The drilling of a 270,000-year-old core from a Tasmanian lake set the first Australian record of a major global event where the Earth’s magnetic field ‘switched’ – and the opportunity to set a precedent for the development of new paleomagnetic dating tools for Australian archeology and paleo sciences.
“This is the first study of its kind in Australia since pioneering studies in the 1980s,” said author Dr Agathe Lisé-Provonost, a McKenzie Fellow of the School of Earth Sciences at the University of Melbourne.
‘Only two lakes in Northeastern Australia have previously produced such a’ full-vector ‘record, where both the previous directions and the intensity of the earth’s magnetic field were obtained from the same core. ‘
Published in the journal Quaternary geochronology, Chronostratigraphy of a sediment record of 270 ka from Lake Selina, Tasmania: a combination of radiometric, geomagnetic and climatic dates, describes how drilling in the 5.5 meter long Lake Selina core that 41,000 years ago people in Tasmania spectacular auroras must have been seen when the Earth’s magnetic field turned around, and for several thousand years was north south and south north.
“During the geomagnetic ‘excursion’, the strength of the Earth’s magnetic field almost disappeared,” said DrLisé-Provonost.
‘This will lead to a huge increase in cosmic and solar particles bombing our planet because the magnetic field normally acts like a shield.
“We do not know when the next geomagnetic outing will take place, but if one were to take place today, satellites would be rendered useless, smartphone navigation programs would fail, and there would be major disruptions to power distribution systems.”
Research that led to the discovery began in 2014 when the author traveled to a small subalpine lake in western Tasmania with a team led by associate professor Michael-Shawn Fletcher, where a temporary floating platform leading to two inflatable rafts were tied, used for drilling. in the sediment.
With the core containing a climate, vegetation and paleomagnetic record of the area, the team looked to first accurately date its layers and find evidence of the changes in the ecosystem that occurred when Tasmanian Aboriginals arrived 43,000 years ago and ruled the country for thousands of years. There is also evidence of sudden changes that have taken place since the arrival of Europeans 200 years ago.
“Magnetic particles are eroded from rocks, by wind or water to a lake, and settle on the bottom of the lake,” said Dr Lisé-Provonost.
‘The magnetic particles act like small compass needles and line up with the Earth’s magnetic field. As these particles accumulate and are buried, they are locked in place, leaving a history of the Earth’s magnetic field. The deeper we drill, the further back in time we go. ‘
It is hoped that the research will lead the way for more studies on the geomagnetic field behavior of Australian lakes and other geological materials, such as lava flows, cave deposits and archaeological artifacts, to develop new paleomagnetic dating tools and improve Earth’s magnetic field models. to one day perhaps predict the next geomagnetic outing.
The research team will now go even further back in restoring Tasmania’s climatic history, analyzing sediments from the 816,000-year-old meteorite impact at Darwin Crater.
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