Ancient Rocks Unlock Mystery of When Earth's Core Formed Scientific estimates have long differed on when inner core formed.

 -- Earth is a magnificent, mysterious place that continues to surprise scientists.

Scientists have long disagreed on when Earth's solid iron inner core was formed, but a new study has zeroed in on its approximate age thanks to clues left in the magnetic signature of ancient igneous rocks.

While previous estimates have put the inner core at 500 million to 2 billion years old, a new study from an international team of scientists published in the journal "Nature" has found the Earth's interior is somewhere around one to 1.5 billion years old.

Scientists made the determination by examining igneous rocks and determining there was an increase in Earth's magnetic field between one to 1.5 billion years, corresponding with the time they believe the inner core began to freeze due to cooling from the molten outer core.

"This finding could change our understanding of the Earth’s interior and its history," Andy Biggin, the lead author of the study who works at the University of Liverpool's School of Environmental Sciences, said in a statement.

"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," he said. "It also suggests an average growth rate of the solid inner core of approximately 1 millimeter per year which affects our understanding of the Earth’s magnetic field."

Scientists were also able to create a model with their data, showing that the flow of energy from Earth's inner core should keep our planet's magnetic field strong for at lease another one billion years or more.

"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," Biggin said.