...igneous activity (both extrusive and intrusive) occurred in the Caledonian mountain belt, which stretched from New England, Nova Scotia, Newfoundland, Scotland, and Scandinavia to eastern Greenland.Radiometric dating of granitic intrusions associated with the Caledonian orogeny yields ages between about 430 million and 380 million years.One new and fundamental result has come from radiometric age dating of the samples.When a rock cools from the molten to the solid state, its radioactive isotopes are immobilized in mineral crystal lattices and then decay in place.The igneous activity that produced such intrusions......calculation was based on the assumption that the substance of the Earth is inert and thus incapable of producing new heat.As a result of their longevity, they are still present in meteorites and on Earth, and they are commonly used for dating rocks and meteorites.
Studies of isotopes formed from the decay of radioactive parent elements with short half-lives, in both lunar samples and meteorites, have demonstrated that the formation of the inner planets, including Earth, and the Moon was essentially complete within 50 million years after the interstellar cloud region collapsed.
During the 1950s and ’60s, isotopic dating of rocks showed that the crystalline massifs of Precambrian age (from about 4 billion to 541 million years ago) found on opposite sides of the South Atlantic did indeed closely correspond in age and composition, as Wegener had surmised.
It is now evident that they originated as a single assemblage of Precambrian continental nuclei...
Scientific knowledge of Earth’s geologic history has advanced significantly since the development of radiometric dating, a method of age determination based on the principle that radioactive atoms in geologic materials decay at constant, known rates to daughter atoms.
Radiometric dating has provided not only a means of numerically quantifying geologic time but also a tool for determining the...