the Strelley Pool formation stromatolites

Dating back an astonishing 3.43 billion years to the Paleoarchean Era, the stromatolites of the Strelley Pool Formation in Pilbara, Western Australia, represent some of the oldest widely accepted evidence of life on Earth. Rather than the fossilised remains of a single creature, these structures are trace fossils of ancient, complex microbial mats—predominantly composed of photosynthetic cyanobacteria—that thrived in a shallow, prehistoric sea. As tides washed over these sticky colonies, fine sediments became trapped in the microbial goo. To survive, the microbes grew upward toward the sunlight. Only the very top, ultra-thin skin of the stromatolite—often just a few millimeters thick—was actually alive. This top layer was packed with photosynthesising microbes that needed to stay exposed to the sun. Repeating this cycle of growth over generations, these stromatolites built up the distinctive, undulating mineral layers now preserved forever in iron-rich chert.

The Strelley Pool stromatolites hold monumental importance in the scientific community, offering a rare window into our planet's infancy. Emerging long before Earth had an oxygen-rich atmosphere, these ancient organisms were among the evolutionary pioneers that helped pave the way for complex life to eventually evolve. Today, because early Earth and early Mars shared very similar environments, these specific rock formations are used by NASA astrobiologists as a primary geological blueprint. By studying the chemical signatures and varied structural patterns of these Pilbara fossils, scientists know exactly what to look for when searching for signs of ancient microscopic life on the surface of Mars.