Structure of the Earth obducted onto the continental crust and preserved as ophiolite sequences. Many rocks now making up Earth's crust formed less than 100 million (1) years ago; however, the oldest known mineral grains are about 4.4 billion (4.4) years old, indicating that Earth has had a solid crust for at least 4.4 billion years. Earth's mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The mantle is divided into upper and lower mantle. The upper and lower mantle are separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is
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