Earth's inner core was formed 1-1.5 billion years ago as it 'froze' from the surrounding molten iron outer core, according to a new study. The inner core is Earth's deepest layer and a relatively recent addition to our planet. Establishing when it was formed is a topic of vigorous scientific debate with estimates ranging from 0.5 billion to 2 billion years ago.
Researchers from the University of Liverpool, UK, and colleagues analysed magnetic records from ancient igneous rocks.The timing of the first appearance of solid iron or "nucleation" of the inner core is highly controversial but is crucial for determining the properties and history of the Earth's interior and has strong implications for how the Earth's magnetic field - which acts as a shield against harmful radiation from the Sun, as well as a useful navigational aid - is generated. "The results suggest that the Earth's core is cooling down less quickly than previously thought which has implications for the whole of earth sciences.
"It also suggests an average growth rate of the solid inner core of approximately 1mm per year which affects our understanding of the Earth's magnetic field," said Biggin.
The Earth's magnetic field is generated by the motion of the liquid iron alloy in the outer core, approximately 3,000 km beneath the Earth's crust.
These motions occur because the core is losing heat to the overlying solid mantle that extends up to the crust on which we live producing the phenomenon of convection.Once the inner core started to freeze, this convection received a strong boost in power because light, non-metallic elements remained molten in the outer core and were buoyant relative to the overlying liquid. The process continues today and is thought to be the main source of "fuel" for generating the Earth's magnetic field.