Earth’s Solid Inner Core Is Surprisingly Soft Like Butter, Study Suggests

Scientists have long believed Earth’s inner core is like a huge solid metal ball.

Scientists recently discovered that Earth’s inner core, which was long thought to be hard like a solid metal sphere, might be a lot softer – more like butter. A new study, led by the University of Texas at Austin and collaborators in China, suggests that this surprising softness may be caused by hyperactive atoms that move around within their molecular structure much more than we realised. Scientists believe that this finding could now help explain some of our planet’s long-standing mysteries, like why Earth’s magnetic field constantly defies expectations. 

It is impossible to directly sample the Earth’s inner core because of its extremely high temperatures and pressures. So scientists re-created the intense pressure within the inner core in the lab and observed how the iron atoms behaved under these conditions. They then fed this data into a computer-learning program to create a simulated virtual core that they dubbed the “supercell”. Using the supercell, the researchers were then able to see how the iron atoms moved within their supposedly rigid structure. 

The results suggested that the atoms inside the inner core can “move much more than we ever imagined,” study co-author Jung Fu-Lin said. The researchers explained that the supercell simulations show that some of these atoms can move around in groups – like guests moving around a dinner table, per the press release. This type of movement is known as “collective motion”. 

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“This increased movement makes the inner core less rigid [and] weaker against shear forces,” Mr Lin said. This could explain why the inner core is “surprisingly soft,” he added.

Separately, co-lead author Youjun Zhang, who is a professor at Sichuan University, explained that this atomic movement could explain why seismic measurement of the inner core shows an environment that’s much softer and malleable than would be expected at such pressures. 

“Seismologists have found that the centre of the Earth, called the inner core, is surprisingly soft, kind of like how butter is soft in your kitchen,” he said. 

“The big discovery that we’ve found is that solid iron becomes surprisingly soft deep inside the Earth because its atoms can move much more than we ever imagined. This increased movement makes the inner core less rigid, weaker against shear forces,” Mr Zhang added. 

The researchers believe that the new findings could reveal new insights into other inner core mysteries, like how it helps to generate Earth’s magnetic field. “Now, we know about the fundamental mechanism that will help us with understanding the dynamic processes and evolution of the Earth’s inner core,” Mr Lin said.