The rotation of the Earth’s inner core varies according to the activity of seismic waves in a six-year cycle — a cycle that also changes with the length of the day.
About 1,800 miles below our feet, the Earth’s inner core is a dense, hot ball of solid iron about the size of the dwarf planet Pluto. Because of the impossibility of direct observation, scientists studying the inner core are forced to use the interpretation of indirect measurements to determine its nature. Despite this, our understanding of the Earth’s inner core has expanded drastically over the past three decades as geologists have shown that the motion of the core changes over time.
For example, in 1996, researchers first suggested that the inner core rotate eastward, faster than the rest of the planet, at a speed of about one degree per year-a phenomenon known as “super spin.” .
However, subsequent research has shown that this may be an exaggeration.
Using a new technique, the researchers found that the inner core rotates at a rate of approximately 0.1 degrees per year, slower than previously expected.
In their new study, the researchers applied the same approach to seismic waves done by a couple of previous atomic weapons tests conducted by the United States.
Dubbed “Milrow” and “Cannikin”, these tests were conducted under Amchitka Island at the tip of the Alaska archipelago in 1969 and 1971, respectively.
By measuring compressive seismic waves from nuclear explosions, the team concluded that the inner core rotates in the opposite direction to the rest of the planet and “slightly rotates” at least 0.1 degrees per year. This is the first time that the hypothesis that the internal core circulation is subject to six years of oscillations has been confirmed by direct seismic observation.
Oscillations are regular variations around a central point-similar to the movement of a pendulum on a long clock.
The researchers explained that the changes would be visible compared to the inner core of the Earth’s surface, as people have confirmed for 20 years. Recent observations, however, suggest that the internal core was slightly slower between 1969 and 1971 and then moved in the other direction from 1971 to 1974.
The length of the day changes plus or minus 0.2 seconds every six years-a fluctuation that is offset by differences in the Earth’s magnetic field.
The full results of the research were published in the journal Science Advances.
Source: Express
Source: Arabic RT
