Earth's inner core: Is it solid or liquid?

School textbooks have always maintained that the Earth's inner core is a solid sphere made up of iron. However, a recently published study in the journal Nature contradicts this by saying that it is unlikely to be solid and contains many lighter elements in it. 

Like many other things in our solar system, our own planet, Earth is filled with many mysteries that we are yet to unravel. Among them is the core of the Earth that has been attributed to many functions and has also been the subject of many queries from scientists but with its ultra-high temperatures and pressure, completely inaccessible to researchers to sample and study. 

Earth's core and earthquakes

Geologists have been using earthquake data to understand what is happening under the Earth's crust. Earlier we had reported that scientists had found hot dense structures near the inner core by studying over 30 years of earthquake data. Now, a team of researchers from China has analyzed similar data from earthquakes and run simulations to determine that the core isn't made up of solid iron but is likely to be littered with lighter elements such as silicon, sulfur, carbon, oxygen, and hydrogen. 

While this is something that other geologists have also suggested in the past, the recent study goes a step further to characterize the state of matter of these lighter elements. According to the research paper, hydrogen, oxygen, and carbon are present in a superionic state along with iron molecules. 

According to this model, these elements are neither in their solid-state or liquid state but somewhere in between, called superionic, where the iron maintains a dense hexagonal shape while the lighter elements move about in their liquid forms. The substantial decrease in wave velocities of earthquakes as they pass through the inner core can be attributed to these lighter elements, the researchers note in their publication. 

Can't explain everything

However, not everything can be explained with this model. As ABC News points out, the model cannot explain seismic anisotropy. This is a phenomenon where seismic waves travel faster through the inner core if they were to travel from the Earth's magnetic poles but are relatively slower when they travel from equator to equator.

Researcher Yu He, the first author of the study, told ABC that is likely due to the uneven distribution of these lighter elements inside the inner core where they occupy a flattened sphere-like space in the middle, slowing down the waves that pass.  He added that further studies were needed to better understand the inner core and explain such phenomenon.