Root hairs are tiny projections and outgrowths on the outermost layer of the root epidermis. They occur near the tips of roots, where they are abundant; in particular, they increase the surface area of the root system, allowing the roots to absorb water and minerals more efficiently. Root hairs are short-lived, and new ones are produced at approximately the same rate as older ones die. They are extensive, too: In a study on one rye plant, it was estimated that the plant had approximately fourteen billion root hairs, with an absorbing surface area of 480 square yards (401 square meters). If these root hairs were placed end to end, they would extend well over 6,214 miles (10,000 kilometers)!