We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

What is a Stromatolite?

Mary McMahon
Updated: May 21, 2024

A stromatolite is an accreted mass of microorganisms which have grown so closely together that they form a mat. Stromatolites typically form in layers, creating a characteristic stratified look, and they are a topic of intense interest among geologists. Until the 20th century, the only evidence of stromatolites was in fossil form, and scientists presumed that these unique biofilms were extinct. However, in Shark Bay, Australia, a colony of living stromatolites was discovered, rocking the scientific world.

Typically, the microorganisms in a stromatolite are cyanobacteria, also known as blue-green algae. Living in the form of a colony is highly advantageous to these organisms, and numerous examples of microorganisms living in similar colonies can be found all over the world. A single stromatolite can take thousands of years to form, layer by layer, and it may appear in a variety of shapes; many stromatolites look like columns, but they can also form in discs, pyramids, and rings like giant misshapen donuts.

Cyanobacteria thrive where other organisms cannot survive, and some scientists believe that cyanobacteria and stromatolites are probably responsible for the modern survivable atmosphere. These organisms generate energy by using carbon dioxide and sunlight, and the byproducts are oxygen and calcium carbonate, also known as lime. The presence of huge amounts of stromatolites on Earth probably helped fill the atmosphere with oxygen, while the generation of lime ensured that they would be fossilized for people to look at in the future.

Modern living stromatolite colonies are typically found in areas with highly saline and very warm water, mimicking the conditions which stromatolites survived in during the Precambrian era. These mats of bacteria are very fragile, which may explain why the modern colonies have been found in remote areas, far from the reach of humans and grazing animals which could damage them. The Shark Bay colony has actually been designated a World Heritage Site, recognizing its uniqueness.

In fossilized form, a stromatolite has distinctive flaky layers of material, which often form in hills and hummocks. It is also common to find deposits of various minerals between the layers, providing clues to when they formed and what conditions were like. Many fossilized stromatolites are quite colorful, with bands of rich color between more dully colored layers, and they are popular collector's items.

All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a All The Science researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By anon89153 — On Jun 08, 2010

what are they made of?

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

Learn more
All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.

All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.