Soil forms slowly through the weathering of bedrock and accumulation of organic matter over long time scales. The rate of soil formation is determined by climate, organisms, parent material, topography, and time. Soil formation balances against the downward migration and potential erosion of soil horizons. Over hundreds or thousands of years, distinct soil horizons like the A, B, and C horizons may develop. However, at rates of modern soil loss due to agriculture, the entire 1 meter thickness of topsoil could erode away within 1000 years, shorter than the lifespan of many civilizations. Once lost, soils take a very long time to recover.