Science Focus - the home of BBC Science Focus Magazine
Earth Core © Getty

Scientists have measured how Earth’s core grows (and found something really strange)

Published: 04th June, 2021 at 17:24
Subscribe to BBC Science Focus Magazine and get 6 issues for just £9.99

A University of California discovery of an asymmetric growth at Earth’s centre is posing new questions about how the planet generated its magnetic protection.

Here's news that will shake you to your core: Earth’s solid-iron centre is growing faster on one side than the other. And experts can’t explain why.


Although scientists first expected any new growth of the planet’s inner core (caused by the cooling of the molten iron surrounding it) would happen randomly throughout the sphere, seismologists at the University of California, Berkeley have found the opposite. By studying seismic waves travelling through the Earth, the team found the core grows faster in the area under Indonesia’s Banda Sea.

While not proven, this indicates that something in Earth’s outer core under Indonesia is removing heat from the inner core at a faster rate than on its opposite side (the area under Brazil). The exact cause? Unknown.

Fortunately, all this doesn’t mean Earth has a lopsided core: the research suggests gravity equalises any asymmetric growth, pushing new iron crystals toward the north and south poles. This 'ironing' effect could maintain a spherical inner core, one that grows in radius by an average of 1mm per year.

Read more about the Earth:

Interestingly, the scientists discovered Earth’s inner core may be only 500 million years old – a fraction of Earth’s 4.5 billion years of existence. This raises big questions about how Earth formed a magnetic field (the field that protects us from dangerous particles from the Sun) without a solid inner centre. Currently, the release of heat from the inner core plays a major role in generating this field.

"We know the magnetic field already existed three billion years ago, so other processes must have driven convection in the outer core at that time," Prof Barbara Romanowicz, from the University of California, Berkeley's department of Earth and planetary science, said about the new mystery.

Dr Daniel Frost, the paper's co-author, added: "The complication is: if the inner core has been able to exist only for 1.5 billion years, based on what we know about how it loses heat and how hot it is, then where did the older magnetic field come from?"

Today, Earth's interior is made of several layers, with a solid iron-nickel inner core 1,200km in radius (about three-quarters the size of the moon) at the centre. This is covered by an outer core of molten iron and nickel about 2,400km in thickness, which is in turn surrounded by a mantle of hot rock 2,900km deep. The cool and rocky crust at the very top of the planet is a mere 5 to 70km thick.

Read more about the Earth:



Thomas Ling
Thomas LingStaff Writer, BBC Science Focus

Thomas is a Staff Writer at BBC Science Focus and looks after all things Q&A. Writing about everything from cosmology to anthropology, he specialises in the latest psychology and neuroscience discoveries. Thomas has a Masters degree (distinction) in Magazine Journalism from the University of Sheffield and has written for Men’s Health, Vice and Radio Times. He has been shortlisted as the New Digital Talent of the Year at the national magazine Professional Publishers Association (PPA) awards.


Sponsored content