Liquid iron vortexes may be trapped in Earth's 'solid' core

The solid inner core of the Earth may not be solid in spite of everything – at least not from scratch. Instead, it's a fuzzy-shaped, solid-liquid sponge that stretches to the center.

Liquid iron vortexes may be trapped in Earth's 'solid' core

New research, based on the weak angles of earthquake waves returning from the planet's depths to the Earth's surface, shows that the inner core is more diverse than previously estimated. The findings suggest that as the liquid outer nucleus solidifies, the inner nucleus, which grows about a millimeter (0.04 in) each year, may have grown faster in earlier periods of Earth's history. Keith Koper, senior author of the study, a seismologist at the University of Utah, said there could be liquid iron entrances stuck inside the solid core.

"The inner nucleus really grew very fast a long time ago," Koper said. "It reached a balance and then began to grow much slower. Not all of the iron has solidified, so some liquid iron may be trapped inside.

The inner core of the Earth is mostly a solid cluster of iron and nickel. Approximately 1.520 miles (2.440 kilometers) long, this inner core revolves within the outer core, an ocean of melted iron and nickel, about 1,400 miles (2.260 km) thick. The metal cluster at the center of the Earth forms the planet's magnetic field. The outer nucleus has gradually crystallized over time, but scientists know little about how fast this process takes place, which raises questions about the state of the Earth's magnetic field in time.

Since there was no direct access to the nucleus, Koper and his team used data from 20 seismometers installed to measure earthquake waves and monitor nuclear weapons tests. They focused on the waves triggered by earthquakes of magnitude 5.7 or greater, which were big enough to vibrate towards the inner core and send a weak anchor to the seismometer. There were 2,455 such earthquakes in the data set.

"This signal coming back from the inner core is really very small," Koper said. "Their size is about a nanometer scale. What we're doing is something like looking for a needle in a liquid. So it's hard to see the baby's wings and reflections.

The most important finding, published in the journal Nature on July 5th, was that the nucleus' composition showed "no homogeneity" or diversity. In other words, the inner nucleus is made up of a patchwork of different tissues that is not properly solidified.

"For the first time, we have confirmed that such a homogeneity is everywhere in the inner core," said Guanning Pang, a post-doctoral researcher at Cornell University and a doctoral student at the University of Utah.

Koper said that the more seismic waves penetrate the nucleus, the more they disperse, and this indicates an increasing amount of volatility as they approach the center of the Earth. Koper added that this may be related to the core's rate of solidification, which varies over time.