Ancient Earth, Ancient Skies: The Age of Earth and its Cosmic Surroundings

by G. Brent Dalrymple

This book is a well-presented examination of how science has come to determine, with a startling degree of accuracy, the age of the Earth, the solar system and ultimately the universe itself. The book is actually a distillation of the author’s earlier, more scholarly work The Age of the Earth, targeted for a more general audience. Disappointingly, in reaching for this general audience, it is nearly devoid of any mathematics at all, which (I assume) the editors felt would “scare off” readers. That frustration aside, the book is an eye-opening introduction to the scientific triumph of radiometric dating and how it has been used to expose large-scale cosmic events across deep time.

After an interesting overview of earlier approaches to the problem, such as terrestrial cooling and erosion analysis, he explains the fundamentals behind radioactive decay and how it can be used as a reliable clock over enormous expanses of time. The decay rates of radioactive isotopes have been shown to be independent of temperature, pressure and chemical reaction which means their decay held steady through the cauldron of the early solar system.

Careful analysis of the decay of various elements into specific “daughter” isotopes is shown to reveal in detail, the time of the formation of the first debris from the solar nebula (4.556 ± .002 billion years ago), 50 million years before the nuclear ignition of the sun itself. Evidence of lava flows on the earliest proto-planets can be discerned and a basic time line of the development of the inner solar system is mapped out, all from the dating of mineral inclusions. Dalrymple’s excitement over this culmination of years of work comes through in his writing.

For those interested in the math behind radiometric dating, there is an excellent overview by Prof. Stephen A. Nelson of Tulane University here.