Stromatolites — World's Oldest Life Forms — What and Where They Are | Sea Life, Islands and Oceania

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STROMATOLITES — WORLD'S OLDEST LIFE FORMS

Hamelin pool stromatolites in Shark's Bay, West Australia

The earliest direct known life on Earth are stromatolite fossils found in 3.48-billion-year-old geyserite unearthed in the Dresser Formation of the Pilbara Craton of Western Australia. Microfossils of various sorts of microorganisms have been found in 3.4-billion-year-old rocks, including 3.465-billion-year-old Apex chert rocks from the Pilbara craton region, and in 3.42-million-year-old hydrothermal vent precipitates from Barberton, South Africa.

Stromatolites are layered rock formations created by colonies of microscopic algae-like bacteria. Under some conditions, as sediment forms in shallow water, bacteria grows over them and binds with particles in the sediment. Over time the sediments attach to the sticky surfaces of bacteria and minerals dissolved in the waters turn into solid layers that bond with and build upon other similar layers until they become mounds. These mounds formed the world's first reefs and were the Earth's first life forms. [Source: BBC]

Unlike many modern reefs that are made by corals, the builders of the first reef-like structures were cyanobacteria — microbes that grow in slimy sheets, forming layered mounds described above. When fossilized, the layered microbial structures are known as stromatolites. Some date as far back as 3.5 billion years ago, providing some of the earliest convincing traces of any kind of life on Earth. [Source: Maya Wei-Haas, National Geographic Science News, July 29, 2021]

In a more technical definition, stromatolites, or stromatoliths are layered sedimentary formations that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). These microorganisms produce adhesive compounds that cement sand and other rocky materials to form mineral "microbial mats". In turn, these mats build up layer by layer, growing gradually over time. A stromatolite may grow to a meter or more. Although they are rare today, fossilized stromatolites provide records of ancient life on Earth. [Source: Wikipedia]

Marian McGuinness of the BBC wrote: Stromatolites are living fossils and the oldest living life forms on our planet. The name derives from the Greek, stroma, meaning “mattress”, and lithos, meaning “rock”. Stromatolite literally means “layered rock”. The existence of these ancient rocks extends three-quarters of the way back to the origins of the Solar System....Their empire-building brought with it their most important role in Earth’s history. They breathed. Using the sun to harness energy, they produced and built up the oxygen content of the Earth’s atmosphere to about 20 percent, giving the kiss of life to all that was to evolve. [Source: Marian McGuinness, BBC, January 19, 2021]

Websites and Resources: ; Wikipedia article on Stromatolites Wikipedia Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures

Where You Can See Stromatolites

You can find stromatolites in a few places, both living and fossilized. Living stromatolites are rare and typically found in hypersaline (very salty) environments like Shark Bay, Western Australia, and the Bahamas, which prevent most animals from grazing on them. They also exist in other extreme conditions, such as the hot springs of Yellowstone National Park. Fossilized stromatolites are more widespread and can be found in ancient rock formations worldwide, such as the ~3.5 billion-year-old fossils in the Dresser Formation of the Pilbara region, Western Australia.

Hamelin pool stromatolites

Living stromatolites
Shark Bay, Western Australia: Hamelin Pool Marine Nature Reserve is one of the most famous and well-developed modern stromatolite sites.
The Bahamas is another major area for living marine stromatolites.
Puna de Atacama in Argentina
Yellowstone National Park, U.S. has some in alkaline hot springs.
México in Bacalar and Cuatro Ciénegas.

Fossilized stromatolites
Pilbara region, Western Australia contains some of the oldest fossils, dating back about 3.5 billion years.
Capitol Reef National Park, Utah has large fossilized stromatolites.
Glacier National Park, Montana contains stromatolite fossils in ancient rock.
Wyoming has places where stromatolite fossils formed nearly 2 billion years ago.

