This chapter completes the story of the acceptance of plate tectonics, which marks the beginning of the modern period of Earth system science. This final approval required additional contributions by several researchers, with the key papers being published in 1968. Jason Morgan’s work on crustal blocks, of which he had given an impromptu preview at the American Geophysical Union in April 1967, proposed that on Earth’s dynamic surface 20 crustal blocks move relative to each other, endlessly jostling for their place in the jigsaw. Simultaneously, Xavier Le Pichon, a young French geophysicist who worked with the Ewing brothers at Lamont Geological Observatory from 1963 to 1989, connected the kinematic ideas of Morgan, McKenzie and Parker to the vast data sets held at Lamont, particularly the magnetic profiles. Le Pichon’s computer model demonstrated that the motion of six large rigid blocks completed a jigsaw that covered most of Earth and could accurately account for the evolution of ocean basins. His model of June 1968 indicated that plates do indeed form an integrated system in which the sum of all crust generated along 50,000 kilometres of ocean ridges equals the cumulative amount destroyed in the subduction zones.1