However, one whole chapter of "Rare Earth" was devoted to plate tectonics with barely more than lip service to lunar influences, except for sea tides. There's a decade-old hypothesis to which I unashamedly lay independent claim, in that the Moon is the prime mover for tectonic plate activity. ["Moon Over Miasma," "R&D Magazine," March 1990, p. 45] And, by inference, conflicting with that standard radionuclide heating, although such radiodecay thermodynamics may play a somewhat minor role.
For starters, neither Venus nor Mars shows evidence of tectonic plate motion, nor does either have a satellite comparable to ours. Secondly, in the earlier geological eras, the Moon, being then far closer to the Earth, caused both land and sea tides of immense proportions. In addition, a faster rotating primordial Earth--while conserving the angular momentum of the Earth-Moon system--itself would have raised enormous tides that would have distributed the then existing continental landmasses around the equatorial region due to centrifugal effects, not to mention associated atmospheric and oceanic bulges.
Today the Moon is receding from Earth most probably at a decelerating rate, as compared to earlier ages. However, its influence on tectonic plate activity still remains intact, except at a much reduced pace. This inferred influence is based on the premise that our Earth-Moon complex should be examined as a binary planed system, with its barycenter (gravitational focus) some 1,600 km beneath Earth's surface. And, with the Earth's present-day diurnal rotation and the Moon's nominal [+ or -] 18 [degrees] elliptical orbit relative to Earth, a barrel-shaped volume of some 34 billion [km.sup.3] is continually being swept out deep within Earth's mantle somewhat below the asthenosphere by this constantly moving barycenter.
Much more volume would have been affected when the Moon was very close to Earth and in a far more pronounced elliptical orbit during those bygone days. In fact, even today, considerable heating due to tidal friction would be expected by this constantly moving barycenter, giving rise to convection currents and in effect resolving the enigma of its application to the subduction phenomena that causes seafloor spreading and which pushes one continent under another.
At the time of the Precambrian Period, some 600 million years past, there was an ice age of devastating severity--which geobiologist Joseph L. Kirschvink of California Technical Institute called Snowball Earth--that wiped out all but the hardest of microorganisms, and even these had to find protection somewhere as the ocean itself froze over. Evolution had a tough row to hoe, even without occasional asteroid impacts.
Now then, such tectonic activity over the eons, along with the recession of the Moon, induced a breakup of ancient Rodinia into continental fragments, that as a consequence would give rise to mountain-building processes, which in turn would affect weather and climatic conditions. Rodinia is the precursor of Pangea, and both supercontinents fragmented into smaller chunks by tectonic plate movements.
At any rate, a relatively nearby Moon, a somewhat faster rotating Earth, a collection of continental fragments in the equatorial zone, and concomitantly more massive seatides, all would contribute to erosion and carbonate uptake during preterprimordial geological epochs.
Carbon dioxide during this era is thought to comprise some 12% of Earth's atmosphere. And, not until oxygen-producing biota appeared did our planet become habitable for even the most primitive animal life. One might also expect a voluminous cloud cover to contribute to a highly reflective albedo during Earth's early age and contribute to the Snowball Earth ice age described in the "Scientific American" article and in "Rare Earth."
I respectfully suggest giving the Moon more credit in affecting tectonic plate activity than it has received heretofore. It is quite a rare event for any mention of the Moon in many geological processes, and effectively none for tectonic plate movement. Now, ain't that a shame.