Living Fossils

Located in Hamelin’s Pool, a shallow area of Shark Bay in Western Australia, these odd formations aren’t rocks—they’re stromatolites, and they were built over millennia by single-celled cyanobacteria (also known as blue-green algae). 4,000 to 6,000 years ago, a huge bank of seagrass began to block the tidal flow into Hamelin’s Pool, which meant that the water became twice as salty as the open ocean. Animals like snails and chitons that would usually feed on the algae couldn’t survive, so the blue-green algae began to flourish. Gathered in colonies, they trapped sediment with their sticky surface coatings. This sediment reacted with calcium carbonate in the water and formed limestone, essentially creating a living fossil—this limestone is alive, its top surface layer teeming with active cyanobacteria. The limestone builds up slowly at a rate of about 1mm per year. The stromatolites in Shark Bay are estimated to be between 3,000 and 2,000 years old, but they’re similar to life forms in Precambrian times, 3.5 billion years ago, at the dawn of complex organisms. There are over 50 kinds of cyanobacteria in Shark Bay, and one is thought to have descended from an organism that lived nearly 2 million years ago, making it a part of one of the longest biological lineages.

(Image Credit: 1, 2)

The Archean World, Peter Sawyer, The Smithsonian Institution

In the Archean, life is at its purest. No courtship, no conflict, no sleep, no song, no fear, no lust—just organisms, simplified to abstraction, thriving in poison, water, and ash. Life is not a substance, but a process: consume and continue.

Thermophiliacs feast on hot spring chemicals, relishing the heavy stink of sulphur, and kaleidoscope the steaming pool’s edges. Elsewhere, stromatolites, shallow-water plateaus of sediment and biofilm, learn photosynthesis, change the atmosphere, and terraform the dawn planet. 

The microbes are oblivious to anything outside of their own homeostasis, yet assemble into communities, unknowingly nestling cell walls against each other. Millions of lives surround each bacteria, but they only know their own, like a man running through the streets of Prague, bumping elbows with a thousand other lives—each rich with hope and love and loss—but thinking only of catching the 207 bus on time.

The species that evaded extinction

17:28 13 September 2011

Colin Barras, biomedical and environment news editor

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Stromatolites have been hanging around for ages (Image:Roger Garwood & Trish Ainslie/CORBIS)

It is five years since Richard Fortey retired from his post as senior palaeontologist at London’s Natural History Museum. Yet that has hardly curbed his academic output or the enthusiasm that drove him to study fossils for more than half a century. If anything, he is rapidly cementing his position as one of his field’s great survivors.

Fortey’s latest book is all about survivors too. Life has notched up something like 3.8 billion years on Earth, and it has been a rough ride. The average mammalian species, for instance, rarely makes it much beyond its millionth birthday before evolution ushers it out of existence by churning out a replacement species that’s an even better fit to its particular environment. Even species who survive this never-ending competition are likely to be snuffed out during a rare mass extinction event.

But the fossil record suggests that every so often evolution hits the jackpot: an organism so impeccably and robustly suited to its environment that further modification is apparently unnecessary. These ancient survivors count their time on Earth in the tens or hundreds of millions of years, and seem able to endure the bleakest of mass extinctions. Darwin had a name for them:living fossils. That peculiarly oxymoronic moniker, too, has survived - for around 150 years.

In Survivors, we are presented with some very long life histories. Take the stromatolites, unassuming microbial mounds found today in a few inhospitable places including Shark bay, a World Heritage area in western Australia. The layered mounds are virtually indistinguishable from fossils found in rocks elsewhere in western Australia - formed 3.45 billion years ago, when life had barely begun to secure a toehold on Earth. Such permanence is remarkable in anyone’s book.

Unfortunately, this longevity is rarely accompanied by beauty: these most ancient of survivors are often lacking in looks. Even Fortey confesses to momentary disappointment when, having travelled from the UK to Australia, he finally sees a living stromatolite.

Other species he encounters are similarly underwhelming in appearance. When he visits Hong Kong it is not in pursuit of some exquisite wild bird, but rather to plod through mudflats digging for worms and shells, including the brachiopod Lingula. There are many intricately whorled shellfish in this world, but as one of the few full-colour pictures in the book confirms, Lingula isn’t one of them. It looks a little like a badly bruised human tongue, and has looked that way for around 500 million years - long before such a thing as a human tongue appeared on Earth.

Perhaps it is because the most durable of survivors are so unimpressive in appearance that Fortey buries them in the middle of the book. We begin and end with far more charismatic - and younger - survivors, including lungfish similar to those found in 220-million-year-old rocks, and horseshoe crabs that have changed barely a jot in 450 million years. The latter appear on the front cover (perhaps inevitably, given that they are the closest living relatives to the trilobites Fortey spent many years studying). Horseshoe crabs are noteworthy for their blue blood - which seems only appropriate for an organism whose ancient looks make it as deserving of regal status as any in the animal kingdom.

This meander into and out of deep time - with leaps between unrelated branches of the tree of life - gives the book a delightfully rambling feel. It’s as if Fortey, free in his retirement to do as he pleases, has grabbed the opportunity to journey across time and taxonomy in a way that no academic tome on evolution would dare. Along the way he indulges in many fascinating asides, drawing on a career’s worth of anecdotes to keep us entertained.

