We still know very little about the core itself and its motion, and we gain this knowledge by studying seismic waves passing through the center of the planet. Yi Yang and Xiaodong Song from Beijing first analyzed data from the early 1990s, and then compared them with data collected since 1964. Their analysis shows that in 2009 the rotation of the inner core almost stopped, and then it began to rotate in the opposite direction.
We believe the inner core rotates back and forth relative to the Earth’s surface, scientists say. In their opinion, the entire cycle lasts about 70 years, which means that the direction of rotation of the core changes every 35 years. Research shows that the previous change took place in the early 1970s, and the next one will take place in the mid-1940s.
Other experts, however, warn against drawing too hasty conclusions. They remind us that many things about the structure of the interior of the Earth are a mystery to us and there are numerous hypotheses regarding this matter. This is very good research done by great scientists. They used a lot of data, but in my opinion, none of the models fits well with all the data we havesays John Vidale, a seismologist at the University of Southern California. Vidale himself authored a paper last year which states that the nucleus reverses direction every six years. In his research, he relied on seismic waves generated during two nuclear explosions in the late 1960s and early 1970s. The scientist also reminds that there are data suggesting that the core rotated in the years 2001-2013, and is now almost stationary. In turn, Hrvoje Tkalcic from the Australian National University is the author of research saying that the entire cycle of changing the rotational motion of the nucleus lasts 20-30 years.
Geophysicists liken their attempts to explore the Earth’s interior to trying to study the interior of an organism without being able to dissect the patient or perform a CT scan. Some say that the inner core may contain another core. Something’s going on out there, and we’ll find out eventually. But that could take another decadesays Vidale.-
Yang and Song in their paper state that the changes in the direction of rotation of the core they observed are consistent with other observations, especially those regarding the length of the day and the planet’s magnetic field. According to them, this proves that all layers of the planet are interconnected by dynamic interactions, probably through gravitational coupling and conservation of angular momentum.