'70-year cycle': Earth's inner core is now moving in reverse Produced by: Tarun Mishra Significant Discovery  on Earth's Core Recent research has confirmed that Earth's inner core, a solid metal ball, has slowed dramatically and is now rotating in reverse compared to its previous direction. Historical Context Discovered by Danish seismologist Inge Lehmann in 1936, the inner core has intrigued researchers for decades. Its rotation speed and direction have been hotly debated. Challenges in Observation Direct observation of Earth's deep interior is impossible, making it challenging to study. Seismologists rely on waves from large earthquakes to infer details about the core's motion. Evidence from Seismology Seismologists have measured changes in the inner core’s position and spin by comparing waves from similar earthquakes that passed through the core at different times, as reported by CNN. Debate on Core Rotation Proposed in the 1970s and supported by evidence in the 1990s, the inner core's differential rotation has been a contentious topic. Researchers have disagreed on the rate and direction of its spin relative to the mantle. New Model and Findings A 2023 model suggested that the inner core, once spinning faster than Earth, had slowed and eventually reversed direction. Recent research published in Nature on June 12 supports this hypothesis and indicates the core's spin follows a 70-year cycle. Implications and Observations Dr. John Vidale and his team observed seismic waves from earthquakes and Soviet nuclear tests to track the core’s changes. The findings reveal the core's variable spin rates, which could influence Earth's magnetic field and shorten the length of a day. Ongoing Questions Despite the advancements, uncertainties remain due to the core's inaccessibility. Further research is needed to understand the full implications of the inner core's behaviour on Earth's geodynamics and magnetic field. Related Stories