through a silicate sample with a carefully tuned optical laser. 

This allowed them to reach pressures that mimic those at the Earth’s mantle – 10 times higher than previously achieved with liquid silicates – and temperatures as high as 6000 Kelvin, slightly hotter than the surface of the Sun.

Next, they hit the sample with ultrafast X-ray laser pulses at the precise moment the shockwave reached the desired pressure and temperature. Some of the X-rays then scattered into a detector and formed a diffraction pattern. 

The atomic structure of materials is often unique, and diffraction patterns revealed that “fingerprint”, allowing the researchers to follow how the sample’s atoms rearranged in response to the increase of pressure and temperature during the shockwave. 

They compared their results to those of previous experiments and molecular simulations to reveal a common evolutionary timeline of glasses and liquid silicates at high pressure.

“We’re still trying to piece together how the Earth actually started to form, how it transformed from a molten planet to one with living creatures walking around on its silicate mantle and crust,” says SLAC scientist Arianna Gleason. 

“Learning about the strange ways materials behave under different pressures can give us some hints.”

The next step will be to perform experiments at higher X-ray energies to make more precise measurements of the atomic arrangement of liquid silicates. 

The researchers also hope to reach higher temperatures and pressures to gain insight into how these processes unfold in planets bigger than Earth, and how the size and location of a planet influences its composition.

“As of this month, more than 4000 exoplanets have been discovered, about 55 of which are positioned in the habitable zone of their stars where it’s possible for liquid water to exist,” says Gleason. 

“Some of those have evolved to the point where we believe there’s a metallic core that could generate magnetic fields, which shield planets from stellar winds and cosmic radiation.