Stromatolites

Living stromatolites at Hamelin Pool in Shark Bay are formed as photosynthetic microbes trap and bind sediment, slowly building mounds and columns layer by layer. They are close analogues to fossil stromatolites that were common in the Archaean and Proterozoic oceans, when few larger organisms existed to graze them down. Each layer represents a response to light, nutrients, and chemistry. Over immense spans of time those responses became stone. In one object we can see how fragile surface life and solid crust are part of a single process.

When scientists look for life on Mars or on exoplanets, they often imagine something like stromatolites appearing first. Simple microbes, finding energy gradients and water, leave patient traces that outlast continents. These structures remind us that complex life rests on an unimaginably long apprenticeship of cells learning how to use light. The stromatolites are a bridge between the earliest life on Earth and the possibility of life elsewhere. They show that life can begin simply, persist for billions of years, and leave traces that survive long after the organisms themselves are gone.