Stromatolite-building bacteria once ruled the Earth, then changed its climate so much they nearly became extinct. Michael Slezak visits the world’s largest surviving colony in Hamelin pool, Western Australia

The natural wonder that holds the key to the origins of life – and warns of its destruction

Just shy of the westernmost tip of the Australian continent lies a pool that provides an unparalleled window into the origins of life on Earth. In its warm, briny waters a biological process takes place that began just as the continents were starting to form.

It is this very process that made the abundance of life on the planet possible and studying it today promises insights into how life began as well as what the Earth was like 3.7bn years ago.

It is also a cautionary tale about an organism that dominated the Earth and transformed its atmosphere – then found itself unable to live with the result.

Hamelin pool contains the world’s largest collection of active stromatolites – stony mounds of sand and calcium carbonate stuck together with a kind of biological glue, which emerge from the water as the tide goes out.

The bacteria that build these stony mounds transformed the planet from a scorching ball of carbon dioxide into the temperate, oxygen-rich world we enjoy today. The mounds they built around the world reveal that they began the process at least 3.7bn years ago. By about 1.25bn years ago, the bacteria that formed them were the world’s dominant lifeform.

Facebook Twitter Pinterest Stromatolites at Hamelin pool, which emerge from the water as the tide goes out. Photograph: Michael Slezak/The Guardian

These cyanobacteria belong to the family known as blue-green algae – a misnomer since they are not an algae at all. They were among the first organisms to collect their energy from the sun using photosynthesis – breathing in carbon dioxide and breathing out oxygen.

According to current scientific theories, these bacteria – or their ancestors – then donated the genes that let them photosynthesise to other organisms (in a process known as “lateral gene transfer”). Those other organisms then evolved into the plants we see on land and the seafloor.

In doing so, the stromatolite-forming bacteria sowed the seeds of their own destruction. Though they thrived in hellish environments like those on early Earth, they were unsuited to the paradise they created and disappeared. In a process that is hard not to compare with what humans are doing now; they changed the climate so dramatically they were no longer able to survive.

Facebook Twitter Pinterest Bush Heritage ecologist Ben Parkhurst holding a native mouse. Photograph: Michael Slezak/The Guardian

Or at least that was what scientists thought until 1956, when an oil company surveying Hamelin pool found active bacteria. Since then they have been found in a handful of places around the world but Hamelin pool is by far the most important. In its waters lie many more active stromatolites than any other location – roughly 100m of the slimy mounds, each growing by about 1mm a year.

“It’s the largest collection of stromatolites in the world and the most diverse,” says Erica Suosaari, a geologist and stromatolite expert from Bush Heritage Australia. “It’s the only place in the world that provides a window to early life in Earth on such a scale.”

Suosaari says the bacteria building the stromatolites at Hamelin pool are the same as those that were active 3.7bn years ago. “It’s as if a single species – like humans – lived for that long,” she says. “Eighty per cent of the history of life was stromatolites – for that time, stromatolites were king.”

In the most general terms, it is the extreme nature of the pool – the high salinity, the large tides and the enormous swings in temperature that emulate aspects of early Earth – that makes it possible for these extremophiles to grow.

But exactly why they thrive here and very few other places – and why they grow in some parts of Hamelin pool but not others – is a mystery that Suosaari is slowly cracking open.



The answers to those questions will not only tell us about the beginning of life on Earth but reveal what the planet was like 3.7bn years ago. If we know what stromatolites need to become abundant, then we know what conditions must have existed when they ruled the world.



Facebook Twitter Pinterest Erica Suosaari, a geologist and stromatolite expert from Bush Heritage Australia, says the bacteria building the stromatolites at Hamelin pool are the same as those that were active 3.7bn years ago. Photograph: Michael Slezak/The Guardian

Suosaari also collaborates with Nasa. Stromatolites are such a lasting and extensive signature of life on Earth that they might give clues about how to find life on other planets, too.

