Earth's magnetic shield much older than previously thought

The Earth's magnetic field is at least four billion years old, up from the previous estimates of 3.45 billion years, researchers from University of Rochester have found.

Earth's magnetic field protects the atmosphere from solar winds - streams of charged particles shooting from the Sun.

The magnetic field helps prevent the solar winds from stripping away the atmosphere and water, which make life on the planet possible.

Given the importance of the magnetic field, scientists have been trying to determine when it first arose, which could, in turn, provide clues as to when plate tectonics got started and how the planet was able to remain habitable.

"A strong magnetic field provides a shield for the atmosphere," said John Tarduno, geophysicist at University of Rochester and a leading expert on Earth's magnetic field.

"This is important for the preservation of habitable conditions on Earth," he added.

Earth's magnetic field is generated in its liquid iron core and this "geodynamo" requires a regular release of heat from the planet to operate.

Today, that heat release is aided by plate tectonics, which efficiently transfers heat from the deep interior of the planet to the surface.

But, according to Tarduno, the time of origin of plate tectonics is hotly debated, with some scientists arguing that Earth lacked a magnetic field during its youth.

The new results, published in the journal Science, are based on the record of magnetic field strength fixed within magnetite found within zircon crystals collected from the Jack Hills of Western Australia.

The zircons were formed over more than a billion years and have come to rest in an ancient sedimentary deposit.

By sampling zircons of different age, the history of the magnetic field can be determined.

Scientists believe that Mars had an active geodynamo when that planet was formed, but that it died off after four billion years.

As a result, Tarduno says, the Red Planet had no magnetic field to protect the atmosphere, which may explain why its atmosphere is so thin.

"It may also be a major reason why Mars was unable to sustain life," he concluded.