A dual origin of lunar formations by both exogenous and endogenous mechanisms is now generally accepted. These processes are normally equated with impact and volcanism respectively, but many aspects of the latter cannot be readily identified with present-day terrestrial volcanism. It is proposed that lunar volcanism involved large volumes of gases and volatiles, so that ‘fluidization’ of particulate systems occurred. Terrestrial fluidization structures and model studies are described and illustrated. Certain lunar rilles and transient phenomena are also suggested to result from degassing of the interior. Some possible applications of fluidization to Mars and the synthesis of electropolymers are mentioned.

The model of the origin of the Moon in the circumterrestrial swarm during the active stage of the Earth's growth [1, 2] receives now a support (see e.g. [3]). In this model the feeding substance is the same for both bodies. However two different processes may be mentioned of chemical fractionation between the Earth and the Moon.

The Rb87-Sr87 ages of many of the lunar rocks suggest that the fundamental differentiation took place 4.5 × 109 yr ago and that remelting occurred without exchange of the rubidium and strontium with the surroundings. The Apollo A rocks are an exception to this. They appear to have acquired rubidium without all of the Sr87 produced during the first aeon. Also in the remelting about half of the radiogenic leads were lost to the surroundings probably the soil by a vaporization process. We interpret these results to mean that remelting occurred in a system that was nearly closed to the surroundings and that the high early concentrations of radioactive elements in highly insulating surroundings made this possible.

New data on the Moon obtained from its study by space probes and analyses of returned lunar samples give new ‘boundary conditions’ for a study of its origin and evolution.

Two types of tide-linked lunar phenomena now exist: the so-called lunar transient events, short-lived changes in brightness or colour and obscurations in small areas of the Moon (the reported duration is typically from a few seconds to a few hours and the areas involved are usually a few kilometres or less in diameter); and the A- and B-type seismic signals relayed back from the Apollo 12 passive seismic experiment. The frequency diagrams of both the lunar transien t events and the seismic signals show strong peaks at perigee when the Earth is closest to the Moon, with a smaller peak at apogee (transient events and B-type signal only) and both have been attributed to endogenous causes.

Both sets of data appear to be linked to areas where cracks and rilles exist. The most likely interpretation of the two sets of observations is that they are complementary and that some sort of gas release and excitation (in the cases of the glows and colour changes) is involved.

Association of the lunar events with craters with seamed and cracked floors and with other crack systems is described. Only a few associated areas of the Moon-wide lineament systems have been noted, but the Apollo 12 seismometer signals seem likely to originate from the nearby system of parallel features in the Fra Mauro area. The case for possible gas volcanism is examined.