Alexander P. Petroff a,1, Min Sub Sim a, Andrey Maslov b, Mikhail Krupenin b, Daniel H. Rothman a, and Tanja Bosak a
-Author Affiliations
aDepartment of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139; and
bZavaritskii Institute of Geology and Geochemistry, Ural Division, Russian Academy of Sciences, Pochtovyi per. 7, Yekaterinburg 620151 Russia
Edited by Paul F. Hoffman, Harvard University, Cambridge, MA, and approved April 15, 2010 (received for review February 18, 2010)
Abstract
Stromatolites may be Earth’s oldest macroscopic fossils; however, it remains controversial what, if any, biological processes are recorded in their morphology. Although the biological interpretation of many stromatolite morphologies is confounded by the influence of sedimentation, conical stromatolites form in the absence of sedimentation and are, therefore, considered to be the most robust records of biophysical processes. A qualitative similarity between conical stromatolites and some modern microbial mats suggests a photosynthetic origin for ancient stromatolites. To better understand and interpret ancient fossils, we seek a quantitative relationship between the geometry of conical stromatolites and the biophysical processes that control their growth. We note that all modern conical stromatolites and many that formed in the last 2.8 billion years display a characteristic centimeter-scale spacing between neighboring structures. To understand this prominent—but hitherto uninterpreted—organization, we consider the role of diffusion in mediating competition between stromatolites. Having confirmed this model through laboratory experiments and field observation, we find that organization of a field of stromatolites is set by a diffusive time scale over which individual structures compete for nutrients, thus linking form to physiology. The centimeter-scale spacing between modern and ancient stromatolites corresponds to a rhythmically fluctuating metabolism with a period of approximately 20 hr. The correspondence between the observed spacing and the day length provides quantitative support for the photosynthetic origin of conical stromatolites throughout geologic time.
geobiology photosynthesis cyanobacteria microbialite
Footnotes
1To whom correspondence should be addressed. E-mail: petroffa@mit.edu.
Author contributions: A.P.P., A.M., D.H.R., and T.B. designed research; A.P.P., M.S.S., M.K., and T.B. performed research; A.P.P. and D.H.R. analyzed data; and A.P.P., D.H.R., and T.B. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1001973107/-/DCSupplemental.
Freely available online through the PNAS open access option.
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