Earth’s magnetic field is now thought to be at least four billion years old. As this magnetic field is crucial to protecting the Earth’s atmosphere, pinpointing when the magnetic field first arose could help us uncover how long our planet has been habitable.

The magnetic field allows life on our planet because it prevents solar winds from eroding away Earth’s biology-sustaining atmosphere and oceans. This feature is formed by a rotating liquid iron core at the heart of Earth known as geodynamo. In order for this geodynamo to operate, it needs heat from the planet. Plate tectonics are thought to help with this vital heat release, transferring it from the Earth’s interior to its surface.

John Tarduno, a geophysicist at the University of Rochester, first estimated that the Earth's magnetic field was 3.45 billion years old. But new data from ancient rock crystals suggests they were about half a billion years off. Tarduno and his research team collected zircon crystals from the Jack Hills of Western Australia, and by sampling crystals of different age, they were able to determine the history of the magnetic field.

These crystals contain minerals called magnetite, which preserve a record of the Earth’s magnetic field from the moment they first cool from their molten state. Researchers used a superconducting quantum interference device (SQUID) to measure the weak signal and detect the magnetic fields.

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

Researchers found that the minerals had varying magnetic directions, which suggests they had not been remagnetized during their history. They took this as confirmation that the magnetic intensity measurements recorded from the rock samples were in fact four billion years old. Furthermore, the values were sufficiently high to indicate the presence of a geodynamo at this time. The findings, published in the journal Science, suggest that Earth had a magnetic field and plate tectonics in its infancy – a hotly debated topic.

According to Tarduno, these findings could provide another answer as to why Mars was unable to sustain human life. While Earth was able maintain its magnetic field, the Red Planet lost its geodynamo early on.

"So part of the reason that Mars lost its atmosphere is not simply that it has less gravity, but also that it didn't have a magnetic field protecting the atmosphere from being blown away," Tarduno told ABC.

Tarduno does admit that the science community is yet to reach a consensus about when plate tectonics began, but suggests his measurements “support some previous geochemical measurements on ancient zircons that suggest an age of 4.4 billion years.”

But, as Science Magazine’s Eric Hand explained, some scientists are more skeptical. Ben Weiss, a researcher from the Massachusetts Institute of Technology, and his research team were unable to replicate Tarduno’s results. Tarduno defended his study against Hand’s conclusion, saying “they haven’t even measured the magnetization that we have.”