The oldest rock yet found on earth

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The oldest rock yet found on earth (630, 632, 648) has an age close to four billion years, some six hundred million years younger than the earth itself. After reaching back to the earliest beginnings ( 63031), the story turns around and comes forward through the Archean Eon, while island arcs accrete and small cratons form (631-33). At the end of the Archean, in the very general neighborhood of 2.5 billion years before the present, great and unrepeatable changes occur in the behavior of the earth, including the precipitation of banded iron and the beginning of modern plate tectonics (634). In the early Proterozoic Eon, seven small cratons collide, conjoin as the Canadian Shield (633, 636-38). Younger island arcs eventually drift in and dock against the shield, forming large parts of Nebraska and Colorado (638-45). These  zakelijke energie novel views into Precambrian eons are the result of advances in radiometric dating ( 645-50) and, among other things, the measurement and interpretation of magnetic and gravity anomalies (651-54), all of it anchored and restrained by well cores (654-56). More arcs accrete. A coastal plate boundary like the Andean margin of South America develops along what is now a northeasterly trend through New Mexico and Kansas (650-51). About halfway through the Proterozoic, a baffling series of great plutons (each analogous to the Sierra Nevada batholith of relatively modern times) perforates North America from one side to the other and is mysteriously unaccompanied by the building of mountains, as plutons generally are, almost by definition (652-53). A time line at i.1 billion years comes in from the eastern and western margins of the continent and converges in the active and growing Midcontinent Rift (657-58). When the spreading stops under Iowa, the granites of Pikes Peak almost unaccountably appear in Colorado, the last tectonic event in Precambrian North America (660). An editor from whose counsel I have benefitted since the early zakelijke energie vergelijken phases of this project is Sara Lippincott, of Pasadena, California, who left The New Yorker in 1993 in order to become a free-lance editor of books. When Sara lived in New York, her idea of a perfect vacation was to get in an airplane and visit Caltech.

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