Corals grow in layers that can record environmental changes year by year for centuries. Scientists have used these layers to study past climate and ocean conditions, but they may also hold information about Earth’s magnetic field. Today, the magnetic field is becoming more vulnerable to space weather like geomagnetic storms in some areas due to its weakening strength. However, we lack detailed records of how the magnetic field behaved in the past on human timescales. Our research explores whether corals can preserve magnetic signals. We studied a modern coral from the southwest Pacific and found it holds a stable magnetic record that matches the Earth's field where it grew. This is a promising first step toward using corals to build precise magnetic time series from the past.