The age of the Earth in the twentieth century:: a problem (mostly) solved
Published:January 01, 2001
In the early twentieth century the Earth’s age was unknown and scientific estimates, none of which were based on valid premises, varied typically from a few millions to billions of years. This important question was answered only after more than half a century of innovation in both theory and instrumentation. Critical developments along this path included not only a better understanding of the fundamental properties of matter, but also: (a) the suggestion and first demonstration by Rutherford in 1904 that radioactivity might be used as a geological timekeeper; (b) the development of the first mass analyser and the discovery of isotopes by J. J. Thomson in 1914; (c) the idea by Russell in 1921 that the age of a planetary reservoir like the Earth’s crust might be measured from the relative abundances of a radioactive parent element (uranium) and its daughter product (lead); (d) the development of the idea by Gerling in 1942 that the age of the Earth could be calculated from the isotopic composition of a lead ore of known age; (e) the ideas of Houtermans and Brown in 1947 that the isotopic composition of primordial lead might be found in iron meteorites; and (f) the first calculation by Patterson in 1953 of a valid age for the Earth of 4.55Ga, using the primordial meteoritic lead composition and samples representing the composition of modern Earth lead. The value for the age of the Earth in wide use today was determined by Tera in 1980, who found a value of 4.54 Ga from a clever analysis of the lead isotopic compositions of four ancient conformable lead deposits. Whether this age represents the age of the Earth’s accretion, of core formation, or of the material from which the Earth formed is not yet known, but recent evidence suggests it may approximate the latter.
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The Age of the Earth: From 4004 BC to AD 2002
The age of the Earth has long been a subject of great interest to scientists from many disciplines, particularly geologists, biologists, physicists and astronomers. This volume, The Age of the Earth: from 4004 BC to AD 2002, brings together contributors from these different subjects, along with historians, to produce a comprehensive review of how the Earth’s age has been perceived since ancient times. Touching on the works of eminent scholars from the seventeenth to nineteenth centuries, it describes how concepts of the Earth’s history changed as geology slowly separated itself from religious orthodoxy to emerge as a rigorous and self-contained science. Fossils soon became established as useful markers of relative age, while deductions made from geomorphological processes enabled the discussion of time in terms of years. By the end of the nineteenth century biologists and geologists were fiercely debating the issue with physicists who were unwilling to give them the time needed for evolution or uniformitarianism.
With the discovery of radioactivity, attempts to calculate the Earth’s age entered a new era, although these early pioneers in radiometric dating encountered many difficulties, both technical and intellectual, before the enormity of geological time was fully recognized. This effort affected both the theory and practice of geology. Geochronology was largely responsible for it maturing into a professional scientific discipline, as increasingly refined techniques measured not only the age of the rocks, but the rate of processes which now elucidate many aspects of the Earth’s evolution.
Even today the Earth’s chronology remains a contentious topic — particularly for those dating the oldest rocks — and it is implicated in debates surrounding our hominid ancestors, the origins and development of life, and the age of the universe.
The Age of the Earth: from 4004 bc to AD 2002 will be of particular interest to geologists, geochemists, and historians of science, as well as astronomers, archaeologists, biologists and the general reader with an interest in science.