(Inside Science) -- Billions of years ago in a shallow sea in what is now western Australia, microbes grew in layered cones that climbed toward a hazy orange sky. The water they lived in was green with iron; the continent above was black, bare of any life.
The cones likely grew as photosynthetic microbes pushed toward the highest points to soak up light. Yet if the microbes were using sunlight, their methods for gleaning energy were primitive and produced no oxygen. It would be another billion years before living things filled the air with oxygen and turned the sky blue.
Fast forward to the year 1994. The sea was dry, the microbes long dead, but their cityscape remained. In a patch of ground no larger than a living room, geologist and astrobiologist Martin Van Kranendonk could see how tidal movements rippled the seabed 3.4 billion years ago. The three largest cone-shaped structures, known as stromatolites, rose a foot above the surrounding rock.
That fossilized scene is one of a handful of small outcrops in the Pilbara region of Australia that hold the oldest convincing evidence of life on Earth. In 1998, Van Kranendonk returned with a team of researchers. When he approached the area that had been home to a cluster of cone-shaped stromatolites, he saw the three largest ones were gone, deliberately broken off at the base.
The three roundish shapes on this rock are the "stumps" where conical stromatolites were removed.
Martin Van Kranendonk
This image may only be reproduced with this Inside Science article.
"It felt like coming across a rhinoceros whose horn had been sawn off its body," said Van Kranendonk, who is now director of the Australian Center for Astrobiology at the University of New South Wales. "It was really heartbreaking."
The Pilbara fossils are famous around the world for the window they offer onto primeval life. What's less well known is that they are being stolen. The most valuable sites are listed as state geoheritage reserves, so it's illegal to visit or disturb them without permission from the government of Western Australia. But there is no on-the-ground enforcement, and even after the geoheritage reserves were established in 2010, destruction continued.
Now, scientists and Aboriginal Nyamal people are working to protect Pilbara's remaining fossils before they disappear.
Earth's oldest cityscapesScientists first described stromatolite fossils over a century ago, but it wasn't until live stromatolites were discovered in the late 1950s that researchers really understood what they were looking at, said Van Kranendonk.
How Do We Know if a Rock Was Made by Microbes?Identifying fossilized stromatolites can be tricky. One clue is that the layers are wrinkly and irregular, and such surfaces usually aren't created by simple geological processes, said Martin Van Kranendonk, director of the Australian Center for Astrobiology at the University of New South Wales. The story becomes clearer when sediment piles up against a stromatolite, preserving biological and geological processes side by side.
In the case of the oldest Pilbara stromatolites, the clincher came when researchers including Van Kranendonk analyzed the fossils' microscopic structure in 2019. They found a spongelike web of pyrite, a shiny mineral also known as fool's gold. The spongey structure was tiny in scale, with holes as small as a single micron -- about one hundredth the width of a human hair.
When pyrite is created through nonbiological processes, it tends to form large, solid crystals. But pyrite can also precipitate out of the water as a side effect of metabolism by organisms that live without oxygen. This is because many anaerobic bacteria release hydrogen sulfide, which reacts with dissolved iron to form pyrite.
Some types of modern stromatolites that grow in flat sheets in Western Australia's Shark Bay still form pyrite a few centimeters under their surface, where all the oxygen has been used up. When the Pilbara stromatolites were growing, there was virtually no free oxygen anywhere, so it makes sense that their microbes might have caused pyrite to form.
Inside the holes and tunnels of the pyrite sponge, the researchers found something even more exciting: organic material. The organic matter appeared to be the remains of goo that microbes produce to live in and move through.
"We see these twisted ropes and fibers of the organic matter coming in and out of that pyrite. So we know that that mineral had been precipitated around those organic strands," said Van Kranendonk. "The type of organic matter that we found is identical to what's left behind in living stromatolites today."
The sidebar image is an electron microscope view of a stromatolite fossil showing a filament of organic material threading through pyrite.
Image credit: Raphael Baumgartner. From Geology, 47(11), 1039–1043[/size]
Modern stromatolites are built by complex communities of thousands of different types of microbes, most of which are bacteria. The microbes grow in thin layers interspersed with layers of silt and other sediment. The biological activity also changes the seawater's chemistry and causes certain minerals to settle out of the water, entombing the microbes as they grow. It's thought that ancient stromatolites formed the same way.
