Age of the Earth research. Most geological samples from Earth are unable to give a direct date of the formation of Earth from the solar nebula because Earth has undergone differentiation into the core, mantle, and crust, and this has then undergone a long history of mixing and unmixing of these sample reservoirs by plate tectonics, weathering and hydrothermal circulation. All of these processes may adversely affect isotopic dating mechanisms because the sample cannot always be assumed to have remained as a closed system, by which it is meant that either the parent or daughter nuclide (a species of atom characterised by the number
ITS launch vehicle "evolved quite a bit" since the November 2016 articulation of the very large "ITS launch vehicle." A key driver of the new architecture is to make the new system useful for substantial Earth-orbit and cislunar launches so that the new system might pay for itself, in part, through commercial spaceflight activities in the near-Earth space zone. In September 2017, the new smaller design was revealed to be the diameter launch vehicle, referred to by its "code name" BFR, with similar core vehicle structure (carbon fiber), engines (Raptor), and Mars mission architecture; but explicitly aimed at superseding and replacing the entire