The Geochron


Scientists from the University of Quebec recently announced the discovery of the oldest volcanic rocks ever found. The 3.825 billion year old rocks were discovered near Husdon Bay.

While these rocks may place a limit on the minimum age of the Earth, they can’t accurately date when the Earth itself was formed. Radiometric dating techniques though can be used to arrive at a surprisingly specific figure.

Dating at this time scale is based around the decay of various isotopes of uranium into lead: 238U to 206Pb, with a half life of 4.47 x 109 years, and 235U to 207Pb, with a half life of .707 x 109 years.

The decay curves of these isotopes relative to the stable isotope 204Pb can be used to form a linear equation, called The Geochron. The slope of this equation gives an age of the Earth of 4.55 ± 0.07 x 109 years.

These equations are fully developed in this excellent overview by Prof. Stephen A. Nelson of Tulane University.

» Posted: Monday, December 16, 2002 | Permanent Link