Stromatolites are rock-like structures built by microbes (single-celled cyanobacteria, also known as blue-green algae). Shark Bay’s stromatolites are only 2,000 to 3,000 years old, but they are similar to life forms found on Earth up to 3.5 billion years ago! They provide a unique insight into what the world was like at the dawn of time. Canon EOS 400D, ISO 200, Exposure Time: 1/400, Lens Model: EF-S18-55mm f/3.5-5.6, Adobe Lightroom 3. Photo: Drew Barrett