September 17, 2013
Researchers May Have Solved The Spin Mystery Of Earth’s Core
April Flowers for redOrbit.com - Your Universe Online
For the last 300 years at least, we have been questioning what direction the center of the earth spins. A group of scientists from the University of Leeds, UK, and the Swiss Federal Institute of Technology may have found the answer.
According to the study, published in Proceedings of the National Academy of Sciences (PNAS), the Earth's inner core - made of solid iron - "superrotates" in eastward directions. This means it spins faster than the rest of the planet. Made of mostly molten iron, the outer core spins westward at a slower pace.
Edmund Halley, who discovered Halley's comet, revealed the westward drifting motion of the planet's geomagnetic field in 1692. The current study is the first time that scientists have been able to link the way the inner core spins to the behavior of the outer core. The researchers say the Earth behaves this way because it is responding to the geomagnetic field. They hope their findings will enable scientists to interpret the dynamics of the core of the Earth, the source of our planet's magnetic field.
Relative to the Earth's surface, seismometers measuring earthquakes as they travel through the Earth's core have identified an eastward direction of the solid inner core for the last few decades.
"The link is simply explained in terms of equal and opposite action", explains Dr Philip Livermore, of the School of Earth and Environment at the University of Leeds. "The magnetic field pushes eastwards on the inner core, causing it to spin faster than the Earth, but it also pushes in the opposite direction in the liquid outer core, which creates a westward motion."
About the size of the Moon, the solid inner core is surrounded by the liquid outer core. This outer core is an iron alloy, whose convection-driven movement generates the geomagnetic field.
Scientists know that the planet's internal magnetic field changes slowly over a timescale of decades. This means that the electromagnetic force responsible for pushing the inner and outer cores will itself change over time, and may explain fluctuations in the predominantly eastward rotation of the inner core. These fluctuations were reported for the last 50 years by Tkalčić et al. and recently published in Nature Geoscience.
Based on archeological artifacts and rocks - with ages of hundreds to thousands of years, additional prior studies have suggested that the drift direction has not always been westward. Evidence suggests that some periods of eastward motion may have occurred in the last 3,000 years. When this data is viewed within the conclusions of the new model, it suggests that the inner core may have undergone a westward rotation in such periods.
The Leeds team used the giant super computer Monte Rosa, which is part of the Swiss National Supercomputing Centre in Lugano, Switzerland, to run the model of the Earth's core. A new method allowed them to simulate the Earth's core with an accuracy 100 times better than previous models.