What is the difference between microbialites and stromatolites?

Microbialites vs. Stromatolites: What’s the Difference?

When exploring ancient rocks or modern microbial ecosystems, you might come across the terms microbialite and stromatolite. While often used interchangeably, they aren’t quite the same thing.

Microbialite is the broader term, introduced in 1987 to describe any benthic deposit formed by the activity of microorganisms—mainly cyanobacteria and other microbes that trap sediment and precipitate minerals. These structures can take many forms: mound-like, clotted, or even branching, and they thrive in various aquatic environments, from salty lagoons to freshwater lakes.

Stromatolites, on the other hand, are a specific type of microbialite. What sets them apart is their distinct layered (or laminated) structure. These layers are built over time as microbes grow upward toward sunlight, leaving behind mineralized traces that stack like pages in a book. Stromatolites are some of the oldest evidence of life on Earth, with fossil records dating back over 3.5 billion years.

So, think of it this way: all stromatolites are microbialites, but not all microbialites are stromatolites. It’s a subtle distinction, but an important one for geologists and microbiologists studying early life and Earth’s ancient environments.

Today, living stromatolites can still be found in a few rare places—like Shark Bay in Australia or Laguna Bacab in Mexico—offering a window into the world’s earliest ecosystems. Meanwhile, other microbialites without clear layering remind us that microbial life expresses itself in diverse, often overlooked ways.