Are stromatolites and cyanobacteria the same?

Stromatolites and Cyanobacteria: What’s the Difference?

While stromatolites and cyanobacteria are closely linked, they are not the same thing. Think of it this way: cyanobacteria are the living organisms, while stromatolites are the rock-like structures they leave behind over time.

Cyanobacteria are among the oldest known forms of life on Earth. These tiny, single-celled microbes thrive in shallow aquatic environments and can photosynthesize, producing oxygen as a byproduct. Often called blue-green algae (though they’re not actually algae), they played a crucial role in shaping our planet’s early atmosphere by helping to increase oxygen levels billions of years ago. Over time, as colonies of cyanobacteria grow, they trap and bind sediments in layered formations. These layers, mineralized over centuries, form solid structures known as stromatolites. These layered rocks serve as fossilized records of ancient microbial life. In fact, some of the oldest stromatolites date back more than 3.5 billion years, making them some of the earliest evidence of life on Earth. Today, living stromatolites can still be found in a few places around the world—most notably in Shark Bay, Australia, and some isolated saline lakes. These rare modern examples give scientists a glimpse into the conditions of early Earth. So, while cyanobacteria are the living, photosynthesizing architects, stromatolites are the stone “monuments” they build. One is biology; the other is geology shaped by biology. Together, they tell a story that spans billions of years—one of survival, evolution, and the quiet, persistent power of microscopic life.