For centuries and lacking significant evidence to the contrary, much of the Western world thought that an omnipotent god specially created the earth and the first humans over a period of a few days. This conclusion was derived from interpretations of certain sacred texts, particularly the Bible, which was then thought to be the source of all truth about nature and the universe that surrounds us. Given these "facts", then, it was not entirely unreasonable to believe that humanity is at the center of the universe and arrived on the scene at the beginning of time, only a few thousand years ago. In the seventeenth and eighteenth centuries, however, a few inquisitive and enterprising souls began to realize that there was a great deal of information about the history of earth and its cosmic surroundings recorded in the stars and in the rocks, and what we know today as science was born. Gradually, over the next few centuries, careful observations and rational experiments replaced myth and theology as the best source of information about the physical history of the universe. Pascal Richet, a Senior Geophysicist at the Institut de Physique du Globe de Paris, and a distinguished scientist, guides us through the critical events of this transition.
This is not a book about the age of the earth and the cosmos. Rather, it is an accounting of the history and development of people's thinking about, and exploration of, deep time. Richet takes the reader on a grand adventure that begins at the time of ancient Egypt and ends in 1953, when Clair Patterson made the first reliable measurements of the age of meteorites and showed convincingly that the earth was probably of the same age of 4.5 billion years. Patterson's historic result, however, was not the end of the story but only a new beginning of a quest that has resulted in a rich and detailed knowledge of the history of the earth, the solar system, and the universe. The reader will have to go elsewhere for the discoveries of the past half-century, but fortunately that story is readily available in other recent texts.
In some passages of this fascinating history, Richet does not quite flesh out the story. For example, we learn all of the essentials (minus the mathematics) about Lord Kelvin's calculations based on heat flowing from the earth's crust and the effect that Kelvin's work had on the understanding of deep time for more than a half century. But Richet never really tells us enough about why Kelvin's calculations were wrong and why heat flow considerations could not (and still cannot) reveal the age of the earth, so the reader is left wondering where Lord Kelvin, arguably the most prominent physicist of his day, went wrong. In other passages, in contrast, Richet explores subjects in satisfyingly rich detail. For example, he leads the reader through the initial discovery and gradual understanding of heat and how widely ranging this new knowledge impacted not just geology but physics and other fields of science and engineering as well. One of the things I like a lot about this book is Richet's ability to show how and why seemingly unrelated discoveries in physics rapidly influenced important discoveries in geology and geophysics.
Here and there throughout the text are whimsical asides that are not only fun but also truly expand our insights about the science and the scientists of the day. My favorite can be found on pages 256–8, where Richet discusses the connection between the Big Bang theory and the Martians. He recounts the story of Percival Lowell (1855–1916), the mathematician turned businessman turned astronomer who built the Lowell Observatory on a mountain peak near Flagstaff, Arizona. Lowell was fascinated by the earlier reports of continents, seas, and canals on Mars, and spent much of his astronomical career studying that planet and writing about its presumed inhabitants. It was at the Lowell Observatory in 1912 that VM Slipher first observed the red shift in the light from distant galaxies and correctly interpreted it as evidence that the other galaxies were moving away from the Milky Way galaxy in all directions, that is, that the universe was expanding. The expansion, or more properly inflation, of the universe is one way in which the age of the universe is measured and is the original basis for the Big Bang theory. Richet concludes, with tongue in cheek, "The now classic Big Bang theory and the age of the universe thus owe something, at least indirectly, to the Martians."
For a translation, this is a surprisingly smooth read, and the rare turgid passages do not really detract from the overall quality of the prose. Overall, I found this to be a satisfying and easy read as well as an approach to the telling of a fascinating story that I have not encountered in any other book. Richet has kindly left out the mathematics of the subject and the book is devoid of complicated graphs. The result is a book that even readers with only a modest understanding of science will find easy to read, yet which is rich enough in its narrative to satisfy even the most knowledgeable specialist.