Magnesium-oxide minerals “snow” out of the core.
Earth’s magnetic field (or geodynamo) is a mystery — it is believed by some that it is generated by the radioactive decay of Earth’s core, resulting in mixing in Earth’s outer core. However, nobody has ever been able journey to the center of the Earth to find out for certain. Now, a new theory has been proposed to explain the mechanism behind its generation.
A pair of planetary scientists, Joseph O’Rourke and David Stevenson from the California Institute of Technology, recently published a paper in the journal Nature suggesting that magnesium may be the source of Earth’s magnetic field.
Previously, scientists believed that Earth’s magnetic field was generated by energy that is released as the core cools and solidifies through radioactive decay, which causes mixing in the liquid-metal outer core. However, the problem with this theory is that the core did not cool enough to form an inner core until approximately one billion years ago. There had to be something else generating the magnetic field before this time.
Magnesium is the fourth most common element in Earth’s outermost layers, however scientists thought there was almost no magnesium in the core because iron and magnesium do not mix very well.
Magnesium likely made its way to the core of the planet early in its formation through collisions with protoplanets roughly 3.4 to 4.2 billion years ago. Due to these violent collisions, temperatures and pressures were so powerful that iron and magnesium formed an alloy. Magnesium could make up as much as one percent (by weight) of the material in the core.
O’Rourke, a graduate student and study lead author, along with Stevenson, a Caltech professor, created a model of Earth’s formation to study how magnesium behaves in the core. As Earth’s core cooled, magnesium-oxide minerals precipitated or “snowed” out from the core. Since this magnesium is lighter than liquid metal, it floated outward through the outer core, both mixing it and powering the convection that produces the magnetic field.
This theory could explain how the magnetic field has been around for so long and still exists today. “We think we now understand why the Earth has had a magnetic field for the last 4 billion years, and that the process will keep happening into the foreseeable future,” said O’Rourke to Discovery News.
So far the team has only used computer models to develop this theory, so experimental tests have to be performed to provide evidence.
Luckily, one group is already conducting these types of experiments. James Badro, a geophysicist at the Institut de Physique du Globe in Paris, recently completed simulations that agree with O’Rourke and Stevenson’s modeling.
The magnetic field is important for life on Earth since it protects us from the sun’s deadly solarwinds. We definitely want to understand how it formed, not only to improve our understanding of this mystifying planet we call home, but also to make sure the magnetic field will stay around for awhile.