title: Morphological record of oxygenic photosynthesis in conical stromatolites.
abstract: Conical stromatolites are thought to be robust indicators of the presence of photosynthetic and phototactic microbes in aquatic environments as early as 3.5 billion years ago. However, phototaxis alone cannot explain the ubiquity of disrupted, curled, and contorted laminae in the crests of many Mesoproterozoic, Paleoproterozoic, and some Archean conical stromatolites. Here, we demonstrate that cyanobacterial production of oxygen in the tips of modern conical aggregates creates contorted laminae and submillimeter-to-millimeter-scale enmeshed bubbles. Similarly sized fossil bubbles and contorted laminae may be present only in the crestal zones of some conical stromatolites 2.7 billion years old or younger. This implies not only that cyanobacteria built Proterozoic conical stromatolites but also that fossil bubbles may constrain the timing of the evolution of oxygenic photosynthesis.
authors: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. tbosak@mit.edu
authors: Tanja
authors: T
authors: Bosak
authors: Biqing
authors: B
authors: Liang
authors: Min Sub
authors: MS
authors: Sim
authors: Alexander P
authors: AP
authors: Petroff
mesh_terms: D001105:Archaea / Q000378:metabolism; D005580:Fossils; D019015:Geologic Sediments / Q000382:microbiology*; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis
chemical_list: D010100:Oxygen