The combination of falling sediment and precipitating minerals makes stromatolites harden quickly. Only the top layer is soft; the deeper ones are in a sense already fossilized. This is why stromatolites survive so well in the geologic record, said Van Kranendonk.
Stromatolites come in a variety of shapes, including rounded domes, cones, columns and flat sheets. In modern times, they tend to grow in places that are difficult for other life-forms to survive in, said Van Kranendonk. For example, living stromatolites have been found in hot springs in Yellowstone National Park, in a freshwater lake in Antarctica and in the extremely salty waters of Australia's Shark Bay.
In the distant past, stromatolites were probably much more common, since there were no plants, animals or protozoa for them to compete with. Fossil stromatolites have been found at many sites around the world.
The Pilbara region contains several ages and types of stromatolites, as well as additional fossils too small to be seen without a microscope. The oldest site, which contains the best fossils from a layer of rock called the Dresser formation, is thought to be the remnant of a volcanic hot spring where flat, dome-shaped, and conical stromatolites all grew close together. Those stromatolites are 3.5 billion years old, more than 50 times older than the last Tyrannosaurus rex.
There are even older rocks from Greenland that some researchers believe to be stromatolites, but those are more controversial because they have lost much of their fine-scale structure. In contrast, the Pilbara region is preserved in remarkable detail. "Really all that's happened to it is it's sat there for three and a half billion years and been tilted a bit," said Van Kranendonk.
Disappearing FossilsAs early as 1987, less than a decade after publication of the first scientific paper on the oldest group of Pilbara fossils, a report commissioned by the Geological Society of Australia, Western Australia Division, tried to raise the alarm.
"Key stromatolite sites have been looted," the document reads. "Some of these records of life's beginnings are in danger of being lost."
Because the sites are so small and early stromatolite fossils are rare, every piece taken represents a major loss, said Clare Fletcher, a geographer and graduate student who works with Van Kranendonk at the Australian Center for Astrobiology. The first site ever studied, named "Dunlop" for one of its discoverers, was stripped of fossils decades ago, she said.
In those days, it appeared that much of the looting was by scientists themselves, who took fossils for research or for display. In 2010, the Western Australia state government established six Pilbara fossil sites as geoheritage reserves, with a management plan that required people to obtain permits before visiting or collecting. It was thought that researchers would voluntarily respect the regulations and go through the proper channels, and indeed many scientists have been cooperative, said Sarah Martin, a paleontologist who helps manage the sites for the Geological Survey of Western Australia within the Department of Mines, Industry Regulation and Safety. The reserves also ensure that no mining permits are issued on the sites.
Nevertheless, there have been several pieces taken since the reserves were established, including a large slab showing a detailed cross-section of stromatolites that was originally part of the scene where Van Kranendonk found the decapitated cones.
Additionally, legal designations that highlight a site's importance without enforcing on-the-ground protections may backfire, essentially placing a spotlight on vulnerable resources, said Ian Percival, a retired paleontologist formerly with the Geological Survey of New South Wales.
There's no way to know for sure who is taking the specimens, but several people interviewed for this article suspect commercial dealers and members of the public. Pilbara stromatolites appear frequently on eBay and on fossil dealing sites.
Astrobiologists Martin Van Kranendonk and Tara Djokic examine the fossilized remains of an ancient hot spring in the Pilbara region of Australia.
Courtesy of the University of New South Wales. Still image from "Life on Earth -- and Mars?"
Martin said she is not aware of any specimens for sale that were obviously collected illegally, since stromatolites can also be found outside the reserves. However, it is illegal to bring such fossils out of Australia without a permit, and many specimens for sale offer international shipping.
Nevertheless, Heidi Allen, a paleontologist with the Geological Survey of Western Australia, noted that scientists may still be among the culprits. "The people who understand the real value of it are people who understand the science," she said. "I'm not so sure that it's just the regular Joe Blow who wants a piece of this really old stromatolite on his mantelpiece."
Inside Science reached out to eight sellers offering stromatolite fossils attributed to the Pilbara region, but only one replied, saying that their specimens came from an old collection rather than newly collected material.
The value of fossils left in placeAs the earliest clear signs of life on Earth, the Pilbara fossils are a monument to the history of everything and everyone alive today. But the fossils' value is more than symbolic. There's a wealth of research still to be done to tease apart the secrets of those ancient ecosystems, and it's impossible to predict what new questions might arise and what research technologies will become available, said Allen.
