WhatWhat aarere ""Stromatolites"?Stromatolites"? LivingLiving StromatolitesStromatolites WhyWhy SStudytudy Stromatolites?Stromatolites? StromatolitesStromatolites aarere llivingiving eexamplesxamples ooff For years, living stromatolites were thought to be extinct. The LivingLiving stromatolitesstromatolites aarere aann iidealdeal earth'searth's eearliestarliest rreefs.eefs. only information about stromatolites came from fossils in the modelmodel ssystemystem fforor sstudyingtudying biological-biological- rock record. Then, in the 1960's, modern stromatolites were geologicalgeological iinteractions.nteractions. Stromatolites form an unusual and special type of reef. Unlike found in Shark Bay, Australia, where the seawater is too salty most present-day reefs, which are composed of coral, for most animals and plants to survive. These harsh Stromatolites form a compact ecosystem that is elegant in stromatolites are formed by microorganisms. These micro- environmental conditions allow stromatolite-building simplicity. Three distinct microbial communities are organisms trap and bind sand grains together and/or microorganisms to become the dominant community. responsible for the growth of these layered reefs. Initially, precipitate calcium carbonate to form laminated mounds of hair-like filamentous cyanobacteria trap and bind sediment limestone. The layered internal structure of these reefs is a BahamianBahamian SStromatolitestromatolites (A). Subsequently, the surface becomes colonized with a characterisitc feature and, indeed, the name 'stromatolite' in In the 1980's, stromatolites were discovered in Schooner Cays, slimy coating (biofilm), which precipitates a thin crust of Greek means 'layered rock'. Bahamas, growing in an open marine environment. Living limestone (B). Finally, coccoid (spherical) cyanobacteria Stromatolites are rare in today's oceans. However, they can stromatolites have since been found in several localities along colonize the surface immediately below the thin limestone be found in several localities along the margins of Exuma the margins of Exuma Sound, including Lee Stocking Is., crust (C). These coccoid cyanobacteria bore into the sand Sound. The Bahamian stromatolites are living examples of Stocking Is., Highborne Cay, and Exuma Land & Sea Park. At all grains, and alter them into a hard-cemented layer. Earth’s earliest reefs. of these sites, stromatolites are frequently buried by shifting Eventually, filamentous cyanobacteria re-colonize the surface sand, which excludes growth of advanced reef organisms, that and the cycle begins again. The subsurface, layered portion of would otherwise overgrow or disrupt the stromatolites. the stromatolite is 'fossilized', non-living rock, with each layer Bahamian stromatolites typically grow as mounds or columns. representing a former surface mat. Studies of this simple The stromatolite surface is a living microbial mat. Carbon system provide models for biogeochemical cycling, isotope dates indicate that stromatolites in the Stocking Island population dynamics, and mineral formation in modern and reef complex began forming 1000-2000 years ago. ancient environments. FossilFossil andand livingliving stromatolitesstromatolites aarere anan A B C Living stromatolite reef complex, Stocking Island importantimportant ssourceource ooff iinformationnformation oonn tthehe earlyearly developmentdevelopment ofof lifelife onon earthearth aandnd possiblypossibly ootherther pplanets.lanets.

4 cm 1 mm 100 µm 50 µm 100 µm Microscopic images of the three microbial communities forming Exuma stromatolites.

A 20 cm B C HighborneHighborne CayCay ResearchResearch SStationtation Stromatolites viewed underwater (A) and in vertical cut Earth 3 billion years ago (Smithsonian Mural) section (B,C); C is microscope image of surface mat. StromatolitesStromatolites aandnd EEartharth HHistoryistory RIBSRIBS Stromatolites are the oldest known macrofossils, dating back A major goal of RIBS is to understand fundamental processes over 3 billion years (Earth is ~4.5 billion years old). and biological-geological interactions in the three billion year- Dominating the fossil record for 80% of our planet's history, old stromatolite ecosystem. Researchers adopt stromatolites formed massive reefs in Earth's primitive multidisciplinary approaches. Microbiological, geochemical oceans. and sedimentological analyses based on a variety of novel and To conduct field studies, the Research Initiative on Bahamian innovative techniques are integrated in field and lab-based Stromatolites operates a research station on Highborne Cay. Scientists believe that the photosynthetic activity of studies. The results will have significant implications for cyanobacteria, the most important group of stromatolite- From here, resident scientists observe stromatolite understanding such fundamental issues as the evolution of life, development on a continuing basis. forming microorganisms, generated the oxygen in our the dynamics of sedimentation, and the flow of energy and Instruments in the water measure wave energy and sea atmosphere. An oxygen-rich environment was critical to the matter through the Biosphere. development of higher forms of life on Earth. surface temperature. A weather station provides data on The Research Initiative on Bahamian Stromatolites (RIBS) is wind speed, wind direction, air temperature, and light. After a long global dominance, stromatolites suffered a conducting an active research program. The RIBS team includes dramatic decline in abundance starting ~700 million years Stromatolite surfaces are marked to correlate growth with sedimentologists, microbiologists, geochemists, and biological environmental conditions. ago. This decline, which led to the near disappearance of oceanographers from several US institutions, including The laboratory provides space to process samples, calibrate stromatolites, has been attributed to various factors, ranging University of Miami, U. Connecticut, U. South Carolina, equipment, and perform data analysis. Microscopes are used from the evolution of competing organisms (plants and Duquesne, U. of Maryland, U. North Carolina, U.C. Davis, for field identification of microbial assemblages; microsensors animals) to changes in ocean chemistry. Smithsonian Institution, and NASA Ames as well as European provide data on geochemical gradients. institutions from Switzerland, Scotland and the Netherlands.