Geoscience Reference
In-Depth Information
One Small Step
On the evening of July 20, 1969, families around the world gathered in front of
their television sets, hoisting infants aloft so the youngsters could later claim they
had witnessed an event unique in human history, even in the history of the uni-
verse. Right on schedule, Astronaut Neil Armstrong (1930-2012) of
Apollo 11
stepped down from the Lunar Lander onto the surface of Mare Tranquillitatis.
Armstrong had conceived a memorable quote but in the emotion of the moment
did not deliver it perfectly, an outcome familiar to any public speaker, and he was
speaking to and for the entire human race. “That's one small step for a man, one
giant leap for mankind,” Armstrong had intended to say, but he forgot to include
the “a.” No matter; let us insert it for this courageous and modest pioneer who led
humanity to the Moon in an otherwise flawless mission.
When the
Apollo 11
sample box arrived back on Earth, instead of the shim-
mering crystals that the Greeks had imagined the Moon to be, scientists saw what
looked at first glance like dusty charcoal briquettes and at second glance like
deed were basalt, just as the alpha spectrometer data had indicated and Urey had
begrudgingly accepted. When scientists measured the age of the Tranquility Base
basaltsusingradiometric methods,theygot3.6billionyears,thesameasBillHart-
mann's estimate. Given that he had allowed that his parameters might be off by a
factor of four, Hartmann must have been as surprised as anyone.
Though outwardly like terrestrial basalts, internally the moon rocks turned out
to be surprisingly different. For one thing, they were bone dry. Geologists had nev-
er seen such unaltered, crystal-clear minerals under their microscopes. In a rare
moment of silliness, Urey had accepted the suggestion that the flat surfaces of the
maria might be attributable to the accumulation of lake sediments. But the absence
of water-bearing minerals in the lunar basalts put the quietus on that idea by show-
ing that the Moon had not only never had lakes, but, other than the ice that col-
liding comets might have delivered, it had never had even a single drop of water.
What process could leave the Earth wet and the Moon dry? Any successful theory
would have to solve that conundrum, one as fundamental as the Moon's angular
momentum and density.
