Geologists and seismologists led by James Badro of the Institut de Physique du Globe de Paris reported proof that oxygen is the only light element in the Earth’s core. The research was published in the May 12, 2014, edition of the journal Proceedings of the National Academy of Sciences. This is the first definite proof of a light element being a part of the Earth’s core.
The Earth's core is known to be composed of iron and as much as five percent nickel. Seismic sensing stations positioned around the globe have detected the transfer of the energy produced by volcanic eruptions, tsunamis, earthquakes, and other geological movements in the Earth’s surface through the Earth’s core. The rate of transfer of the seismic waves produced by events at the Earth’s surface is an indication of the composition of the Earth’s core.
Previous scientific work and samples from the upper mantle of the Earth have reduced the potential candidates that compose the core to iron, nickel, sulfur, silicone, oxygen, or carbon. Seismic readings have indicated that the core is not composed of iron alone. The exact composition of the Earth’s core has been unknown until now.
The researchers prepared mixtures of iron, nickel, and combinations of sulfur, silicone, carbon, and oxygen in the laboratory. The mixtures were heated to temperatures that are similar to the temperature of the Earth’s core. The mixtures were examined to determine what mixture produced the same rate of transfer of seismological waves as the Earth’s core. The only combination that produced similar rates of seismic wave transfer contained between three percent and six percent oxygen.
This research is consistent with the known composition of the Earth’s mantle. The lower mantle contains iron oxide. The presence of oxygen in the core, as proved experimentally, is indicative of an equilibrium transfer between the core and the deepest part of the mantle.