New research indicates that nitrogen, one of the most-common elements in the Universe and the dominant gas in the atmosphere of Earth, becomes a metallic fluid when subjected to the extreme pressure and temperature conditions found deep inside the Earth and other planets.
“Nitrogen could get into the Earth’s mantle when one tectonic plate slides beneath another — a process called subduction — and could even make its way into the iron-rich core as an impurity, or it could be a remnant from Earth’s formation that didn’t escape via volcanic activity to form the proto-atmosphere in Earth’s babyhood,” said Dr. Shuqing Jiang, a researcher at the Carnegie Institution of Washington and the Institute of Solid State Physics, Chinese Academy of Sciences.
In Earth’s atmosphere, nitrogen is most-commonly bonded with itself in so-called diatomic (N2) molecules.
Calculations indicate that at extreme pressures and temperatures, such as those found deep inside pur planet, nitrogen should transform from an insulating (non-electrically conductive) diatomic molecule to a metallic (electrically conductive) fluid polymer, comprised of atoms linked by complex molecular bonds.
Previous experiments showed evidence of diatomic nitrogen molecules disassociating and changing states under extreme pressures and temperatures, but a greater range of conditions needed to be explored.
Dr. Jiang and colleagues set out to probe these extreme-condition transitions using a diamond anvil cell and high energy laser beams.
They were able to observe how samples of nitrogen behaved at more than one million times normal atmospheric pressure and temperatures above 5,400 degrees Fahrenheit (3,000 degrees Celsius).
Their observations confirmed that, under such conditions, nitrogen exists as a liquid metal.
“This means that, theoretically, nitrogen would remain in its diatomic state in the Earth’s mantle but would disassociate into a fluid metal in or just above the core, which potentially has implications for our understanding of the planet’s deep nitrogen cycle,” said Dr. Sergey Lobanov, from the Carnegie Institution of Washington, GFZ German Research Centre for Geosciences and Stony Brook University.
“Our findings could inform the efforts to create forms of energetic nitrogen polymers as well as superconducting, metallic states of a sister diatomic molecule, hydrogen, which could revolutionize the energy sector if reliably synthesized,” said Dr. Nicholas Holtgrewe, from the University of Chicago.
“Earth’s atmosphere is the only one of all the planets where nitrogen is the main ingredient — greater even than oxygen,” said Dr. Stewart McWilliams, from the University of Edinburgh and the Carnegie Institution of Washington.
“Our study shows this nitrogen could have emerged from deep inside the planet.”