So we expect that the description of the velocities of molecules in a gas will in fact be the most probable distribution, since we are dealing with particle numbers in the range of Avogadro's number. But this most probable distribution (the Maxwell-Boltzmann distribution) is subject to constraints, namely that the number of particles is constant and that the total energy is constant (conservation of energy).
The oldest rocks are metamorphic gneisses which are to be found on Inishtrahull, several miles off Malin Head in Co. Donegal, and elsewhere in the north-west. They originally formed as igneous rocks 1750-1780 million years ago.
Underground, they are formed when magma deep within the Earth becomes trapped in small pockets. As these pockets of magma cool slowly they become igneous rocks. Igneous rocks are also formed when volcanoes erupt. Igneous rocks are formed as the lava cools above ground.The upper 16 km of the Earthâs crust is composed of 95% igneous rock. Intrusive igneous rocks are formed from magma that cools and solidifies underground.These rocks are coarse grained.xtrusive igneous rocks are formed at the crustâs surface as a result of the partial melting of rocks within the mantle and crust. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks and are fine grained.