Solid Metal Ball Rotates Independently Inside Earth
Deep within Earth lies a solid metal ball, rotating independently from the planet itself. This inner core, first discovered by Danish seismologist Inge Lehmann in 1936, has long fascinated scientists. Recent studies suggest dramatic changes in its rotation, sparking debate over its speed and direction.
Seismic waves offer clues
Direct observation of Earth’s core is impossible, but seismologists study the inner core’s motion by examining how seismic waves from large earthquakes behave. These waves provide insights into changes in the core’s position and rotation.
“Differential rotation of the inner core was proposed as a phenomenon in the 1970s and ’80s, but it wasn’t until the ‘90s that seismological evidence was published,” said Dr. Lauren Waszek, a senior lecturer at James Cook University.
New evidence supports changing rotation
In 2023, a model suggested that the inner core, once spinning faster than Earth, is now slowing down and may even be moving in reverse. A new study published in Nature on June 12 confirms this slowdown and supports the idea that the core’s rotation follows a 70-year cycle.
“We’ve been arguing about this for 20 years, and I think this nails it,” said Dr. John Vidale, coauthor and Professor of Earth Sciences at the University of Southern California.
Implications and future research
Despite the new findings, some scientists remain unconvinced about the core’s behavior and its impact on Earth, particularly its magnetic field. The inner core, made mostly of iron and nickel, is surrounded by a liquid metal outer core. This interaction generates electrical currents powering Earth’s magnetic field.
As seismic waves from earthquakes and nuclear tests pass through the inner core, they reveal changes in its rotation. Vidale and his team observed 121 such instances from 1991 to 2023, confirming the 70-year rotation cycle.
Impact on Earth’s magnetic field
The interaction between the inner and outer cores affects Earth’s magnetic field, which shields the planet from solar radiation. Although the exact influence of the inner core on the magnetic field is unknown, a slower-spinning core could potentially shorten the length of a day by mere thousandths of a second.
Researchers remain divided on whether the inner core’s rotation has been fully understood. “We need more data and improved interdisciplinary tools to investigate this further,” said Waszek. Understanding the inner core’s behavior is crucial for learning how Earth’s deep interior formed and how it connects with the planet’s other layers.
Exciting potential
The boundary where the liquid outer core meets the solid inner core is particularly intriguing. Vidale speculates about potential volcanic activity at this boundary, where solid and fluid interact.
“We might have volcanoes on the inner core boundary, for example, where solid and fluid are meeting and moving,” he said.
As scientists continue to study the inner core, new methodologies will be essential in answering lingering questions about its rotation and overall structure. The inner core remains a profound mystery, with each discovery adding to our understanding of Earth’s complex interior.