I have no memory on the first time I have heard of stromatolites, however, I have a very clear memory of their brief appearance on the game E.V.O. Stromatolites are mushroom-like structures resulting from the interaction between microorganisms and minerals in watery environment. They are a kind of Trace Fossil and they are used as models for the formation of some depositional systems.
Stromatolites are formed when algae and bacteria form a biofilm or a microbial mat underwater, mostly on the bottom. As the biofilm grows, sediments deposit over it and some minerals form within the biofilm causing it to lithify and forcing the microorganisms to move upwards no a new biofilm. This leaves a mineralized biofilm under the new one and the entire structure grows up. Stromatolites can have very complex structures, some of them so complex that they resemble living organisms; there is even a taxonomy for stromatolites.
Here I bring to you two approaches on stromatolite research. The first one is brought to us by Havemann & Foster (2008); they have collected some living stromatolites and tried to grow them in the lab. The second one is a numerical modeling of a stromatolite made by Drupaz et al. (2006) in order to understand how their morphology develops.
Living stromatolites can be found at Shark Bay (Australia) and some other place around the world. Havemann & Foster (2008) tried to replicate the environmental conditions found in these places and used biofilms brought from there to create stromatolites in vitro. The resulting structure cannot be called a stromatolite since it lacks the layered morphology typical of them (fig. 1). However, their work gave us insight on how the stromatolites form and organize. Their layered morphology is probably the result from the burial/dig up cycles found in their natural environment; a phenomenon which could not be recreated in the lab.
fig 1: The in vitro model showed main layers for the stromatolite: a crust, the cianobacteria layer and the biofilm itself. In the biofilm, most of the heterotrophic bacteria concentrate as the cianobacteria have a layer of their own. The crust is where the mineralization occurs and is probably where the microorganisms related to it are (from Havemann & Foster, 2008).
In order to create a numerical model one needs to see the stromatolite as a geochemical system powered by sunlight, where biological and environmental variables interact. In this system, the biological variables are the lesser-know and the model itself has showed that environmental variables like salinity, currents, nutrient distribution, granulometry and calcium concentration are the key factors for stromatolite formation. For instance, the currents regulate the nutrient distribution, which affects the biofilm growth and formation. Other point is that delicate columnar structures form only on calm and less disturbed currents while massive planar structures are prone to be found on turbulent and deeper waters. Simpler morphologies are less dependent of the biological variables and can be resulting of solely inorganic/geochemical processes while complex morphologies are strongly related to biological variables.
fig 2: Here we have many know stromatolite morphologies as they were first described and as Dupraz et al. (2006) recreated them using their model.
So, how such research can be useful? By understanding how such structures grow, we can make predictions on how their environment work. This has implications on current environments and on palaeoenvironments as well, where oil reservoirs can be formed. Understanding such deposits allow us to create safer and more efficient oil exploration technologies. On the other hand, both methods have limitations. For instance, in vitro models have time and space constrains, they also alter the composition of the community in the culture somehow and some environmental variables (like the burial cycle) are hard to recreate. Meanwhile the in silica model is constrained on how many variables can be modeled or understood at the same time.
Andres, M., & Pamela Reid, R. (2006). Growth morphologies of modern marine stromatolites: A case study from Highborne Cay, Bahamas Sedimentary Geology, 185 (3-4), 319-328 DOI: 10.1016/j.sedgeo.2005.12.020
Batchelor, M., Burne, R., Henry, B., & Watt, S. (2000). Deterministic KPZ model for stromatolite laminae Physica A: Statistical Mechanics and its Applications, 282 (1-2), 123-136 DOI: 10.1016/S0378-4371(00)00077-7
Dupraz, C., Pattisina, R., & Verrecchia, E. (2006). Translation of energy into morphology: Simulation of stromatolite morphospace using a stochastic model Sedimentary Geology, 185 (3-4), 185-203 DOI: 10.1016/j.sedgeo.2005.12.012
Havemann SA, & Foster JS (2008). Comparative characterization of the microbial diversities of an artificial microbialite model and a natural stromatolite. Applied and environmental microbiology, 74 (23), 7410-21 PMID: 18836014