Scientists Say Earth's Inner Core Formed 1 to 1.5 Billion Years Ago

Posted on October 8, 2015

Diagram of Earth's inner core

Scientists say Earth's inner core formed 1 to 1.5 billion years ago. The scientists say the core "froze" from the surrounding molten iron outer core. Previous estimates of the inner core formation have ranged from .5 billion to 2 billion years ago.

The researchers analyzed magnetic records from ancient igneous rocks. They found there was a sharp increase in the strength of the Earth's magnetic field between 1 and 1.5 billion years ago. A related study from earlier this year found Earth's magnetic field is over four billion years old. When the inner core began to freeze the convection generated by the motion of the liquid iron alloy in the outer core increased.

Dr. Andy Bigger, University of Liverpool palaeomagnetism expert and lead author of the study, says in a statement, "This finding could change our understanding of the Earth's interior and its history. 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."

Dr. Biggin also says the finding "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."

Dr. Biggins also says the theoretical model that best fits with their findings indicates the core is losing heat more slowly than at any point in time over the past 4.5 billion years. He says the flow of energy should keep Earth's magnetic field going for at least another billion years.

Biggins says, "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 new study was published here in the journal, Nature. It also included scientists from Helsinki, Michigan Tech, UC San Diego, and the Chinese Academy of Sciences.

Image: Kay Lancaster, Department of Earth, Ocean and Ecological Sciences