\u201cWe believe the inner core rotates, relative to the Earth\u2019s surface, back and forth, like a swing,\u201d says experts
\n PARIS
\nFar below our feet, a giant may have started moving against us.
\nEarth\u2019s inner core, a hot iron ball the size of Pluto, has stopped spinning in the same direction as the rest of the planet and might even be rotating the other way, research suggested on Monday.
\nRoughly 5,000 kilometres (3,100 miles) below the surface we live on, this \u201cplanet within the planet\u201d can spin independently because it floats in the liquid metal outer core.
\nExactly how the inner core rotates has been a matter of debate between scientists \u2014 and the latest research is expected to prove controversial.
\nWhat little we know about the inner core comes from measuring the tiny differences in seismic waves \u2014 created by earthquakes or sometimes nuclear explosions \u2014 as they pass through the middle of the Earth.
\nSeeking to track the inner core\u2019s movements, new research published in the journal Nature Geoscience analysed seismic waves from repeating earthquakes over the last six decades.
\nThe study\u2019s authors, Xiaodong Song and Yi Yang of China\u2019s Peking University, said they found that the inner core\u2019s rotation \u201ccame to a near halt around 2009 and then turned in an opposite direction\u201d.
\n\u201cWe believe the inner core rotates, relative to the Earth\u2019s surface, back and forth, like a swing,\u201d they said.
\n\u201cOne cycle of the swing is about seven decades\u201d, meaning it changes direction roughly every 35 years, they added.
\nThey said it previously changed direction in the early 1970s and predicted the next about-face would be in the mid-2040s.
\nThe researchers said this rotation roughly lines up with changes in what is called the \u201clength of day\u201d \u2014 small variations in the exact time it takes Earth to rotate on its axis.
\nStuck in the middle
\nSo far there is little to indicate that what the inner core does has many effects on surface dwellers.
\nBut the researchers said they believed there are physical links between all of Earth\u2019s layers, from the inner core to the surface.
\n\u201cWe hope our study can motivate some researchers to build and test models which treat the whole Earth as an integrated dynamic system,\u201d they said.
\nExperts not involved in the study expressed caution about its findings, pointing to several other theories and warning that many mysteries remain about the centre of the Earth.
\n\u201cThis is a very careful study by excellent scientists putting in a lot of data,\u201d said John Vidale, a seismologist at the University of Southern California.
\n\u201c(But) none of the models explain all the data very well in my opinion,\u201d he added.
\nVidale published research last year suggesting the inner core oscillates far more quickly, changing direction every six years or so. His work was based on seismic waves from two nuclear explosions in the late 1960s and early 1970s.
\nThat timeframe is around the point when Monday\u2019s research says the inner core last changed direction \u2014 which Vidale called \u201ckind of a coincidence\u201d.
\nGeophysicists \u2018divided\u2019
\nAnother theory \u2014 which Vidale said has some good evidence supporting it \u2014 is that the inner core only significantly moved between 2001 to 2013 and has stayed put since.
\nHrvoje Tkalcic, a geophysicist at the Australian National University, has published research suggesting that the inner core\u2019s cycle is every 20 to 30 years, rather than the 70 proposed in the latest study.
\n\u201cThese mathematical models are most likely all incorrect because they explain the observed data but are not required by the data,\u201d Tkalcic said.
\n\u201cTherefore, the geophysical community will be divided about this finding and the topic will remain controversial.\u201d
\nHe compared seismologists to doctors \u201cwho study the internal organs of patients\u2019 bodies using imperfect or limited equipment\u201d.
\nLacking something like a CT scan, \u201cour image of the inner Earth is still blurry\u201d, he said, predicting more surprises ahead.
\nThat could include more about a theory that the inner core might have yet another iron ball inside it \u2014 like a Russian doll.
\n\u201cSomething\u2019s happening and I think we\u2019re gonna figure it out,\u201d Vidale said.
\n\u201cBut it may take a decade.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"
\u201cWe believe the inner core rotates, relative to the Earth\u2019s surface, back and forth, like a swing,\u201d says experts PARIS Far below our feet, a giant may have started moving against us. Earth\u2019s inner core, a hot iron ball the size of Pluto, has stopped spinning in the same direction as the rest of the […]<\/p>\n","protected":false},"author":2,"featured_media":309258,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[],"class_list":["post-309238","post","type-post","status-publish","format-standard","has-post-thumbnail","category-world"],"yoast_head":"\n