The deep hot biosphere. - Review - book reviews

Ecology, Sept, 1999 by David J. Thomas

Gold, Thomas. 1999. Copernicus/Springer-Verlag, New York. 225 pp. $27.00, ISBN: 0-387-98546-8 (alk. paper).

Thomas Gold presents interesting and controversial theories concerning the origins of petroleum hydrocarbons and the abundance of deep-subsurface microbial life in his book, The deep hot biosphere. Essentially, the book expounds upon ideas that Gold originally presented in a PNAS paper in 1992 (Proceedings of the National Academy of Sciences 89:6045-6049). Gold's book encompasses two general theses: 1) that the majority of Earth's hydrocarbons were entrapped during the coalescence of pre-planetary materials (not the metamorphic remains of past biomass), and 2) that these hydrocarbons provide the food source for a vast underground biosphere consisting of hyperthermophilic, hyperbarophilic microorganisms.

The first two chapters of the book provide an overview of the mainstream dogma of primordial evolution and the origin of subterranean microorganisms, which holds that subsurface life evolved after surface-based life. According to Gold (and others), life evolved not in surface oceans or ponds, but deep within the Earth's crust where it was protected from harsh ultraviolet radiation. Gold also argues that the deep subsurface provided food in the form of hydrocarbons for the first evolving cells. In the next several chapters, Gold presents and defends his theory that the world's petroleum resources come from relic, pre-planetary sources.

The prevailing theory of petroleum production states that "fossil fuels" are the result of the actions of extreme heat and pressure on buried biomass. Presumably, the biomass originated as plant and animal matter from millions of years ago that was buried in the sediments of lakes and oceans. Thus, petroleum reserves should be found in sedimentary formations. Gold cites numerous examples where petroleum deposits are found not in sedimentary formations, but in deep igneous formations, where according to mainstream Western thought, petroleum should not have formed. Gold reminds the reader that hydrocarbons abound in the solar system - the giant gas planets have enormous stores of methane and other light hydrocarbons, and many satellites of the outer planets appear to contain hydrocarbon ices. These hydrocarbons would have been dispersed throughout the cloud of debris that eventually accreted to form the solar system. If the outer planets kept their primordial hydrocarbons, might Earth have kept its hydrocarbons also? Gold thinks that it did, and that primordial hydrocarbons are largely responsible for present-day petroleum reserves. Gold also puts forth the idea that many, if not most, of the microorganisms found in petroleum samples are not contaminants, but natives of the subsurface. Gold notes that while his theory has been met with considerable skepticism in the Western Hemisphere, Eastern scientists have considered similar ideas for quite some time. During his research for the book, Gold found that he was not the first to propose the idea of a deep, hot biosphere. Russian (or ex-Soviet) scientists have pursued the idea for about one hundred years.

In later chapters, Gold suggests that movement of primordial hydrocarbons also may be responsible for earthquakes that occur away from fault lines, and that release of methane and other light hydrocarbons is a prelude to an earthquake. He cites mainly anecdotal historical evidence to support his hypothesis. He also recommends systematic monitoring of hydrocarbon outgassing as a means to predict earthquakes. Finally, in the last two chapters, Gold discusses how his "deep-earth gas theory" relates to the evolution of life on Earth and on Mars. If Earth retained primordial hydrocarbons and supports a deep-subterranean biosphere, might Mars have a similar subsurface biosphere? Gold presents a fairly detailed discussion of how subsurface life might have evolved on Mars. He also briefly states that the same could be true of other planets and planetary satellites.

On the whole, I found Gold's ideas very interesting. I admit that I am skeptical about Gold's deep-earth gas theory of petroleum origin, but I think that I am also a product of the mainstream Western dogma. He argues his points well and supports them with research published in well-respected journals (Science, Nature, PNAS, etc.). It is certainly reasonable to expect that if "chunks" of hydrocarbons were floating around in space with the rest of the pre-planetary debris, Earth may have a considerable store of subsurface hydrocarbons. Regardless of the source of hydrocarbons, the notion of extremophilic subsurface microorganisms is generally well accepted. The question then is whether subsurface microorganisms are a rare curiosity, or as Gold indicates, a part of a large and thriving biome. Only additional research will answer that question. The question of life on Mars and other planetary bodies is also still very much open to question. Although his discussion of possible Martian life was adequate, I would have liked to see more discussion about how his hypotheses relate to subsurface life on other planets.