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.
Igneous rocks are formed from the solidification of molten rock material. There are two basic types. Intrusive igneous rocks crystallize below Earth's surface and the slow cooling that occurs there allows large crystals to form. Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite. Extrusive igneous rocks erupt onto the surface where they cool quickly to form small crystals. Some cool so quickly that they form an amorphous glass.