Tracking cell activity is essential for understanding biological processes. An ultimate aspiration in biology is to map the dynamics of all cells of interest within an intact organ or organism in space and time, a goal yet to be achieved. In my career, I am committed to fulfilling this ambition through a new sensing modality that records the activity history in individual cells for endpoint readout, resembling tree rings that document climate history. By leveraging in cellulo protein assemblies as molecular memory, we will develop intracellular recording platforms that are genetically encodable, orthogonal to cell processes, generalizable for mapping diverse cellular events, and applicable for in vivo recording. We will create computational methods to retrieve recorded signals at high throughput, generating spatiotemporal maps of cell dynamics throughout the entire organ. This paradigm shift will allow us to reveal development, aging, pathogenesis, and beyond in unprecedented detail.