Earth is wrapped by invisible protective lines created by the churn of its core. These lines make up what's known as the magnetic field. And it has served the planet well for billions of years: It has protected Earth from the solar wind and provided a basis for navigation.
Unfortunately, it has also been weakening for about more than a century – scientists have observed flimsy regions, such as the South Atlantic Anomaly located east of Brazil, that allows for more charged solar particles to dip into the atmosphere. There's a growing concern that these regions signal a field-free Earth, in which solar particles bombard the planet unregulated, affecting life on the ground.
But scientists pointed out that the magnetic field will not go away completely, at least not for a billion years. Even if it does, the consequences will not be apocalyptic – just problematic.
Billions of years before Earth's magnetic field disappears
The molten outer core is responsible for Earth's magnetic field. Made mostly of iron and nickel, it churns and flows, powered by the convection of heat released as the inner core grows and solidifies, according to John Tarduno, a geophysicist at the University of Rochester. Tarduno's team has been studying the magnetic field and deep-Earth processes driving it.
Heat convection refers to the transfer of heat from one location to another due to the flow of a fluid, such as liquid and gas. In boiling water, for example, the hotter, lighter liquid goes up to the surface while the cooler liquid sinks to the bottom. This process propels the geodynamo, or the deep-Earth engine causing the magnetic field.
Experts note that the magnetic field will not last forever – the solid inner core is growing by about a millimeter a year, which means it will become large enough to disrupt convection in the outer core. But it's not happening any time soon.
"We're talking billions of years," said Tarduno.
Earth without a magnetic field
Tarduno's team found an anomalous eddy in the core below South Africa. It appears to cause the South Atlantic Anomaly, a known weak spot stretching 190 miles off the coast of Brazil and over much of South America. This spot isn't noticeable from the ground, but charged solar particles in this area dip down closer to Earth than usual. This has consequences for life on Earth; satellites in low orbit to Earth usually experience technical glitches when passing through the region. Meanwhile, the area's high levels of radiation can cause shooting-star visual phenomena.
Tarduno's team believes that the eddy under South Africa might have had triggered magnetic field reversals in the past, which occur when the field's north and south switch places. Scientists suspect that a reversal is preceded by a weakened magnetic field, although, in some cases, the field weakens only to regain strength.
While a world without a magnetic field is not going to be catastrophic, it will cause major problems. The conditions in the South Atlantic Anomaly may become common across the globe, causing widespread technical glitches that can disrupt radio communication and navigation. The polar lights, or auroras, will also be visible from the lower latitudes. These colorful displays occur as a result of the interaction between charged solar particles and the magnetosphere, a region of space dominated by Earth's magnetic field, rather than the magnetic field of interplanetary space. This interaction can also deplete the ozone layer, increasing people's exposure to cancer-causing ultraviolet radiation. (Related: Global magnetic anomaly hit the Earth out of nowhere during deep solar minimum.)
But Tarduno noted that during a reversal, the magnetic field does not completely go away: "[We'll] still have some magnetic field present; it just is going to be a very weak magnetic field."
Space.news has more scenarios for a field-free Earth.
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