New research determined when the Earth's core was formed as it "froze" away from the molten iron outer core billions of years ago.

Earth's inner core consists of a ball of solid iron surrounded by a liquid outer core, the University of Liverpool reported. This core is believed to be a relatively new addition to the planet, and to determine when it formed a team of researchers analyzed magnetic records from ancient igneous rocks. The findings showed there was a dramatic increase in the Earth's magnetic field between one billion and 1.5 billion years ago, indicating this is when the core first appeared.

"This finding could change our understanding of the Earth's interior and its history," Liverpool palaeomagnetism expert and the study's lead author, Andy Biggin said. "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 findings suggests the Earth's core is cooling more slowly than was previously believed and the average growth rate of the solid inner core is about 1 millimeter per year. These findings could influence our understanding of the Earth's magnetic field, and Earth sciences as a whole.

The Earth's magnetic field is created by the motion of the liquid iron alloy in the outer core, which occurs as a result of convection from the core losing heat to the overlying solid mantle that extends up to the crust. Once the inner core begins to freeze, the convection receives a boost in power from the non-metallic elements that remain molten in the outer core. This process still exists today, and is believed to be one of the primary drivers of Earth's magnetic field.

"The theoretical model which best fits our data indicates that the core is losing heat more slowly than at any point in the last 4.5 billion years and that this flow of energy should keep the Earth's magnetic field going for another billion years or more," Biggin said. "This contrasts sharply with Mars which had a strong magnetic field early in its history which then appears to have died after half a billion years."

The findings were published in a recent edition of the journal Nature.