Giant Impact and Cataclysm: Consensus Premature

Consensus can impede understanding, and not just on the issue of climate change. The "giant impact" hypothesis commands such a consensus in the planetary sciences community relative to the origin of the Moon. The "large impact cataclysm" hypothesis involving the early history of the solar system similarly has corralled a consensus. Both are attractive hypotheses; however, until each can explain all the significant facts, the community should test each against inconvenient facts and alternative hypotheses. For example, computer models of a giant impact origin do not explain the presence of a deep, volatile-rich, chondritic reservoir within the Moon, tapped by the eruptions of orange and green pyroclastic glasses at the Apollo 17 and Apollo 15 sites, respectively. Such a reservoir is inconsistent with the extremely high temperatures to which lunar precursor materials are subjected in the giant impact models. A concerted effort to model independent accretion of the Moon, with subsequent capture by the Earth, might well provide an acceptable alternative to the giant impact hypothesis - the latter being, in essence, capture by impact. Conversely, the large impact cataclysm hypothesis stubs its toe because of an absence of Apollo and meteoritic samples of materials produced by large lunar impacts with relative ages older than Imbrium and Serenitatis. 14 relative young large basins, those with distinct mascons and probable ages around 3.85 Gyr, have apparently largely resurfaced the crust and left the statistical impression of a single cataclysm. We do not yet have formation ages on the 35+ large basins without mascons and having older relative ages than the mascon basins. Absent ages on some of these older basins, the possibility of an extended large basin formation period, possibly with episodic pulses of impactors, should be tested against both the sample collection and possible dynamical interactions in the outer solar system.