Noosphere, according to the thought of Vladimir Vernadsky and Teilhard de Chardin, denotes the "sphere of human thought". The word is derived from the Greek (nous "mind") + (sphaira "sphere"), in lexical analogy to "atmosphere" and "biosphere".
In the original theory of Vernadsky, the noosphere is the third in a succession of phases of development of the Earth, after the geosphere (inanimate matter) and the biosphere (biological life). Just as the emergence of life fundamentally transformed the geosphere, the emergence of human cognition fundamentally transforms the biosphere. In contrast to the conceptions of the Gaia theorists, or the promoters of cyberspace, Vernadsky's noosphere emerges at the point where humankind, through the mastery of nuclear processes, begins to create resources through the transmutation of elements.