Plants, unlike animals, are autotrophs organisms that produce new biomass from inorganic resources (carbon dioxide and mineral nutrients), using light energy. By trapping solar energy in photosynthetic systems, they are able to synthesize organic nutrients. However, plants do require mineral nutrients, which they absorb from the soil surrounding their roots. The nutrients found in soil result in part from the gradual breakdown of the rocky material on Earth’s surface as a result of rain and, in some areas, freezing. Primarily composed of alumina and silica, rocks also contain smaller amounts of all the mineral elements needed by plants. Another source of soil nutrients is the decomposition of dead plants and animals and their waste products.