Earth’s magnetic field, also known as the geomagnetic field, is the magnetic field that extends from the Earth’s interior to where it meets the solar wind, a stream of charged particles emanating from the Sun. Its magnitude at the Earth’s surface ranges from 25 to 65 microtesla(0.25 to 0.65 gauss). Roughly speaking it is the field of a magnetic dipole currently tilted at an angle of about 10 degrees with respect to Earth’s rotational axis, as if there were a bar magnet placed at that angle at the center of the Earth. Unlike a bar magnet, however, Earth’s magnetic field changes over time because it is generated by a geodynamo.
Earth’s last magnetic reversal took place 786,000 years ago and happened very quickly, in less than 100 years — roughly a human lifetime. The rapid flip, much faster than the thousands of years most geologists thought, comes as new measurements show the planet’s magnetic field is weakening 10 times faster than normal and could drop to zero in a few thousand years.
Earth’s magnetic field is constantly shifting, and roughly every 200,000 to 300,000 years it flips north and south completely. We’re currently overdue for a switcheroo—and scientists now say it could happen in a time as short as 100 years, potentially altering life in unexpected ways.
A study demonstrates that Earth’s last magnetic reversal – 786,000 years ago – happened in roughly the span of a human lifetime.
How did they discern changes in the magnetic field that date back hundreds of thousands of years? By testing layers of ash deposited by volcanic eruptions over the course of 10,000 years, found in a lakebed near Rome. According to a release from Berkeley, the magnetic field directions are “frozen” into these layers of ash, which could be reliably dated to find out when the reversals occurred and how long they took to complete. “We don’t know whether the next reversal will occur as suddenly as this one did, but we also don’t know that it won’t,” said Berkely’s Paul Renne, one of the study’s authors.
We’ve known for a long time that the Earth’s magnetic field is shifting, We know, for example, that the North Pole has moved 600 miles in the last 200 or so years. We also know that, as observed by three ESA satellites this summer, the Earth’s magnetic field is weakening in some areas and strengthening in others. We also know that the shifting currents are already necessitating some changes in our human world: Airports that name their runways after compass directions have recently been forced to rename and repaint due to the shift.
For us short-lived humans, these changes are normally unthinkably geologic in scale. It’s fascinating to learn that though we likely won’t be witness to a shift of this magnitude, it’s within the realm of possibility that some other homo sapiens might.