Earth's Magnetic Shield is 500 Million Years Older Than Previously Thought

Posted on August 1, 2015

Graphic showing Earth's magnetic field 4 billion years ago

Researchers have found that Earth's magnetic shield is 500 million years older than previously thought. John Tarduno, a geophysicist at the University of Rochester and his reserch team believe the Earth's magnetic field is more than four billion years old.

Tarduno says in a statement, "A strong magnetic field provides a shield for the atmosphere. This is important for the preservation of habitable conditions on Earth."

The Earth's magnetic field helps shield the planet from solar winds which could strip away the atmosphere and water. The field is generated by our planet's liquid iron core. Minerals like magnetite lock in the magnetic field record at the time the minerals cooled from a molten state. Scientists need to find magnetite in its pristine condition. If it returns to a molten state then the magnetic information within the minerals is reset and the ancient data is lost.

The data used by Tarduno's comes from the magnetic field strength fixed within magnetite found within zircon crystals collected from the Jack Hills of Western Australia. The zircons were formed over over a billion years and reside in an ancient sedimentary deposit. The zircons are very small (about 1/5 of a millimeter) which makes it a technological challenge to measure their agnetization. Tarduno's team used a SQUID magnetometer (a superconducting quantum interference device) to measure the magnetization of these tiny zircon crystals.

Tarduno says, "We know the zircons have not been moved relative to each other from the time they were deposited. As a result, if the magnetic information in the zircons had been erased and re-recorded, the magnetic directions would have all been identical."

Tarduno also says, "There has been no consensus among scientists on when plate tectonics began. Our measurements, however, support some previous geochemical measurements on ancient zircons that suggest an age of 4.4 billion years."

A research paper on the findings was published here in the journal, Science.

Image: Michael Osadciw/University of Rochester