Objectives We use a cellular automaton model to simulate the thickness of the saturated fluid layer and the roughness of the core mantle boundary (CMB), aiming to provide small-scale information for studying the undulations of the CMB.

Methods The dynamic process of model evolution is abstracted as a set of stationary stochastic processes without memory based on the physical properties of the CMB. In the two-dimensional grid of the model, the cell size is consistent with the mantle particles and is in one of three states: Mantle solid, saturated core fluid with light elements, and unsaturated core fluid with light elements. The transition of different cellular states is controlled by rate parameters that characterize the physical processes of dissolution, crystallization, and diffusion at the nuclear mantle boundary.

Results After the model evolved to a steady state, small-scale topographic changes occurred at the size of the cell units at the core mantle boundary, with a saturated fluid layer several tens of centimeters thick appearing at the boundary between the core and mantle boundaries.

Conclusions Research has shown that as the difference between the mass fraction of saturated light elements in the liquid outer core and the actual mass fraction of light elements increases, the dynamic processes of dissolution and crystallization become faster, and the thickness of the saturated fluid boundary layer gradually increases, with more pronounced oscillations over time. The roughness of the upper and lower boundaries also has similar characteristics. As the difference between the mass fraction of saturated light elements in the liquid outer core and the actual mass fraction of light elements increases, the roughness of the upper and lower boundaries increases and oscillates more significantly over time. Conversely, when the two are closer, the roughness of the upper and lower boundaries has a smaller and more stable value. The experimental results are consistent with the simulation calculation results of relevant scholars, which provide new experimental ideas for studying small-scale information of the core-mantle boundary and simulating its dynamic evolution process.