Oldest Stromatolites — 3.5 Billion Years Old

Limestone traces of 3.5 billion year old stromatolite have been found at a place in the Pilbara region of Western Australia ironically called the North Pole. These organisms lived at a time when the earth's atmosphere was composed mostly of carbon dioxide, or in other words an atmosphere more similar to the one on Mars than the one on earth today. Through photosynthesis, stromatolite and other plants created the oxygen we now breath today. Stromatolite, almost exactly the same as their 3.5 billion year old ancestors, can also still be found in Western Australia.

The Pilbara of northwestern Australia exposes some of the oldest rocks on Earth — over 3.6 billion years old. The oldest rocks at Pilbara are so old that they contain no fossils within its structure. The oldest fossils are from stromatolites. They are considered the fossilised evidence of the Earth's oldest life forms.

In 1980, 3.45-billion-year-old fossil stromatolites were found near Marble Bar in the Pilbara. These microbial cyanobacteria communities first existed when conditions on Earth could not support any other form of life and built bulbous reef-like structures as they released oxygen through photosynthesis.

Amazingly, just south of the Pilbara at Hamlin Pool near Shark Bay, the world's most extensive living stromatolites system is still thriving, even fizzing, as it produces oxygen in the hypersaline bay. This is one of just two places on Earth where living marine stromatolites exist. See Below

Ancient Versus Modern Stromatolites

Cross section of a stromatolite fossil from Strelley Pool Chert (SPC) Pilbara Craton in Western Australia, dated to 3.6 to 3.2 billion years ago: Stromatolites are formed over the years by mats of mostly of cynobacteria microorganisms between one and 10 millimeters thick found in shallow, mainly marine waters; The microorganisms precipitate mineral particles, which makes the mat thicken, but only the upper part survives; Most stromatolites display characteristically layered structures, with only the layers are visible to the naked eye

Ancient giant stromatolites were widespread during the Precambrian era of Earth, which spanned from around 4.6 billion to 541 million years ago. Now, they are sparsely distributed around the world. According to the nonprofit conservation organization Bush Heritage Australia, the most well-developed areas are in the Bahamas and the Shark Bay area in Western Australia. [Source: Taylor Nicioli, CNN, December 16, 2023]

Brian Hynek, a professor in the Department of Geological Sciences at the University of Colorado Boulder, said that modern stromatolites are relatively small. Ancient stromatolites, on the other hand, grew to 20 feet (6 meters) tall and 16 to 22 feet (5 to 7 meters) wide.

Unlike modern stromatolites, ancient stromatolites grew during a time when the atmosphere lacked oxygen. In these conditions, their microbes used anoxygenic photosynthesis to convert light energy into compounds that support living cells. This process does not require oxygen.

Living stromatolites today are covered with algae-like bacteria which is exposed during the day. At night the microorganisms fold over, trapping the calcium in the water. Layers of the calcium deposits created the stromatolite formations. Stromatolites can be formed a simple combination of sediment precipitation, diffusion and random effects. Organism may not play a essential role.

Living Stromatolites at Hamlin Pool in Western Australia

Hamlin Pool (32 kilometers, 20 miles off the Northwest Coastal Highway) is a marine park with world's most famous colonies of stromatolites. They grow well because of the water’s clarity and high salt content. It was long thought that was the last remaining colonies of stromatolites were found only in Western Australia but in recent years other have been found in the Caribbean.

According to UNESCO: stromatolites are colonies of microbial mats that form hard, dome-shaped deposits which are said to be the oldest life forms on earth. Hypersaline Hamelin Pool contains the most diverse and abundant examples of stromatolites in the world. Analogous structures dominated marine ecosystems on Earth for more than 3 billion years ago. The stromatolites of Hamelin Pool were the first modern, living examples to be recognised that have a morphological diversity and abundance comparable to those that inhabited Proterozoic seas. As such, they are one of the world’s best examples of a living analogue for the study of the nature and evolution of the earth’s biosphere up until the early Cambrian. [Source: UNESCO]

Marian McGuinness of BBC wrote: We can witness how the world looked at the dawn of time Living stromatolites are found in only a few salty lagoons or bays on Earth. Western Australia is internationally significant for its variety of stromatolite sites, both living and fossilised. Fossils of the earliest known stromatolites, about 3.5 billion years old, are found about 1,000 kilometers north, near Marble Bar in the Pilbara region. With Earth an estimated 4.5 billion years old, it’s staggering to realise we can witness how the world looked at the dawn of time when the continents were forming. Before plants. Before dinosaurs. Before humans. [Source: Marian McGuinness, BBC, January 19, 2021]