Fortey’s curiosity to explore is undiminished. Seeing evolution’s survivors rarely satisfies him: wherever possible he is keen to touch, taste, hear and smell them too. (Horseshoe crab eggs taste so strongly fishy that they cannot be recommended, he notes.)

The innocent fun that his field can provide is evident in his accounts. One particularly important fossil outcrop he visits in Newfoundland can be explored only if visitors remove their shoes. Like children queuing for a turn on an inflatable castle at a village fete, Fortey and his guides obediently shed their footwear. For a palaeontologist, life doesn’t get much better than a sunny day in such surroundings, he says.

The abiding mystery of the book - one that even Fortey’s many years in palaeontology can provide no answer for - is quite what singles out an organism as a survivor-in-waiting. Conspicuous by its absence, too, is any suggestion that our own species might make the grade. In fact, Fortey’s repeated concern is that 100 million years or more of almost unchanged existence might not be enough to guarantee an ancient survivor’s passage even to the next century. The coiled nautilus made it through the extinction that wiped out the dinosaurs, but might not outlive a tourist industry that prizes its pearly shells.

Enduring survivors are likely to have the last laugh, though. Fortey’s epilogue on cockroaches, virtually unchanged for 300 million years and famously likely to be the sole survivors of a nuclear apocalypse, provides an unsettling reminder of our own species’ surprising fragility.

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Survivors: The animals and plants that time has left behind 
By Richard Fortey 
Published by: Harper Press 
Price: £25

Scientists Solve Disappearance of Stromatolites Mystery

The widespread disappearance of stromatolites, the earliest visible manifestation of life on Earth, may have been driven by single-celled organisms called foraminifera.

The findings, by scientists at Woods Hole Oceanographic Institution (WHOI); Massachusetts Institute of Technology; the Univ. of Connecticut; Harvard Medical School; and Beth Israel Deaconess Medical Center, were published online this week in the Proceedings of the National Academy of Sciences.

Read more:


They’re Microbial Condominiums

Image FE0156 (Stromatolites at twilight, Western Australia)

Image FE0160 (Stromatolites and moon, Western Australia)

Image FE0157 (Stromatolites at dawn, Western Australia)

Stromatolites. These are mineralized microbial communities, formed from blue-green algae (also called cyanobacteria). Over the last 4000 years, algae growing in this area have trapped detritus and sediment, forming large, living rafts known as microbial mats. The secretion of calcium carbonate by the algae has caused the mats to mineralize, forming the rock-like structures seen here. The stromatolites are known as living fossils, because the process of mat formation and mineralization continues today. They are a major constituent of the fossil record for about the first 3.5 billion years of life on earth. Modern stromatolites are mostly found in hypersaline lakes and marine lagoons where extreme conditions due to high saline levels exclude animal grazing. One such location is Hamelin Pool Marine Nature Reserve, Shark Bay in Western Australia where excellent specimens are observed today.

© Frans Lanting / MINT Images / Science Source


Whoever thought pond scum could be so interesting?

Stromatolites are microbial colonies that can reach relatively large sizes. They can be observed today in places like Shark Bay in Western Australia, and are much the same in appearance throughout the fossil record. Stroms have been found in rocks as old as 3.5 billion years old and are thus considered to be one of the oldest know forms of life on Earth. Stromatolites grow extremely slowly and thus have had to become extremophiles; living in hypersaline environments to avoid being grazed upon.

I bloody love stromatolites.

If you’re not aware of what a stromatolite is, check out Shark Bay. This site is also pretty good.

Stromatolites are cyanobacteria that thrive in warm, shallow, highly saline water and respire by producing oxygen (which 2-3 billion years ago converted the Earth’s atmosphere from a reduced one to an oxidised one) and precipitate calcium carbonate to make those rocky structures you can see in the Shark Bay link. Stromatolites grow very slowly, and despite both their growth rate and their highly specific living environment, they have managed to survive every catastrophe and extinction the planet’s thrown at life so far.

In my picture from the Oxford Pitt Rivers museum, you can clearly see the secreted layers as the stromatolite grows.

They are the oldest living things on earth, which is bloody cool in itself, and they provided us with the oxygen necessary for our particular form of life. We really owe our existence to them.

Stromatolites by mark i geo on Flickr.

Stromatolites are structures formed by cyanobacteria. As cyanobateria go through chemical routines, the cyanobacteria became very slightly tacky, and that tackiness trapped microparticles of dust and sand, which became bound together to form weird but solid structures through many, many years 

Source: “A short history of nearly everything” by Bill Bryson.


Steve Brooks of Steve Brooks Photography captured this amazing array of Thrombolites in Lake Clifton on the morning of 25 January, 2014. Lake Clifton is about 115km south of Perth, Western Australia.

Thrombolites are microbial rock-like formations; when the microbes photosynthesise they precipitate calcium carbonate, which forms the dome-like thrombolites. Thrombolites are very similar to stromatolites, which are the earliest fossils and were formed by microbes around 3.5 billion years ago. Stromatolites and thrombolites differ in their formation: stromatolites form in layers built up on top of each other while thrombolites form by a clotting process, spread unevenly over time.

Brooks used a Canon 6D with a 24-105mm lens; ISO 100, f/10 and 20 second exposure.


Stromatolites are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria. Stromatolites provide some of the most ancient records of life on Earth by fossil remains which date back more than 3.5 billion years ago. 

(Image: Pre-Cambrian stromatolites in the Siyeh FormationGlacier National Park)