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PNAS | February 27, 2001 | vol. 98 | no. 5 | 2148-2153
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Special Feature
Geology
 Oxygen isotope ratios of PO4: An inorganic indicator of enzymatic activity and P metabolism and a new biomarker in the search for life

Ruth E. Blake*,dagger , Jeffrey C. AltDagger , and Anna M. Martini§

* Department of Geology and Geophysics, Yale University, New Haven, CT 06520-8109; Dagger  Department of Geology, University of Michigan, Ann Arbor, MI 48109; and § Department of Geology, Amherst College, Amherst, MA 01002

Edited by Karl K. Turekian, Yale University, New Haven, CT, and approved December 29, 2000 (received for review October 29, 2000)

The distinctive relations between biological activity and isotopic effect recorded in biomarkers (e.g., carbon and sulfur isotope ratios) have allowed scientists to suggest that life originated on this planet nearly 3.8 billion years ago. The existence of life on other planets may be similarly identified by geochemical biomarkers, including the oxygen isotope ratio of phosphate (delta 18Op) presented here. At low near-surface temperatures, the exchange of oxygen isotopes between phosphate and water requires enzymatic catalysis. Because enzymes are indicative of cellular activity, the demonstration of enzyme-catalyzed PO4-H2O exchange is indicative of the presence of life. Results of laboratory experiments are presented that clearly show that delta 18OP values of inorganic phosphate can be used to detect enzymatic activity and microbial metabolism of phosphate. Applications of delta 18Op as a biomarker are presented for two Earth environments relevant to the search for extraterrestrial life: a shallow groundwater reservoir and a marine hydrothermal vent system. With the development of in situ analytical techniques and future planned sample return strategies, delta 18Op may provide an important biosignature of the presence of life in extraterrestrial systems such as that on Mars.

dagger To whom reprint requests should be addressed. E-mail: blake{at}geology.yale.edu

www.pnas.org/cgi/doi/10.1073/pnas.051515898
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This article has been cited by other articles in HighWire Press-hosted journals:


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A. S. Colman, R. E. Blake, D. M. Karl, M. L. Fogel, and K. K. Turekian
Marine phosphate oxygen isotopes and organic matter remineralization in the oceans
PNAS, September 13, 2005; 102(37): 13023 - 13028.
[Abstract] [Full Text] [PDF]