Geophysicists at the University of Rochester announce in todays issue of Nature that the Earths magnetic field was nearly as strong 3.2 billion years ago as it is today.
The findings, which are contrary to previous studies, suggest that even in its earliest stages the Earth was already well protected from the solar wind, which can strip away a planets atmosphere and bathe its surface in lethal radiation.
The intensity of the ancient magnetic field was very similar to todays intensity, says John Tarduno, professor of geophysics in the Department of Earth and Environmental Sciences at the University of Rochester. These values suggest the field was surprisingly strong and robust. Its interesting because it could mean the Earth already had a solid iron inner core 3.2 billion years ago, which is at the very limit of what theoretical models of the Earths formation could predict.
Geophysicists point to Mars as an example of a planet that likely lost its magnetosphere early in its history, letting the bombardment of radiation from the sun slowly erode its early atmosphere. Theories of Earths field say its generated by the convection of our liquid iron core, but scientists have always been curious to know when Earths solid inner core formed because this process provides an important energy source to power the magnetic field. Scientists are also interested in when Earths protective magnetic cocoon formed. But uncovering the intensity of a field 3.2 billion years in the past has proven daunting, and until Tardunos research, the only data scientists could tease from the rocks suggested the field was perhaps only a tenth as strong as todays.
Tarduno had previously shown that as far back as 2.5 billion years ago, the field was just as intense as it is today, but pushing back another 700 million years in time meant he had to find a way to overcome some special challenges.