It has been widely believed that Earth's magnetic shield has been intact for 3.45 billion years, but new research suggests it's much older than we thought.
A recent study uncovered evidence that the magnetism protecting our planet from solar winds is actually four billion years old, the University of Rochester reported.
Earth's magnetic field is generated by its iron core, which requires regular heat from the plant in order to operate, and this heat is helped to the surface by plate tectonics. The time of origin of plate tectonics has been widely debated, and determining the age of the magnetic shield could help solve the mystery. Minerals such as magnetite could help answer some of these questions because they lock in the magnetic field record at the time they cool from a molten state.
To gain insight into the age of the magnetic shield, a research team looked at zircon crystals collected from the Jack Hills of Western Australia. They used a unique superconducting quantum interference device (SQUID magnetometer) that allowed them to analyze the minerals with extremely high sensitivity. In order to make sure their readings were valid, the researchers had to make sure the magnetite within the zircon had not been exposed to damaging levels of heat. About 2.6 billion years ago the Jack Hills reached extremely high temperature, which could have erased the minerals' magnetic records and replaced them with new ones.
"We know the zircons have not been moved relative to each other from the time they were deposited," said John Tarduno, a geophysicist at the University of Rochester and a leading expert on Earth's magnetic field. "As a result, if the magnetic information in the zircons had been erased and re-recorded, the magnetic directions would have all been identical."
Despite these worrisome factors, the scientists determined the minerals revealed varying magnetic directions, suggesting the intensity measurements recorded in the sample were over four billion years old after all.
"There has been no consensus among scientists on when plate tectonics began," Tarduno said. "Our measurements, however, support some previous geochemical measurements on ancient zircons that suggest an age of 4.4 billion years."
During this time the magnetic field would have been especially important because solar winds were about 100 times stronger than they are today. If the magnetic shield had not existed, the protons in invading solar winds would have ionized and stripped light elements from the atmosphere, drying up all the water on Earth.
Scientists believe Mars also had a dynamic core dynamo (magnetic core iron) when it was formed, but this only lasted for about four billion years. This could explain why the Red Planet has no detectable magnetic field and extremely thin atmosphere today.
"It may also be a major reason why Mars was unable to sustain life," Tarduno concluded.
The findings were published in a recent edition of the journal Science.
