Thinking about the Earth: A History of Ideas in Geology

Thinking about the Earth: A History of Ideas in Geology

by David R. Oldroyd
Cambridge, MA: Harvard University Press, 1996. Pp. xxx + 410. Hardback.

Thinking about the Earth traces the history of ideas about the planet we live on from ancient times to the present. The volume reviews concepts concerning the origin of the Earth, its physical and chemical composition, its surface and tectonic evolution, its history of climate change, and interactions with its biosphere.

The book is largely nontechnical and, hence, should be easily accessible to the educated nonspecialist. The author, David Oldroyd, is a professor at the University of New South Wales, Australia, specializing in the history of geology, and the book is very much what might be expected from a science historian. The volume is very well researched, and even relatively minor players in some of the major debates in the Earth sciences during the last two centuries arc accorded their fifteen lines in the limelight.

The book will be of value to anyone in, retested in the development of ideas concerning Earth history, but its coverage of most topics trails off with work from the 1950s to 1960s and it does not attempt to track more recent developments. However, Oldroyd's goal is clearly not to provide an up-to-date review of scientific research but rather to illustrate the historical development of ideas concerning the Earth, and in this regard he succeeds admirably.

A weakness of the volume is that Oldroyd is not willing to admit that certain older ideas about the Earth are demonstrably incorrect and have been conclusively rejected by the Earth sciences community. Indeed, science docs progress with time, consigning some ideas to the trash heap of history.

To give an example, the Earth was once generally held to be the center of the cosmos, about which all other heavenly bodies revolved. This anthropocentric view was subsequently demolished by Newtonian mechanics, which explained the motion of the Earth about the Sun, that of the solar system about the Milky Way galaxy, and that of galaxies through the vastness of intergalactic space as a function of gravitational dynamics. Because Newtonian mechanics is solidly grounded in the laws of physics, a return to a Ptolemaic cosmos is a virtual impossibility.

An analogous case in Oldroyd's volume concerns the face-off between the expanding Earth and plate tectonic hypotheses. Both hypotheses were initially constructed to account for the distribution of continents and oceans on the Earth's surface. According to the expanding Earth hypothesis, the terrestrial sphere once had a solid sialic crust which subsequently split into fragments (i.e., the modern continents) that became separated by ocean basins as the Earth expanded.

The primary problem with this hypothesis is that there is simply no physical mechanism by which the Earth could have expanded by the requisite amount, i.e., roughly a three-fold increase in surface area and more than a five-fold increase in volume. Plate tectonic theory, which I will refrain from discussing here, now has a wealth of geophysical and geochemical evidence in support of it, and the expanding Earth hypothesis has about as much chance of resurrection as a Ptolemaic cosmos.

Philosophically, the point overlooked in Oldroyd's position that current views of the Earth have no greater intrinsic merit than earlier views is that scientific concepts have not merely changed through time but have deepened. By this, I mean that the level of debate has progressed from problems of a broad, fundamental nature to problems that are much more narrowly focused as more information has been generated and analyzed.

As an example, as recently as thirty years ago a major debate within the scientific community concerned the tempo of the evolution of life, i.e., whether it occurred gradually and continuously (as envisioned by Darwin) or whether it occurred episodically following long periods of stasis (the more recent "punctualist" view). Detailed compilations of taxonomic data have led to a widespread consensus among Earth scientists in favor of punctualism, and current research focuses on the factors permitting long-term evolutionary stasis (e.g., "homeostasis," or self-regulating equilibria within biotic communities) as well as those responsible for precipitating rapid evolutionary change (most of which appears to be associated with mass extinction events).

Hence, ideas on a given issue may fluctuate for some period of time, but in most cases enough darn is eventually generated to resolve the issue and scientific debate progresses to a deeper, more detailed level.

In the final section of the book, Oldroyd considers the Gaia hypothesis, one of the most interesting and controversial ideas to tweak established scientific paradigms in recent years. Since its inception, the Gaia hypothesis has fissioned into several versions, reflecting varying emphasis on the holistic, oneness-with-Mother-Earth theme. In the original version published by James Lovelock, the essence of the Gaia hypothesis is that the biosphere has a stabilizing influence on Earth-surface conditions, and that such stability, in turn, promotes a healthy, well-integrated biosphere.

The negative reaction of the scientific community to the Gaia hypothesis resulted, I think, largely from its avid acceptance by New Ager's, who have favored more holistic versions in which the Earth itself is viewed as a living organism. However, the Earth was sterile at some point in the past and will be so again at some point in the future, and it is nothing more nor less than a solid physical substrate on which life has developed (or been introduced) and to which life constantly adapts itself. To his credit, Oldroyd gives a very balanced account of the original Gaia hypothesis and of its potential implications with regard to long-term interactions between the Earth and its biosphere.


Spring 1998