Stromatolites, Thrombolites and the World's Oldest Life Forms

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Hamelin pool stromatolites in Shark's Bay, West Australia

Stromatolites are stony structures built 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]

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.

Websites and Resources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase; Encyclopedia of Life; Smithsonian Oceans Portal ; Monterey Bay Aquarium ; MarineBio; Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) ; International Coral Reef Initiative ; Coral Reef Alliance ; Global Coral reef Alliance ; Global Coral Reef Monitoring Network

Oldest Stromatolites — 3.5 Billion Years Old

Hamelin pool stromatolites

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

In March 2006, a team from Tokyo Institute of Technology reported in the science journal Nature that it had found evidence of the earliest known life — methane trapped in rock created 3.5 billion years ago, 700 million years old than any previously discovered evidence of life, The rock was found in a 3.5-billion-year-old stratum in the Pilhara region of western Australia. The methane contained carbon 12 — a kind of carbon associated with life. It was likely created by bacteria that lived in hot water near the bottom of the sea.

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

Thrombolites — 1 Billion-Year-Old Life Forms

Thrombolites are kind of similar to stromatolites but not quite 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.

Cambrian-era thrombolite from Virgia

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

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 the charismatic science presenter and University of Manchester’s rock star of particle physics, 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.

Lake Clifton thrombolites

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.

Steroids May Have Helped the First Complex Life-Forms Evolve 1.6-Million Years Ago

Steroids discovered in 1.6 billion-year-old rock may help scientists solve a long-standing mystery about the evolution of single-celled life. Live Science reported: These compounds are produced by eukaryotic organisms, which are defined by having cells with nuclei and interior organelles bound by membranes. Modern eukaryotes include plants, fungi and animals. In contrast, prokaryotes — bacteria and archaea — lack these features. Based on molecular data, researchers know that single-celled eukaryotes first evolved at least 2 billion years ago, but there is very little fossil record of their earliest days. Particularly perplexing is that the steroids the eukaryotes produce as part of their membranes don't show up in the fossil record until about 800 million years ago. The last common ancestor of modern eukaryotes, including today's humans, lived some 1.2 billion years ago and must have produced these steroids, yielding confusion about why they didn't show up in ancient rocks. [Source: Stephanie Pappas, Live Science, June 8, 2023]

Now, researchers have discovered that they were looking for the wrong thing. Instead of searching for modern-looking steroid compounds, they discovered precursors from earlier steps in the microbes' metabolism. The team published their results June 7, 2023 in the journal Nature. "It is like walking past something obvious every day but not 'seeing' it," study first author Jochen Brocks, a professor in the Research School of Earth Sciences at Australian National University, told Live Science. "But once you know what it looks like, you see it suddenly everywhere." Once the researchers figured out which molecules to look for, they found them all over sedimentary rocks from between 1 billion and 1.6 billion years ago. That changes the picture of what researchers believed about eukaryotes' original abundance, Brocks said. "We previously thought eukaryotes were either very low in abundance or restricted to marginal environments where we can't find the molecular fossils," he said. "It now seems that more primordial forms could be quite abundant even in open marine habitat."

The compounds were initially found in rocks that formed at the bottom of the ancient ocean, which are now exposed on land in Australia's Northern Territory. When the researchers expanded their hunt to billion-year-old rocks globally, though, they found traces of steroids n ancient waterways from all around the world, including in West Africa, Scandinavia and China. The oldest samples date back 1.64 billion years; scientists have yet to find older rocks that are preserved well enough for analysis. There is also a gap in the record from between 1 billion and 800 million years ago, Brocks said, because few marine rocks from that time period still exist. That period is right at the cusp of modern eukaryotes' emergence, though, he said, so it's important to fill in those gaps.

The new study is a "significant step" forward in filling in the missing data around early eukaryotes, said Laura Katz, a biologist at Smith College."This paper is helping us understand these early eukaryotes and what early eukaryotes might have looked like," Katz said.

These organisms evolved in a very different environment than today's, Andrew Roger, a molecular biologist at Dalhousie University in Canada, told Live Science. Earth's atmosphere did not contain significant levels of oxygen until 2.4 billion years ago and didn't reach modern oxygen levels until 650 million years ago, Roger said. Oxygen levels in the atmosphere may have played a role in the timing of eukaryote evolution, given that most eukaryotes use oxygen in their metabolism, he said. It's even possible that newly evolved steroids enabled these early eukaryotes to move into new, oxygen-rich environments, Katz said.

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); 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 May 2023

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