MessageToEagle.com – As Earth’s magnetic shield fails, so do its satellites. First, our communications satellites in the highest orbits go down. Next, astronauts in low-Earth orbit can no longer phone home. And finally, cosmic rays start to bombard every human on Earth.
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. If Earth’s magnetic field were to decay significantly, it could collapse altogether and flip polarity – changing magnetic north to south and vice versa. The consequences of this process could be dire for our planet.
‘The geomagnetic field has been decaying for the last 3,000 years,’ Dr Nicolas Thouveny from the European Centre for Research and Teaching of Environmental Geosciences (CEREGE) in Aix-en-Provence, France, said in a press release.
‘If it continues to fall down at this rate, in less than one millennium we will be in a critical (period).’
Cosmic rays
Our planet’s magnetic field is predominantly created by the flow of liquid iron inside the core. It has always been a feature of our planet, but it has flipped in polarity repeatedly throughout Earth’s history. 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.
By 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. 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.
For a polarity reversal to occur, the magnetic field needs to weaken by about 90% to a threshold level. 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.
When this happens, these cosmic rays collide with more and more atoms in our atmosphere, such as nitrogen and oxygen. This produces variants of elements called cosmogenic isotopes, such as carbon-14 and beryllium-10, which fall to the surface. And by studying the quantities of these in cores, we can see when polarity reversals took place.
The last reversal occurred between 772,000 and 774,000 years ago. 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. This is when we are most at risk – as the field decays and then recovers its strength. The last excursion occurred 40,000 years ago, and evidence suggests we are heading in that direction again.
‘The geomagnetic field has been losing 30 percent of its intensity in the last 3,000 years,’ said Dr Thouveny. ‘From this value, we predict it will drop to near zero in a few centuries or a millennia.’
The effects of a weakened magnetic field are seen on our satellites in orbit. 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.
This is called the South Atlantic Anomaly (SAA), and the CoreSat project led by Professor Chris Finlay from the Technical University of Denmark (DTU) near Copenhagen is trying to figure out what is causing the SAA.
‘This is a region where we see that satellites consistently (experience) electronic failures,’ said Prof. Finlay. ‘And we don’t understand where this weak field region is coming from, what’s producing it, and how it might change in the future.’
Scientists first noticed the SAA in the 1950s, and since then it has decreased in strength by a further 6%, as well as moving closer to the west. ‘(There) hasn’t really been any convincing explanation of it,’ said Prof. Finlay, adding that scientists haven’t been able to predict how it’s going to alter.
The CoreSat project is hoping to change all that, using the most detailed data available yet to study the properties of the magnetic field here and how it shifts over time. By probing the SAA, the team are hoping to see what’s going on inside Earth’s core that might be causing it.
MessageToEagle.com