The content you've requested is available without charge only to active Sigma Xi members and
If you are an active member or an individual subscriber, please log in now in order to access this article.
If you are not a member or individual subscriber, you can:
The mathematical physicist Lord Kelvin produced one of the 19th century's most famous estimates of the age of the Earth: some 100 million years. The Earth is, in actuality, about 4.5 billion years old. Kelvin's result was based on the idea that the near-surface geothermal gradient reflects the conductive cooling of the solid Earth from an initial state of uniformly high temperature. Today many scientists, including professional geologists, believe that Kelvin's age was off because he was unaware that heat is generated within the Earth by radioactive decay (radioactivity not yet having been discovered). In fact, Kelvin's error, as his one-time assistant John Perry pointed out in 1895, was to regard the rocky mantle of the Earth as being rigid, whereas geologists now know that it is a viscous fluid that transfers heat by convection.
This article is adapted with permission of the Geological Society of America from a paper by England, Molnar and Richter, "John Perry's neglected critique of Kelvin's age for the Earth: A missed opportunity in geodynamics," which appeared in the January 2007 issue of GSA Today.
Connect With Us:
An early peek at each new issue, with descriptions of feature articles, columns, and more. Every other issue contains links to everything in the latest issue's table of contents.News of book reviews published in American Scientist and around the web, as well as other noteworthy happenings in the world of science books.
To sign up for automatic emails of the American Scientist Update and Scientists' Nightstand issues, create an online profile, then sign up in the My AmSci area.
JSTOR, the online academic archive, contains complete back issues of American Scientist from 1913 (known then as the Sigma Xi Quarterly) through 2005.
The table of contents for each issue is freely available to all users; those with institutional access can read each complete issue.
View the full collection here.
Receive notification when new content is posted from the entire website, or choose from the customized feeds available.