Why do the magnetic poles on Earth exist?

For a variety of reasons, Earth is exceptional in the solar system. It is the only planet with an atmosphere made of usable oxygen, it is completely covered in liquid water, and it is the only celestial body that we are aware of that supports life. However, a feature that makes our planet unique and is sometimes disregarded is the fact that Earth is the only rocky body in the inner solar system with powerful magnetic poles; a compass would be useless on Mars.

What are these poles used for and where do they come from? Let’s begin by travelling to the planet’s core in order to get the answers to these questions.

The solid inner core and the molten metal outer core are the two layers that make up the Earth’s core. Both layers are composed primarily of lighter elements like oxygen, silicon, and sulphur with a dash or two of magnetic iron and nickel.

The inner core is like a huge incandescent marble: incredibly hot and dense. However, the outer core, which is fluid, circulates its own convective current around this solid mass. According to John Tarduno, a geophysicist at the University of Rochester in New York, this ongoing convection creates the Earth’s magnetic field.

As heat continuously radiates from the inner core into the outer core, it encounters material that has been cooled by plate tectonic movement. Convection is fueled by this cycle, which also ignites the so-called geodynamo, which generates the magnetic field.

Because of the absence of plate tectonics, other planets like Mars and Venus lack magnetic fields. There is evidence that these planets may have once had self-sustaining geodynamos, but they failed for reasons that are now unknown. A modest magnetic field does exist on Mercury, but it is just 1.1% as powerful as Earth’s and does little to protect the planet from solar radiation.

The planet behaves like a massive dipolar magnet with one negatively charged pole and one positively charged pole as the liquid metal in the Earth’s outer core flows due to the planet’s velocity and high iron content. There are specific locations where the magnetic field swirls and eddies, behaving “like weather patterns that kind of float around,” Tarduno added. About 80% of the Earth’s magnetic field is organised in this way, but the other 20% is non-dipolar.

These erratic patterns result in strange magnetic field anomalies, such as the South Atlantic Anomaly, a broad region of the Atlantic Ocean where the magnetosphere’s strength sharply decreases. This “dent” in the magnetic field, according to researchers, is the result of exceptional tectonic activity under Africa. For a few reasons, regions like the South Atlantic Anomaly are both fascinating and alarming.

According to Joshua Feinberg, a geologist at the University of Minnesota who specialises in paleomagnetism, “The magnetosphere is like a protective envelope,” It serves as a sort of global sunscreen, deflecting vast amounts of harmful solar energy away from Earth. Extra doses of radiation slip through in places where the magnetosphere is weak, possibly causing a rise in the incidence of skin cancer.

The impact on satellites is “another concern,” Tarduno said. If a spacecraft is not protected by the magnetic field of Earth, solar radiation bursts known as coronal mass ejections have the potential to destroy satellites and other spacecraft. For telecommunications, internet connectivity, and GPS systems in anomaly-affected areas, this can have disastrous consequences.

The study from 2020 that was published in the journal PNAS suggests that the South Atlantic Anomaly may be 11 million years old and that pole reversal, another feature of the planetary magnetic field, may be related to it.

Ancient lava flows and deep-sea deposits contain the history of the Earth’s magnetic field. Rocks of this type are abundant in magnetic metal particles, such as microscopic iron chips, which align themselves with magnetic field lines. “Eventually, that original alignment gets locked into the sediments, and we get these deep-time records of how the Earth’s magnetic field was oriented,”, according to Feinberg.

These data have allowed scientists to determine that the magnetic poles of our planet shift throughout time. The magnetic North Pole, which is actually magnetic south at the time, is now located around 310 miles (500 km) from the physical North Pole. And according to NASA, the poles abruptly flip, inverting magnetic north and south, once every 300,000 years.

A complete pole reversal hasn’t occurred in roughly 780,000 years, according to the paleogeomagnetic record. According to some academics, this suggests that a flip is about to occur, and the strength of the South Atlantic Anomaly may be a sign that one is imminent.

The Earth’s magnetic field would weaken to 20% of its original strength if the poles were to reverse, possibly for decades. Such an occurrence would completely destabilise the current global communications infrastructure. Other studies, however, contend that a flip is not about to occur.

In any case, understanding the planet’s innards and the paleogeomagnetic record, according to Feinberg, will help us comprehend the intricate interactions between the magnetosphere and life on Earth and may even help us get ready for future change.