Earth's 'not so' solid core filled with swirls of liquid iron, says study

The solid inner core of Earth may not be completely solid at all, as per a new study. Unlike what is generally believed, the core is a hodgepodge patchwork of solid and liquid which flow all the way to the centre.

The new research was carried out on the basis of faint echoes of earthquake waves which were seen bouncing back to the surface of the Earth from the depths of the planet. The research suggested that the inner core is more varied than what was previously understood.

According to the findings, the inner core, which increases about a millimetre (0.04 inch) every year when the liquid outer core solidifies, is likely to have grown faster in the earlier times in the history of the Earth.

“What's more, there may be swirls of liquid iron trapped inside the solid core,” said study senior author Keith Koper, a seismologist at the University of Utah, in a statement.

"A long time ago the inner core grew really fast. It reached an equilibrium, and then it started to grow much more slowly. Not all of the iron became solid, so some liquid iron could be trapped inside,” Koper said.

There is no process to directly access the core, so Koper and his team took into account data collected from 20 seismometers which were set up to measure earthquake waves and also monitor for nuclear weapons testing.

The team also focused on waves which were triggered by earthquakes of magnitude 5.7 or above, and are big enough to send vibrations across the inner core, as the seismometer read a faint echo.

"This signal that comes back from the inner core is really tiny. The size is about on the order of a nanometer. What we're doing is looking for a needle in a haystack. So these baby echoes and reflections are very hard to see,” Koper said.

Composition of Earth's core 'inhomogeneous'

The key finding, which was reported in the journal Nature on July 5, was that the composition of the core was "inhomogeneous," or varied. In other words, the earth's inner core did not smoothly solidify and is made up of a patchwork of different textures.

"For the first time we confirmed that this kind of inhomogeneity is everywhere inside the inner core," said Guanning Pang, a postdoctoral researcher at Cornell University, who participated in the research as a doctoral student at the University of Utah in the statement.

“Seismic waves scatter more the deeper they penetrate the core,” said Koper, indicating an increase in the amount of variability closer to the centre of the Earth. “This could be related to the changing rate of solidification of the core over time,” he added.