Age of Meteorites and the Earth

Age of Meteorites and the Earth
The centerpiece of this section is the Clare Patterson study “Age of Meteorites and the Earth” (Geochimica et Cosmochimica Acta, 1956) that marked the Earth as 4.55 billion years old; an age that has stood ever since. The elegance of Patterson’s approach is revealed by the simple lines drawn on the graph shown here. The two axes of the graph are ratios of different varieties or “isotopes” of lead. Each isotope has the same number of positively charged protons (hence, defining the element as lead) in the atomic nucleus, but a slightly different number of neutrally charged neutrons. The 82 protons, plus the numbers of neutrons that range from 122 to 125, give the different isotopes of lead their names: 204Pb, 206Pb, and 207Pb. The number of atoms of 204Pb is constant throughout time, but the number of atoms of 206Pb and 207Pb has been steadily increasing since the Earth first formed as different isotopes of uranium have undergone radioactive decay. Patterson’s great insight was that, if he analyzed the different amounts of 204Pb, 206Pb, and 207Pb in different meteorites, the primordial building blocks of planets, then their lead ratios should fall on a straight line, with the slope of the line providing the age of the Earth. Patterson regressed two lines, one that gave an age of 4.6 billion, the other 4.5 billion. He split the difference and arrived at 4.55 billion. Patterson’s age raised intriguing questions of its own though, because he was providing an age for Earth’s building material (meteorites), not directly the age of the Earth itself. Put in another fashion, is it appropriate to think of the age of a building as when it is finally completed, or rather when its first corner stone is laid?
Call Number (click link to view in library catalog)
551.05 GEOC
Patterson, Clare
Oxford, New York Pergamon Press
Oxford, New York
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Bibliographic Citation
Patterson, Clare. “Age of Meteorites and the Earth”. Geochimica et Cosmochimica Acta 10 (1956): 230-237.