Phosphorus is a very widespread element on Earth, but it does not exist in its pure state in the atmosphere. On the other hand, it is naturally present in the form of phosphates in the parent rock. Erosion causes dissolved phosphates to enter the soil, where they can be absorbed by plants. The plants combine the phosphorus with various components to make living matter that is transmitted to herbivores and then carnivores by the food chain. Animal dung and dead organisms are decomposed by micro-organisms. This process returns the phosphorus to the soil, where it can once again be assimilated by other plants.