Extinction [Nickeliferous magnetites]
Discussions by Yann Oliver
Up: Extinction [Proofs for an extraterrestrial impact]
In the K-T sediments, some little clay spheres have been found. They contain unusual quantities of nickel and trivalent iron.
Analogous structures in the earth contain very little nickel (which is very rare in the earth crust), and less oxidised iron. Analogous structures in meteorites contain no nickel (which is present in the meteorite but not in the spheres), and no trivalent iron.
However, during the fall of a meteorite through the atmosphere, the iron becomes oxidised (due to the atmospheric oxygen) and (due to fusion), in small meteorites and at the surface of big ones, spheres with the same composition as those of the K-T limit are formed.
Thus, these structures are the trace of the fall of a meteorite through the atmosphere.
An interesting point is that the finds at different places differ slightly in chemical composition (chromium, aluminium...). This could mean that the K-T meteorite broke in several pieces before the collision.