Visiting Living Stromatolites at Lake Thetis in Western Australia

Marian McGuinness of BBC wrote: I was almost at Cervantes, the rock lobster capital of the coast on the northern edge of Nambung National Park. A couple of kilometres down a dirt road, I reached Lake Thetis, the home of the stromatolites. Lake Thetis was small, shallow and triangular. The bush track wound through thick-leaved, blue-petalled fanflower, seed-headed rushes and rashes of red-beaded samphire. Every now and then, the local kangaroos popped their heads up to check us out. [Source: Marian McGuinness, BBC, January 19, 2021]

And then I saw them. There were thousands of pumice-hued stromatolites quasi-camouflaged beneath the ripples, submerged like migrations of ancient turtles holding their breaths under the slightly opaque water. I was awestruck. Blocking out the peripheral surrounds and imagining the sky methane orange from volcanic activity, this is what life looked like at the beginning of time.

Lake Thetis is just more than two meters deep and double the salinity of the sea. The lake became isolated about 4,800 years ago when the sea level fell during the last major glacial epoch. Shorelines receded and coastal dunes trapped the water inland, creating the lake. These stony oxygen givers are estimated to have been growing for about 3,500 years.

A metal walkway braces out over the lake so you can see the stromatolites beneath. On the 1.5 kilometer walk that circumnavigates the lake, it’s look, but don’t touch, as many of the these ancient relics have been damaged by people carelessly walking on them. But there’s another side of the stromatolite family that is present on this stretch of coast. Evolutionary progress around a billion years ago started a slow segue that saw the layered stromatolites disappear as another variation emerged. They were their younger cousins: the thrombolites. See Below

Stromatolites of Argentina's Puna de Atacama

Scientists discovered a previously hidden ecosystem of stromatolites in the lagoons in hypersaline lakes in Argentina's Puna de Atacama that they say could be good examples of the earlier form of life on Earth.These stromatolites are of particular interest because they may resemble the conditions of early Earth and could be analogous to the earliest forms of life on our planet. The Puna de Atacama provides a harsh, high-altitude, and extremely salty environment, offering a unique window into the past. The Stromatolites were formed by microbial mats, primarily composed of cyanobacteria (formerly known as blue-green algae) that trap and bind minerals and sediments, gradually building upwards over time.

Puna de Atacama, in this high-altitude parts of the Atacama desert in Argentina, is one of the driest places on Earth, characterized by salt flats and lagoons. The lagoons within the Puna de Atacama are unique because they contain living stromatolites, offering a modern example of what early Earth environments may have been like. The stromatolites found in this region are thought to be similar to those that existed billions of years ago, providing clues about the earliest forms of life and the conditions they thrived in. Potential for Martian Research:The extreme environment of the Puna de Atacama is also being studied for its potential to inform the search for similar microbial life on Mars, which may have had comparable conditions billions of years ago.

CNN reported: Stromatolites tend to grow in alkaline conditions, but the Puna de Atacama’s system of lagoons are acidic. Also, most stromatolites found today are carbonate rocks (made of limestone), but the ones in Argentina are are mostly composed of the minerals gypsum and halite (rock salt). Hynek said. “These are certainly akin to some of the earliest macrofossils on our planet, and in really a rare type of environment on modern Earth...They are a window into the distant past as to what life might have looked like 3½ billion years ago on our planet.”[Source: Taylor Nicioli, CNN, December 16, 2023]

The Argentina stromatolites are also very large — up to 15 feet (4.5 meters) wide and several feet high, according to a news release from the University of Colorado Boulder. It is unclear why the stromatolites are so large, Hynek said, but he speculated that the inland ecosystem sat undisturbed for a long period of time, which allowed them to grow unimpeded. Hynek spotted the system of lagoons through satellite imagery in April 2022 when he was studying another lagoon in northwestern Argentina that had smaller stromatolites with microbes that use anoxygenic photosynthesis. He and microbiologist Maria Farías, cofounder of Punabio SA Environmental Consulting, presented the findings December 11 at the 2023 meeting of the American Geophysical Union in San Francisco.

