A study on past reversals of Earth's magnetic field has found that a rapid shift occurred within two centuries - such an event in future would increase our exposure to the Sun's radiation that may cause trillions of dollars in power and communications systems damage.

The international research team found that magnetic field reversals - whereby the magnetic south pole became the magnetic north pole and vice versa - could happen much more rapidly than the thousands of years previously thought to be needed.

Professor Andrew Roberts from The Australian National University (ANU) said the magnetic field's strength decreased by about 90 percent when a field reversal occurred, making the Earth much more vulnerable to the Sun's radiation.

"Earth's magnetic field, which has existed for at least 3.45 billion years, provides a shield from the direct impact of solar radiation," said Professor Roberts from the ANU Research School of Earth Sciences who was part of the study led by Distinguished Professor Chuan-Chou Shen at the National Taiwan University and lead author Dr. Yu-Min Chou of the Southern University of Science and Technology in China.

"Even with Earth's strong magnetic field today, we're still susceptible to solar storms that can damage our electricity-based society."

A field reversal would have much more of an effect than the solar storm that hit Earth in 1859. A similar magnitude solar storm today would cause major damage to power grids and communications systems worth trillions of dollars.

"Hopefully such an event is a long way in the future and we can develop future technologies to avoid huge damage, where possible, from such events," Professor Roberts said.

He and his ANU colleague Dr. Xiang Zhao from the Research School of Earth Sciences contributed to the study of the paleomagnetic record from 107,000 to 91,000 years ago that is based on precise magnetic analysis and radiometric dating of a stalagmite from a cave in southwestern China.

The stalagmite, which is one metre in length and eight centimetres in diameter, has a candle-like shape and ranges in colour from yellow to dark brown.

"The record provides important insights into ancient magnetic field behaviour, which has turned out to vary much more rapidly than previously thought," Professor Roberts said.

Research Report: "Multidecadally Resolved Polarity Oscillations During a Geomagnetic Excursion," Yu-Min Chou et al., 2018 Aug. 20, Proceedings of the National Academy of Sciences of the United States of America

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