Lithosphere for silicate rocks, and formula_4 is the age of the given part of the lithosphere. The age is often equal to L/V, where L is the distance from the spreading centre of mid-oceanic ridge, and V is velocity of the lithospheric plate. Oceanic lithosphere is less dense than asthenosphere for a few tens of millions of years but after this becomes increasingly denser than asthenosphere. This is because the chemically differentiated oceanic crust is lighter than asthenosphere, but thermal contraction of the mantle lithosphere makes it more dense than the asthenosphere. The gravitational instability of mature oceanic lithosphere has the
Names for the human species "Gaian") is frequently used, as it were naming humanity by its planet of origin. Incidentally, this situation parallels the naming motive of ancient terms for humanity, including "human" ("homo", "humanus") itself, derived from a word for "earth" to contrast humans as earth-bound with celestial beings (i.e. deities) in mythology. Names for the human species The common name of the human species in English is historically "man" (from Germanic), often replaced by the Latinate "human" (since the 16th century). In addition to the generally accepted taxonomic name "Homo sapiens" (Latin: "sapient man", Linnaeus 1758), other Latin-based names for the human species