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
What Is the Third Estate? What Is the Third Estate? What Is the Third Estate? () is a political pamphlet written in January 1789, shortly before the outbreak of the French Revolution, by the French thinker and clergyman Abbé Emmanuel Joseph Sieyès (1748–1836). The pamphlet was Sieyès' response to finance minister Jacques Necker's invitation for writers to state how they thought the Estates-General should be organized. In the pamphlet, Sieyès argues that the third estate – the common people of France – constituted a complete nation within itself and had no need of the "dead weight" of the two other orders, the first and second