The geomagnetic field around planet Earth.
Albert Einstein described the origin of Earth’s magnetic field as one of the most intriguing mysteries of the planet. We now know that Earth’s outer core consists of a liquid iron-nickel alloy. Earth’s rotation sets this liquid in motion, generating an electric current and a magnetic field. Yet scientists can’t still explain how exactly this works, and even more puzzling, why Earth’s magnetic field can change in intensity over time and even switch direction, meaning the magnetic North and South Pole flip locations.
New research analyzing pieces of the most ancient rocks on the planet adds some of the sharpest evidence yet that Earth’s crust was pushing and pulling in a manner similar to modern plate tectonics at least 3.25 billion years ago. The study also provides the earliest proof of when the planet’s magnetic poles swapped places.
The two results offer clues into how such geological changes may have resulted in an environment more conducive to the development of life on the planet.
The work, led by Harvard geologists Alec Brenner and Roger Fu, focused on a portion of the Pilbara Craton in western Australia, one of the oldest and most stable pieces of the Earth’s crust. Using novel techniques and equipment, the researchers studied traces of magnetism preserved in the ancient rocks, showing that some of the Earth’s earliest surface was moving at a rate of 6.1 centimeters per year and 0.55 degrees every million years.
Both the speed and direction of this latitudinal drift leaves plate tectonics as the most logical and strongest explanations for it.
In the paper, the scientists also describe what’s believed to be the oldest evidence of a complete reversal of Earth’s geomagnetic fields. This type of flip-flop is a common occurrence in Earth’s recent geologic history with the pole’s reversing 183 times in the last 83 million years and perhaps several hundred times in the past 160 million years, according to NASA.
The study argues that the planet’s magnetic field was likely stable and strong enough to keep solar winds from eroding the atmosphere already 3.2 billion years ago. This insight, combined with the results on plate tectonics, offers clues to the conditions under which the earliest forms of life developed.
“It paints this picture of an early Earth that was already really geodynamically mature,” Brenner said. “It had a lot of the same sorts of dynamic processes that result in an Earth that has essentially more stable environmental and surface conditions, making it more feasible for life to evolve and develop.”
The paper “Plate motion and a dipolar geomagnetic field at 3.25 Ga” is published in the Proceedings of the National Academy of Sciences (2022). Material provided by Harvard University.
