In the Atlantic Ocean between South America and Africa, there is a vast region of Earth’s magnetic field that is about three times weaker than the field strength at the poles. Today, we can already see the effects of a weakened magnetic field on our satellites in orbit. ‘From this value, we predict it will drop to near zero in a few centuries or a millennia.’ ‘The geomagnetic field has been losing 30 percent of its intensity in the last 3,000 years,’ said Dr Thouveny. The last excursion occurred 40,000 years ago, and evidence suggests we are heading in that direction again. This is when we are most at risk - as the field decays and then recovers its strength. Since then, the field has almost reversed 15 times, called an excursion, dropping in strength significantly but not quite reaching the threshold needed before rising again. The last reversal occurred between 772,000 and 774,000 years ago. ‘The geomagnetic field has been decaying for the last 3,000 years.’ Dr Nicolas Thouveny, CEREGE And by studying the quantities of these in cores, we can see when polarity reversals took place. This produces variants of elements called cosmogenic isotopes, such as carbon-14 and beryllium-10, which fall to the surface. When this happens, these cosmic rays collide with more and more atoms in our atmosphere, such as nitrogen and oxygen. This process can take thousands of years, and during this time, the lack of a protective magnetic shield around our planet allows more cosmic rays – high-energy particles from elsewhere in the universe – to hit us.
Dr Thouveny and his team looked at two particular forms of elements that allowed them to probe the history of our planet’s magnetic field in greater detail.įor a polarity reversal to occur, the magnetic field needs to weaken by about 90% to a threshold level. Each time it flips – up to 100 times in the past 20 million years, while the reversal can take about 1,000 years to complete – it leaves fossilised magnetisation in rocks on Earth.īy taking cores - or columns - of sediments from the sea floor, like a long straw that can extend down up to 300 metres with the help of a drill, we can look back in time and see when these reversals occurred. It has always been a feature of our planet, but it has flipped in polarity repeatedly throughout Earth’s history.
Our planet’s magnetic field is predominantly created by the flow of liquid iron inside the core. Together with his colleagues, he has been investigating the history of Earth’s magnetic field, including when it has reversed in the past, and when it might again. ‘If it continues to fall down at this rate, in less than one millennium we will be in a critical (period).’ĭr Thouveny is one of the principal investigators on the five-year EDIFICE project, which has been running since 2014. ‘The geomagnetic field has been decaying for the last 3,000 years,’ said Dr Nicolas Thouveny from the European Centre for Research and Teaching of Environmental Geosciences (CEREGE) in Aix-en-Provence, France. Most worryingly, we may be headed right for this scenario. The consequences of this process could be dire for our planet. If Earth’s magnetic field were to decay significantly, it could collapse altogether and flip polarity – changing magnetic north to south and vice versa. This is a possibility that we may start to face not in the next million years, not in the next thousand, but in the next hundred.
0 kommentar(er)
