In Haggerty’s model, carbonado arrived as a meteorite, possibly during the Late Heavy Bombardment between about 3.8 and 4.2 billion years ago, when the inner solar system was struck by unusually many impactors[1]. The oldest age measured on carbonado, about 3.8 billion years, falls within that window[1].
Haggerty has also said in interviews that he favors a single asteroid, with the stones arriving embedded in another rock that later weathered away[2,3]. His review adds a geographic argument: carbonado was “undoubtedly widespread during the bombardment,” but most falls landed in the oceans of the time, leaving preserved remnants only on the block of crust later split between Brazil and the Central African Republic[1].
He points to analogues. Asteroid 2008 TC3 was tracked entering the atmosphere and fell in northern Sudan as a diamond-bearing ureilite whose diamonds reach about 100 micrometers, unusually large for that class[1]. Sub-micrometer diamond has been reported in Libyan desert glass, which some researchers attribute to a cometary airburst[1].
The objections are substantial. Diamonds known from impact sites—in Arizona, the Ries in Germany and Popigai in Russia—are discrete microdiamonds, not carbonado[1]. The Bangui magnetic anomaly in the Central African Republic, once thought to mark a buried iron meteorite, was later shown to be a banded iron ore body of crustal origin[1].
Haggerty also lists independent lines of evidence that he regards as lending credence to the model: synthetic diamond-like glass produced in experiments, nanodiamond encased in glassy carbon shells in the interstellar medium, glassy carbon and nanodiamond produced experimentally and in supernova shock waves, and the finding that Mercury has a crust of graphite, now buried by volcanic rock but exposed in impact craters[1]. Each of these shows that unusual carbon can form in space; none shows that carbonado did.
The arrival chapter is therefore the most conjectural part of the story. It is internally consistent with the age data, but its decisive evidence—a dark, porous, patinaed diamond observed to fall, or identified among the asteroids—has not been reported[1].