Scientific Colloquium
March 5, 2004

The second half of the 20th century saw two historic scientific developments:  the achievment of space flight and the emergence of the theory of plate tectonics.  These superficially independent events are much more closely related than most scientists realize.   This lecture will summarize major discoveries from space research, both terrestrial and extraterrestrial, and demonstrate their relation to plate tectonic theory.  Examples will include sea-surface altimetry, direct measurement of plate rigidity and plate motion, remote sensing of continental areas, discovery of folded mountains on Venus (a planet with no plates), and evidence that even small bodies like the Moon have undergone early global differentiation, forming crusts analogous to the continental crust of the Earth.  Plate tectonic theory has been essentially confirmed by space research, but it has also been found at least incomplete, if not incorrect, in several respects.