Step-by-step lifecycle of a Diatom: 1. A living diatom floats in the ocean using sunlight to make food (photosynthesis). 2. It reproduces by dividing its 'soap box' cell wall. 3. The diatom eventually dies and its body sinks. 4. Its soft parts rot away, leaving only the indestructible glass-like silica wall. 5. This wall settles at the bottom of the sea. 6. Millions of these shells collect over many years to form a thick, powdery layer called Diatomaceous Earth.