The composition of the Earth's core for years remains a mystery
Even figure out the approximate composition is very difficult. They calculate it on the basis of geochemistry and research-based history of the formation of planets in the solar system. Scientists know that the liquid core is composed mainly of iron-nickel alloy, but it is believed that small amounts of some other elements are also present in the nucleus.
Oxygen — is the most widespread element on the planet, so it is logical to assume that the oxygen might be one of the dominant "light elements" in the core. But a new study team Inveya Fei of Washington Geophysical Laboratory, Carnegie shows that the evidence of the presence of oxygen in the outer core is not present. This fact is of great importance for our understanding of the period when the Earth formed through the accretion of dust and space stuff.
Today's technology can allow to obtain samples of material from another planet, but, surprisingly, find the kernel directly is impossible. Explore the Earth's core by using seismic sounding: equipment records the reflected waves, the scientists can deduce the approximate composition of the material through which the waves pass.
According to current models, except for a large amount of ferrous materials, liquid outer core of the Earth contains a small percentage of so-called light elements — possibly, sulfur, silicon, carbon and hydrogen, and the minimum amount of oxygen. This study leads Fay in cooperation with Chinese colleagues, including lead author of the study Hayyuna Huang Wuhan University of Technology in China, which is currently working at the Carnegie. The research team received a new experimental data that narrow down the identity of the light elements present in the outer core of the Earth.
The inner core — a dense spherical formation, which is thought to have a radius of about 1200 km and consists of iron-nickel mass. It is believed that the core began to form due to cooling of the Earth's subsurface
The deeper the dive below the surface, the greater the increase and the pressure and temperature. As a result, the materials begin to work and interact differently from the way they behave on the surface. In the center of the Earth with liquid outer core and solid inner core. Scientists believe that the light elements play an important role in the convection of the liquid outer core that generates the magnetic field of the Earth.
Scientists know the changes in the function of the density and sound velocity with depth of seismic core, but until now it has been difficult to measure these properties in proposed iron-nickel alloys in the core with the temperature and pressure in a laboratory on Earth.
"We can not take a sample materials directly from the kernel. Thus, we have to simulate the conditions and learn about the properties of the materials in the core through high-tech laboratory experiments, combining modeling and seismic data, "- says Fay.
High exposure can produce shock (shock) that trigger the heat and pressure of materials simultaneously leading to the melting of materials at pressures similar to those in the outer core. The team experimented with a shock wave with the basic materials, the presence of which is expected in the core — iron mixture, sulfur and oxygen. Materials scientists have brought to a liquid state and measured their density and speed of sound passing through them under conditions that simulate conditions in the liquid core.
Comparing these data with observations, the researchers came to the conclusion that the oxygen can not be the main light elements constituting the material of the outer core, because experiments performed on oxygen-rich materials do not agree with the geophysical observations. This proves the validity of recent models of the early Earth, which was developed in a little oxidized environment.
"Research has shown the way to decode the light elements in the core. Further research should focus on synthesizing the composition of these elements, the next step will be based on finding the potential content of elements such as silicon in the outer core, "- concluded Fay.
These studies are supported by the National Natural Science Foundation of China, the Foundation of the fundamental research for universities, the National Science Foundation and the Carnegie Science Institute.