The Weakening Earth‘s Magnetic Field

Earth’s magnetic field doesn’t just give us our north and south poles; it’s also what protects us from solar winds and cosmic radiation – but this invisible force field is rapidly weakening, which has been lasting more than one thousand years, according to a new research.

Scientists think it could actually flip, with our magnetic poles reversing. As crazy as that sounds, this actually does happen over vast stretches of time. The last time it occurred was about 780,000 years ago. When it takes place, it’s not quick, with the polarity reversal slowly occurring over thousands of years. Nobody knows for sure if another such flip is imminent, and one of the reasons for that is a lack of hard data.

The region that concerns scientists the most at the moment is called the South Atlantic Anomaly – a huge expanse of the field stretching from Chile to Zimbabwe. The field is so weak within the anomaly that it’s hazardous for Earth’s satellites to enter it, because the additional radiation it’s letting through could disrupt their electronics. One of the reasons scientists don’t know much about the magnetic history of this region of Earth is it lacks what’s called archaeomagnetism data – physical evidence of magnetism in Earth’s past, preserved in archaeological relics from bygone ages.

One such bygone age belonged to a group of ancient Africans, who lived in the Limpopo River Valley – which borders Zimbabwe, South Africa, and Botswana: regions that fall within the South Atlantic Anomaly of today.

Approximately 1,000 years ago, these Bantu peoples observed an elaborate, superstitious ritual in times of environmental hardship. During times of drought, they would burn down their clay huts and grain bins, in a sacred cleansing rite to make the rains come again – never knowing they were performing a kind of preparatory scientific fieldwork for researchers centuries later. When the clay was burnt at very high temperatures, the magnetic minerals became stable; and when they cool from these very high temperatures, they lock in a record of the earth’s magnetic field.

Evidence suggested that these anomalies have happened in the past. Therefore, the weakening in the South Atlantic Anomaly isn’t a standalone phenomenon of history. Similar fluctuations occurred in the years 400-450 CE, 700-750 CE, and 1225-1550 CE – and the fact that there’s a pattern tells us that the position of the South Atlantic Anomaly isn’t a geographic fluke. Stronger evidence showed that there’s something unusual about the core-mantel boundary under Africa that could be having an important impact on the global magnetic field.

The current weakening in Earth’s magnetic field – which has been taking place for the last 160 years or so – is thought to be caused by a vast reservoir of dense rock called the African Large Low Shear Velocity Province, which sits about 2,900 kilometers (1,800 miles) below the African continent. This dense region, existing in between the hot liquid iron of Earth’s outer core and the stiffer, cooler mantle, is suggested to somehow be disturbing the iron that helps generate Earth’s magnetic field.

There’s a lot more research to do before we know more about what’s going on here.