Scientists produce new estimate of how old the Earth's core is

A view of the Earth appears over the Lunar horizon as the Apollo 11 Command Module comes into view of the Moon (NASA/Newsmakers)

Scientists have produced a new estimate of just how old the Earth's core is.

And it is relatively young, the researchers suggest, with the new study coming in at the bottom of recent estimates.

The new work saw researchers simulate the conditions at the centre of the Earth using a chamber in a laboratory, and use that experiment to improve our understanding of how old the real solid inner core might be.

It is somewhere between a billion and 1.3 billion years old, the new work suggests.

That is at the younger age of the roughly 1.3 billion years to 4.5 billion years that previous estimates have indicated. But it is much older than a recent study, which put the age at a relatively young 565 million years, concluded.

As well as improving our estimate of the age of the Earth's core, the new work helps shed new light on the processes that are taking place inside the Earth. It gives new information on how the core conducts heat, as well as a better understanding of what is powering the Earth's geodynamo, the mechanism that keeps the Earth's magnetic field in place and does everything from underpinning compasses to protecting us from harmful cosmic rays.

"People are really curious and excited about knowing about the origin of the geodynamo, the strength of the magnetic field, because they all contribute to a planet's habitability," said Jung-Fu Lin, a professor at The University of Texas at Austin's Jackson School of Geosciences who led the research.

The centre of the Earth is made up of an inner core of solid iron and an outer one of liquid iron. Researchers have attempted to look at the way the iron transfers heat to understand other information about the core, including how old that solid inner core might be.

Estimates of that conductivity have varied wildly, and so have the estimates of the age that come from it. One of the problem with the estimates that show that the world being relatively young – as in the new study – is that it seems to suggest that the core would have needed to be unrealistically hot to maintain the geodynamo, long before the inner core was formed.

To better understand those processes, researchers recreated the conditions inside the core, where the pressure is equivalent to a million atmospheres and the temperature can be nearly as hot as the Sun. They did so by heating iron with lasers and then squeezing it between two diamond anvils.

Two years of work showed that the material is as much as 50 per cent less conductive than estimates from the young core. That in turn led scientists to believe that the geodynamo was at first sustained by thermal convection, and later helped out by a process called compositional convection, with each mechanism now working together roughly equally to produce the Earth's magnetic field.

That discovery helped researchers build a picture of when the Earth would have cooled to the point that the inner core crystalised and became solid. Using their understanding of that process, the researchers were able to come to their new estimate of the core's age.

An article on the findings, 'Reconciliation of Experiments and Theory on Transport Properties of Iron and the Geodynamo', is published in Physical Review Letters.