- The Earth has very less amount of xenon than it should, and the reason behind this is still unclear.
- A new study suggests that it might be buried under the Earth’s core.
- Under high temperatures and pressure, Xenon might have reacted with metals present in Earth’s core to form different compounds.
Metallic elements found on the surface of the Earth are usually electropositive and tend to lose their valence electron to create positively-charged ions. At normal pressure and temperature, metals containing free electrons create compounds with electronegative elements. For instance, Nickel reacts with oxygen to create Nickel oxide (NiO), which is mainly used in alloy production.
Noble gas elements, on the other hand, like Xenon and, are very less reactive (almost none under normal pressure and temperature) with other elements.
In the Earth’s core, however, these highly chemically-inert elements react with other metals in a very unique way. Scientists at Lawrence Livermore National Laboratory have studied the possible reaction between nickel and iron with xenon at very high temperature and pressure, similar to what’s found in Earth’s core.
Mystery of Earth’s Xenon
The Xenon on Earth is missing. According to numerous old studies, our atmosphere consists of very less xenon that it should. However, this new research indicates that it might be buried deep under the Earth’s core.
In this planetary system, Carbonaceous chondrites contain the most known primitive materials. They are mostly made of materials that formed the Earth. The mysterious thing is Carbonaceous chondrites have way more Xenon than our planet and atmosphere. Because Xenon is a noble gas element, it should not have reacted with other elements to form different compounds.
Researchers have simulated an Earth-core-like environment, where they targeted nickel and iron-xenon reactions at temperatures more than 2000 Kelvin and pressures above 2 million times the Earth’s atmospheric pressure.
The team used Raman spectroscopy and X-ray diffraction to figure out the chemical makeup of a compound and tell if the metals and noble gas were reacting. They used a natural iron meteorite (from Sikhote-Alin mountain, Russia) as a proxy to composition of Earth’s core.
They found a sign of a reaction between nickel/iron with xenon through a diffraction pattern in X-ray beamline. When xenon is crushed by intense pressures at very high temperatures, its chemical properties are changed, enabling it to react with other elements and create compounds. In this way, xenon remains hidden within other elements.
Heavy noble gas elements, such as xenon, are known to react with strong electronegative elements like halogens. However, this is the first research that shows the signature of metals reacting with noble gas element.
These outcomes suggest that altering element’s chemical properties, under intense surrounding could make an element electronegative (which is electropositive at normal conditions). This means they had a very strong affinity to snatch electrons that are supposed to stray into their orbit. The electronegativity was so powerful, that it plucked the electron from noble gas elements.
Furthermore, the atmosphere of Mars is also depleted in xenon. While the Martian core pressure is nearly 40 GPa (compared to Earth’s 50 GPa), it’s plausible to consider that xenon depletion likely stems from the similar process for both planets. It indicates that XeFe3 formation is an unlikely explanation of missing xenon paradox.
According to the research team, there is a need of a novel periodic table for better understanding of element’s chemical properties that change under intense thermodynamics conditions. There are still tons of paradoxes and systems to resolve. Scientists plan to write new chapters about intense physicochemical events.