A new study published in Nature suggests that the inner core of the Earth may have solidified between 1 and 1.5 billion years ago. Previous studies have suggested that the inner core began to solidify between 0.5 and 2 billion years ago.
The inner core of the Earth is comprised of solid iron, while the outer core is liquid based. This study suggests that the solidification of the inner core boosted convection currents in the outer core. This convection in the outer core maintains the magnetic field of the Earth.
The study looked at the magnetic orientation of Precambrian aged igneous rocks and concluded that there was a sharp increase in the Earth's magnetic field 1-1.5 billion years ago. This method served as a proxy to determine when the inner core began to solidify.
The authors also suggest that the inner core is is growing at a rate of about 1 mm per year. They feel that the core of the Earth can sustain a magnetic field for at least another billion years.