Stromatolites are living fossils and the oldest living lifeforms on our planet. stromatolites are stony structures built by colonies of microscopic photosynthesizing organisms called cyanobacteria. As sediment layered in shallow water, bacteria grew over it, binding the sedimentary particles and building layer upon millimetre layer until the layers became mounds. Using the sun to harness energy, they produced and built up the oxygen content of the Earth’s atmosphere to about 20%, giving the kiss of life to all that was to evolve. How is the living age calculated ?