Billions of years ago, Earth’s magnetic field may have gotten a jump-start from a turbulent magma ocean swirling around the planet’s core.
Our planet has generated its own magnetism for almost its entire history (SN: 1/28/19). But it’s never been clear how Earth created this magnetic field during the planet’s Archean Eon — an early geologic period roughly 2.5 billion to 4 billion years ago. Now, computer simulations suggest that a deep layer of molten rock-forming minerals known as silicates might have been the culprit.
“There’s a few billion years of Earth’s history where it’s difficult to explain what was driving the magnetic field,” says Joseph O’Rourke, a planetary scientist at Arizona State University in Tempe who was not involved with this study. This new result, he says, is a “vital piece of the puzzle.”
Today, Earth’s magnetism is likely generated in the planet’s outer core, a layer of liquid iron and nickel. Heat escaping from the solid inner core drives flows of fluid that create circulating electric currents in the outer core, turning Earth’s innards into a gigantic electromagnet. The outer core, however, is a fairly recent addition, appearing roughly a billion or so years ago, and ancient rocks preserve evidence of a planetwide magnetic field much earlier than that. So, some other mechanism must have been at work during Earth’s formative years.