“It is spectacular to find structures that could be biogenic (produced by living organisms) at this unusual altitude,” Pieter Visscher, a professor of marine sciences at the University of Connecticut, who has extensively studied stromatolites, told CNN. “A major issue with the discovery, whether biogenic or not, is that these are formed in the presence of oxygen (in the current atmosphere). Until 2.3 billion years ago, there was no oxygen.”

While the stromatolites are in an environment containing oxygen, Hynek said he believes the layers farther down in the rock have little to no access to oxygen and are actively formed by microbes using anoxygenic photosynthesis. This would make the structures similar to the ones found on ancient Earth. “We’re not sure if the microbes are actively participating in their growth (in the newly discovered stromatolites). We think they are. But we haven’t done the experiments yet to try to figure that part out,” said Hynek “There’s a lot of work to be done. We just discovered them and hardly scratched the surface.”

Thrombolites — 1 Billion-Year-Old Life Forms

Cambrian-era thrombolite from Virgia

Thrombolites are kind of similar to stromatolites but not as old — by a couple billion years but still date back to more than a billion years ago. Thrombolites are clotted accretionary structures formed in shallow water by the trapping, binding, and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria. They don’t the have laminae (thin sedimentary rock layers) of stromatolites. The word “Thrombolite” derives from the same root as thrombosis, which means “clot”. Thrombolites are clotted in appearance, whereas stromatolites are layered. [Source: Wikipedia]

Each clot within a thrombolite mound is a separate cyanobacterial colony. The clots are on the scale of millimetres to centimetres and may be interspersed with sand, mud or sparry carbonate. Larger clots make up more than 40 percent of a thrombolite's volume and each clot has a complex internal structure of cells and rimmed lobes. Very little sediment is found within the clots because the main growth method is calcification rather than sediment trapping.

There are two main types of thrombolites: 1) Calcified microbe thrombolites, which contain clots that are dominantly composed of calcified microfossil component and do not have a fixed form or size and sometimes contain trilobite fragments; and 2) coarse agglutinated thrombolites, composed of small openings that trap fine-grained sediments. The latter are also known "thrombolitic-stromatolites" due to the similarity of their composition to that of stromatolites. Thrombolites can be distinguished from stromatolites by their massive size, which is characterized by macroscopic clotted fabric. Stromatolites are similar but consist of layered accretions. Thrombolites appear with random patterns that can be seen by the naked eye, while stromatolites has the texture of built up layers.

Calcified microbe thrombolites occur in sedimentary rocks from the shallow water ocean during the Neoproterozoic Period (1 billion to 538.8 million years ago) and early Palaeozoic Period (541 to 252 million years ago). According to the late Dr Linda Moore from the University of Western Australia and the BBC, stromatolites went into decline at a time where there was an explosion of more advanced marine life. Their ecosystem became challenged as the predator amoeba and other single-celled organisims called foraminifera used their finger-like extensions to engulf stromatolites, turning their fine, layered structures into clumps. To survive, stromatolites needed highly saline water that restricted other competing sea life, whereas thrombolites adapted. They survived and prospered in an environment less salty than the sea, their clotted texture providing a home where tiny fauna could coexist. [Source: Marian McGuinness, BBC, January 19, 2021]

Thrombolites can survive in environments less salty than the sea They are rare today but exist in a few places where groundwater discharge combines with high concentration of nutrients and organic ions, such as shallow seawater, freshwater, and saltwater lakes, and streams. These places include: 1) Laguna Negra, in Catamarca, Argentina; 2) Basin Lakes and Blue Lake, Lake Clifton, Lake Richmond and Lake Thetis in Australia; 3) Flower's Cove, Manito Lake and Pavilion Lake in Canada; 4) Lakes Nuoertu and Huhejaran in China; 5) Kiritimati Atoll in Kiribati; 5) Cuatro Ciénegas and Lake Alchichica in Mexico; 6) Ciocaia in Romania; 7) Lake Van and Salda Lake in Turkey; and 8) Green Lake in the U.S.

