longer), it transferred some of its angular momentum to the Moon, flinging it
outward into a widening orbit. Eventually, the Moon’s orbit gradually
widened to 240,000 miles away. Even today, the Moon is still receding from
the Earth about an inch or so each year.
The presence of a rather large moon, the biggest in relation to its
mother planet, the two forming a twin planetary system, might have had a
major influence on the initiation of life.The unique properties of the Earth-
Moon system raised tides in the ocean. Cycles of wetting and drying in tidal
pools might have helped Earth acquire life much earlier than previously
thought possible.
The Moon might also have been responsible for the relatively stable cli-
mate, making Earth hospitable to life by stabilizing the tilt of the planet’s rota-
tional axis, which marks the seasons.Without the Moon, life on Earth would
likely face the same type of wild fluctuations in climate that Mars has appar-
ently experienced through the eons. If its spin axis were no longer maintained
by the Moon, in only a few million years Earth would have drastically altered
its tilt sufficiently to make the polar regions warmer than the Tropics.Figure 8A Moon
rock brought back by
Apollo 16.
(Photo courtesy NASA)
Historical Geology