"They're a library to Earth's past and life on our planet. And they need to be available to everybody now and in the future," said Allen.
One of the most exciting ways scientists are using the Pilbara fossils is as a guide for how to find life on Mars. The rocks in that part of Australia are thought to be similar to those where NASA's Perseverance Rover landed on Mars last month, with the Mars site holding a lake at the same time the Pilbara region contained a sea. If early life could thrive on Earth in such conditions, it could potentially have done so on Mars as well, said Mitch Schulte, a geologist and program scientist for NASA's Mars exploration program.
It's not enough for the Mars researchers to examine stromatolite specimens in a museum. Members of NASA and the European Space Agency have traveled all the way to Australia so they can envision what it will be like to guide a rover through such terrain, interpreting subtle clues that may help them locate fossils on Mars -- if they do exist.
"If your rover's going this way, would you have seen what we just saw? All that kind of stuff, that didn't really occur to me until I had actually been out there," said Schulte.
There's also a tremendous amount about the fossils in Australia that can only be understood from their place in the landscape. For example, the Pilbara cone-shaped stromatolites grew straight up toward the light, even when they were on a sloped surface. They also weren't perfectly round in cross-section, said Van Kranendonk; instead, they were oblong, angled so the narrow sides would meet the incoming and outgoing tides.
When you take a stromatolite fossil out of its environment, it loses most of its scientific value, according to multiple researchers. "It would sort of be like taking one organic molecule out of an organism and thinking you know everything there is to know about that organism," said Schulte. "You really need a bigger-picture story of what's going on."
Protecting a global treasureProtecting the fossil sites will be no easy task. They are remote, and while that helps reduce casual and accidental damage, it also makes them harder to monitor. And with the locations published in scientific journals, there is nothing to stop anyone who is determined to get there.
Fletcher's graduate thesis is devoted to figuring out how to save the stromatolites despite the challenges. As an interim measure, she is working to get security cameras installed at the most valuable sites. She also has a long-term vision that would see the area developed as a tourist destination and monitored by Nyamal rangers -- members of the Aboriginal people who are the traditional owners of the land. In interviews with local landowners, miners and other stakeholders, she has not yet encountered any opposition and has even received offers of funding from two mining companies.
Many of those plans may be on hold as advocates wait for additional legal processes to play out. For example, the state government of Western Australia is considering including three of the most important sites in a new national park, which might open up additional sources of funding for rangers and infrastructure. Martin at the Geological Survey of Western Australia supports the move, and hopes the national park status will also help people understand why the fossils should be preserved.
"I don't think people really get why we want to protect rocks, and they see stromatolites as just rocks in a lot of cases," she said. "But as soon as you put it into a national park, it's like, yep, everyone gets it."
Meanwhile, Fletcher and Van Kranendonk are lobbying to have four sites protected under a federal National Heritage listing; the application was submitted last month. A National Heritage listing would require development of a new management plan, which should make funding easier to secure.
"I think it's a fantastic initiative and effort from Claire and Martin [Van Kranendonk], and I fully support it, and so do most of the Nyamal people that are aware of it," said Jamie Haynes, Heritage Manager at Nyamal People's Trust. "What it means up here to us is simply that we've got some country there that's ancient -- more ancient than us, our culture -- and it's going to stay there."
In fact, the Nyamal people aren't waiting for National Park or National Heritage listings. Haynes recently secured a grant from the Western Australia Department of Biodiversity, Conservation and Attractions to start an Aboriginal ranger program. The grant will pay for six part-time rangers over the next two years, said Haynes. He hopes that in that time, the program can build up enough momentum and additional funding streams to offer long-term protection to the stromatolite fossils, as well as to archaeological sites and endangered wildlife.
Haynes used to tend livestock around the fossil sites, and often wondered about the strange bubbly-looking rocks. He said that when he learned what they were, it gave him a new sense of appreciation, making him realize the exceptional age of his peoples' land. He hopes to establish a training program to teach rangers about stromatolites and help them spot whether any have been tampered with.
It makes sense to Haynes why the earliest record of life on Earth should be left in place, where it can be understood as part of an intact and complex landscape.
"Aboriginal people view it as we're just passing through. We're not here to change it," he said. "We're here to keep it, maintain it, so that other people can pass through. And when you die you go back into that, you know, so that the hills become your ancestors."