Living Thrombolites at Lake Clifton, Australia

Lake Clifton thrombolites

Marian McGuinness of BBC wrote: About an hour’s drive south of Perth, I took the Old Coast Road into the Yalgorup National Park to Lake Clifton, home to the largest lake-dwelling thrombolites in the Southern Hemisphere. When University of Manchester Professor Brian Cox, visited the thrombolites for his documentary series, Wonders of the Universe, his awe for the “weird, rocky blobs in the shallows” inspired many travellers to seek out Lake Clifton, to see “the first life on Earth”. [Source: Marian McGuinness, BBC, January 19, 2021]

With an impressive ancient lineal ancestry, Lake Clifton’s thrombolites are estimated to be a youthful 2,000 years old. Here, too, a boardwalk ventures through the reeds and over the brackish lake, where beneath, the thrombolites can be viewed. With careful watching, you can see tiny strings of oxygen rising to the water’s surface. They are breathing.

To the Noongar people of this region, their Dreamtime story tells the origin of the thrombolites. With the land dry, the Noongars prayed to the sea for the water to become fresh. Their creator left the sea in the form of the serpent, Woggaal Maadjit. She pushed through the sand dunes, creating an inlet. She laid her eggs (the thrombolites) and curled her body to protect them (the sand dunes protecting the lake). The baby serpents from the eggs that hatched carved out rivers, then when dying, they tunnelled underground forming subterranean springs on their way back to the Dreamtime.

These springs provided fresh water for the Noongar people. From a scientific point of view, the microbial thrombolites use sunlight to photosynthesise for energy and to precipitate calcium carbonate (limestone) from the freshwater springs that bubble from the underlying aquifer. Groundwater flow that is low in salinity and nutrients and high in alkalinity is integral to their growth and survival; any alteration challenges their existence.

Stromatolites on Mars?

While no definitive stromatolites have been found on Mars, there is evidence suggesting that ancient Martian shorelines could have hosted them, and scientists are actively searching for them, particularly in places like Jezero Crater. Structures similar to stromatolites have been reported on Mars that could be fossilized evidence of past life, though abiotic (non-biological) processes cannot yet be ruled out. The Perseverance rover is equipped to search for these signs of life and collect samples for potential return to Earth. [Source: Google AI]

If the stromatolites are produced by microbes using anoxygenic photosynthesis, the discovery could provide insight on the possibility of life on ancient Mars, Hynek told CNN. “We’ve identified more than 600 ancient lakes on Mars; there may have even been an ocean. So, it was a lot more Earth-like early on,” he said. Hynek also said the minerals gypsum and halite, found in the stromatolites in Argentina, are also in salt deposits all over Mars. [Source: Taylor Nicioli, CNN, December 16, 2023]

“If Mars ever evolved life through photosynthesis, this is the type of thing we’d be looking for (stromatolites) — and it is the type of thing we’re looking for,” said Hynek, who is also a research associate at the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics. “If we’re going to find any sort of fossils on Mars, this is our best guess as to what they would be, because these are the oldest ones from the Earth rock record.”

Recent discoveries on Mars have included domed, concentric circular formations that resemble stromatolites found on Earth. Evidence from NASA's rovers suggests that parts of ancient Mars had water and were potentially habitable for microbial life. The presence of carbonate deposits in areas like Jezero Crater is significant because these minerals on Earth are known to form hardy structures that can survive for billions of years, including some stromatolites.

Scientists are studying ancient stromatolites on Earth to develop a template for what to look for on Mars, as there are structural elements that can help identify their biological origins, as explained by BBC News. A major challenge is distinguishing between genuine stromatolite fossils and rocks formed by abiotic geological processes.The Perseverance rover's primary objective is to collect rock core samples that future missions could return to Earth for more detailed analysis, which is necessary to confirm if they are truly the remnants of ancient life

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated November 2025