The Earth's inner core oscillates, gently swaying and swirling from one direction to another in a six-year cycle. According to recent research, this activity affects the length of the day on our planet.
As reported in the journal Science Advances, this new theory about how the Earth's interior works is at odds with previous ideas about geological layers. Previous studies have shown that the planet's deepest geological layer rotates with the rest of the planet at a slightly faster speed than the surface.
Quoted from IFL Science, Thursday (16/6/2022) Earth's inner core is a red hot ball of solid iron surrounded by a liquid outer core, then the mantle, then the Earth's crust.
In the 1990s, research showed that the Earth's inner corner undergoes a superrotation, in which the inner core rotates slightly faster than the rest of the planet. This theory is supported by research studying the waves generated from underground nuclear bomb tests conducted by the Soviet Union from 1971 to 1974 on the Novaya Zemlya archipelago, northern Russia.
In the latest study, scientists from the University of Southern California (USC) used the same methodology to study a pair of previous underground atomic tests beneath Amchitka Island at the tip of the Alaskan archipelago in 1969-1971.
Surprisingly, the results show that the inner core moved slowly in a different direction between 1969-1971, known to sub-rotate at least one tenth of a degree per year, compared to the direction it moved between 1971-1974.
"From our findings, we can see a shift in the Earth's surface compared to its inner core, as people have been suggesting for 20 years," said John E Vidale, study co-author and Dean Professor of Earth Sciences at the USC Dornsife College of Letters, Arts and Science.
He said their latest observations showed that the inner core rotated slightly more slowly from 1969-1971, then moved in the other direction from 1971-1974.
"The impermeable inner core is moving under our feet, and seems to be going back and forth a few kilometers every six years," Vidale added.
The inner workings of our planet also have a small but significant effect on the length of the day on Earth. We often think of the days on Earth as constant. In fact, the days we live can experience quite a lot of variation. About 300 million years ago, for example, a day on Earth would have lasted about 21 hours. In fact, the length of the day can vary over a decade.
The length of the day is determined by the rotational speed of the planet. This can be influenced by a number of factors, but is believed to be related to changes in the Earth's magnetic field, which is generated in the Earth's core.
The new study notes that day lengths grow and shrink as they predicted, plus or minus 0.2 seconds every six years, based on changes in Earth's inner core.
However, many questions remain. Much of this research was made possible through the data revealed by underground nuclear tests. As the number of nuclear tests has decreased significantly since the Cold War, this data is becoming increasingly scarce and scientists are forced to work with relatively inaccurate earthquake data.
Nevertheless, researchers are interested in delving deeper into the mysteries of Earth's interior architecture to better understand how and why the Earth's core behaves in strange ways.
"One of the questions we're trying to answer is, is the inner nucleus moving progressively or is it mostly locked in compared to the rest over the long term? We're trying to understand how the inner nucleus forms and how it moves over time. This is an important step in understanding this process. better," Vidale concluded.