Precursors are substances or elements that exist before a particular event or process occurs. In chemistry, they are often the initial materials that undergo transformation to create a final product. For example, in the production of pharmaceuticals, specific precursors are required to synthesize active ingredients. In a broader context, precursors can refer to anything that precedes and signals the onset of something else. For instance, certain environmental changes can be precursors to natural disasters like earthquakes or floods. Recognizing these precursors can help in predicting and mitigating potential risks.