In the mid-1800s, Lord Kelvin estimated the age of the earth. Knowing that the earth's temperature increased an average of 1° Fahrenheit for each 50 feet of depth and assuming the earth began as molten rock at 7000° F, he calculated it took some 100 million years for the earth's temperature to reach its present day value. Working before knowledge of radioactivity, Lord Kelvin was far off in his calculations. The current scientific estimate is about 4.5 billion years.
Yet, the phenomenon that he used—the increase in heat with depth—holds
true as an approximate average. But as always, averages can be deceiving. Numerous hot
springs scattered throughout the Chihuahuan Desert attest to temperatures well above
those expectable at the source of the springs if the average is used. Most of these hot
springs, such as those at Truth or Consequences in the Rio Grande Valley, record
intruded bodies of once molten rock below; rock that only slowly gives up its heat over
thousands of years. Heat that someday may provide geothermal power for
electricity.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.