Earthen buildings come in a vast variety of shapes and sizes, made from materials like fired clay, compressed dirt and a mixture of clay, sand, straw and water. People have been using various forms of earth to build structures for centuries. Iranian architecture displays great variety, both structural and aesthetic, developing gradually and coherently out of earlier traditions and experience. Currently it is estimated that one half of the world's population approximately three billion people on six continents lives or works in buildings constructed of earth and while the vast legacy of traditional and vernacular earthen construction has been widely discussed, little attention has been paid to the contemporary tradition of earth architecture. It is a renewable building material that is simply borrowed from the earth for the life of the building and can be recycled indefinitely as a building material or returned to the earth. The thermal mass of the earth used in construction can be used to store both warmth and coolness, thus balancing diurnal fluctuations in temperature throughout the year.