She has some theories about what might determine stromatolite success. She thinks it’s to do with the existence of groundwater below the pool and how it changes the chemistry of the surface water. She’s busy measuring surface and groundwater at various locations around Hamelin pool to search for correlations.

“So far it’s just speculation,” she says – but she can’t help revealing her excitement at the possibility that she is right.

Protecting the pool

Hamelin pool has the highest level of environmental protection available. Unesco has listed almost 5m hectares of marine and terrestrial environment in Shark Bay as a world heritage area.

But, until last year, Hamelin pool was nestled up against a grazing station, inhabited by thousands of sheep and goats. The world heritage area only extended to a little beyond the high-tide mark. To the west of the pool, land was included in the heritage-listed area but, to the south and east, stock were grazed on the land.

It’s the only place in the world that provides a window to early life in Earth on such a scale Erica Suosaari

On the drive to Hamelin pool, you can see the damage the farming was causing. The removal of surface vegetation meant gullies had formed. These could have allowed fresh rainwater and sediment to wash into the pool, altering its delicate balance.

And with many plants being eaten by the farm stock, the way groundwater was collected below the land was likely to have been changed. If Suosaari is right about the importance of groundwater to stromatolites, that could have been a problem.

Last year Bush Heritage Australia bought up 200,000 hectares of land and set it up as a conservation reserve. In doing so, Suosaari says, it has essentially extended the world heritage area,

Not just ancient life

Besides protecting Hamelin pool’s shoreline, the new conservation reserve completes a connected corridor of nature reserves from Shark Bay, through Toolonga nature reserve and crown land over to Bush Heritage Australia’s Eurardy reserve and then Kalbarri national park – a total span of more than 200km.

Facebook Twitter Pinterest Ecologist Ben Parkhurst has been leading a survey of the birds, small rodents, marsupials and reptiles on the station. Photograph: Michael Slezak/The Guardian

Although Suosaari is most excited about the protection of the stromatolites, back on dry land there is similarly important conservation work going on.



The Bush Heritage ecologist Ben Parkhurst has been leading a survey of the animals that live on the station – the birds, small rodents, marsupials and reptiles.

Each day – morning and night – Parkhurst and his team drive around the enormous site setting drop traps, studying their contents and releasing the various critters they find. Their work is complemented by that of a team from the Western Australian Museum who are studying the insects that live here.

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Together they are trying to build a complete picture of the area’s ecosystem, and prepare a baseline, so they can measure how effective their conservation measures – such as cat, rabbit and fox eradication – are.

Besides the snakes, native mice, small marsupials and various goannas the team find each day, there is one species that Parkhurst is particularly keen to understand and protect.

The Hamelin skink is a lizard that only exists in this area, making it extremely vulnerable to extinction. Its range is just 150 sq km, leaving its fate completely dependent on what happens on just two properties: the newly protected Hamelin station and the neighbouring Coburn station.

Exactly what species live in the area is still unknown. Bush Heritage estimates there are 240 species of bird and 820 plants, alongside a completely unknown number of reptiles.

Facebook Twitter Pinterest Prints left by a marsupial on Hamelin reserve. Photograph: Michael Slezak/The Guardian

Climate change

Bush Heritage Australia’s conservation efforts will give the active stromatolites in Hamelin pool, as well as the neighbouring flora and fauna, a great chance at surviving. But the cautionary tale of the stromatolite-forming bacterias dominating the Earth, then transforming it such an extent that they were unable to continue forming their mounds, is one that has not been heeded by humans.

As sea levels rise – which they will inevitably do as the climate warms – the shelf that isolates Hamelin pool from the ocean is likely to be flooded. Inundated by colder, less salty water, the pool will lose its extreme nature.

The climate change humans are causing may just be the final nail in the coffin for these trailblazing bacteria, wiping out the stromatolite-builders at Hamelin pool.

Guardian Australia travelled to Hamelin pool as a guest of Bush Heritage Australia