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As a student at the University of New South Wales, Dr Erica Barlow picked up a rock that would change her life and quite possibly the way we see the history of life on Earth. It took a long time to figure out what she had, however, and even today no one can be sure that the rock contained what Barlow and others suspected.

Barlow was in the Pilbara region of Western Australia to study stromatolites, some of the oldest fossils we know. The trip involved many long walks between the campsite and the fossils; on a return trip, Barlow spotted a shiny black rock that caught the setting sun against the famous red dirt of the area. She took it as a souvenir of the trip. “I kept it on my desk as a pet rock while I wrote mine [honors] thesis,” Barlow said in a statement.

Barlow was still working on the stromatolites when her supervisor, Martin Van Kranendonk, spotted the rock and identified it as black cream. Kranendonk told her that the black cream was known to contain microfossils from the beginning of life on Earth (although this is debated) and suggested she check it out. Buried in her dissertation, Barlow needed little encouragement to take the time to prepare and examine a sample, but was amazed when she did.

The fossils in the pottery were unlike anything Barlow had seen before. Especially since no one else has seen anything like it. Given the age of the skull, if there were any microfossils inside, they would be expected to be from single-celled organisms. The microfossils found by Barlow look more like a soccer ball: almost round, but with complex contours and an internal honeycomb structure.

“There was nothing else like a microfossil that I found in the geologic record,” Barlow said.

That’s a big claim under any circumstances, but considerably bigger when the cherry was thought to date back to long before complex life was thought to have emerged.

The stromatolites that Barlow studied include thousands of cells that collectively form layered structures from their own bodies and sand. However, they are not what we think of as complex life.

As far as anyone knows, the first complex life forms were hundreds of millions of years younger than this discovery. Barlow’s find may be an ancestor of eukaryotes, the branch of the tree of life that includes all animals, plants, fungi and algae. Or it could be an evolutionary dead end, an early flowering of complexity that has been extinguished. On the other hand, it might just be an illusion, mimicking complexity in some way we can’t explain.

There was only one thing to do – to make rock the subject of her Ph.D.

First, Barlow needed to know if the handwriting was unique. Returning to the assembly point answered almost immediately. Barlow discovered a rock wall studded with thousands of black patterned nodules 30 meters (100 ft) up a nearby slope. Like the Pilbara itself, the wall stretched out of sight in both directions. Barlow told IFLScience that she has since measured the formation 12 kilometers (7 miles) long, all laden with cream nodules averaging 20 centimeters (8 inches) wide and 7 centimeters (3 inches) high.

Many cream samples appear to contain no fossils at all. Others have organisms that look like those found around the world from that time — “either long thin filaments or single-celled — like bubbles,” Barlow told IFLScience. A scientist who has collected a small sample can easily go home thinking there is nothing out of the ordinary.

Realizing the potential significance of his discovery, however, and the need to replicate it, Barlow collected hundreds of samples. Back in Sydney, she found several contained specimens that resembled her original, some even having honeycomb-shaped amber spheres. She has now expanded the specimens to 19, including half a dozen from one rock. Barlow’s hundreds of samples also contain some that may have originally looked similar, but were too degraded for her to be sure. If she had taken one of these instead, she probably wouldn’t have recognized its value.

The core samples are apparently the same age, and independent testing has confirmed that they all formed around 2.4 billion years ago. Crucially, this coincides with the date geologists have now settled on – after much debate – for the Great Oxidation Event. This is when oxygen levels in the atmosphere and oceans rise so dramatically that breathing becomes possible, opening the door to complex life.

Before that, there was an unexplained gap of about 750 million years between the appearance of oxygen and the first eukaryote fossils, indicating that something took advantage of it.

Unfortunately, however, none of the specimens Barlow found could be proven to be progenitors of eukaryotes.

“When you’re working with material from that time, it’s really hard to prove or disprove something like this because we just don’t have enough information preserved,” Barlow said in the statement.

Geneticists time the great advances in life using “molecular clocks,” but Barlow told IFLScience that they give a “huge range of estimates” for when eukaryotes arose. Some of them are close to the age of her grant, but others are hundreds of millions of years later. “One of the problems is that molecular clocks are informed by the fossil record, which makes it a bit gray when you look back so far, where the fossil record is so patchy,” she said.

There are 6-700 million years represented by a handful of places on the planet.

Dr. Erica Barlow

In theory, chemical analysis can provide valuable evidence. “If we can identify the type of carbon, that can tell us what the organism ate,” she said, potentially proving its complexity. However, this is almost impossible because the samples are so easily contaminated with carbon from the modern world.

“Working with such small fossils, with so little carbon, if we get a positive result.” [scientific] the community won’t believe it because of the possibility of contamination,” Barlow told IFLScience.

Some future technology may improve the process, but in the meantime Barlow’s work struggles to gain recognition. The remoteness of the location may be part of the problem. When the oldest animals were found in the Ediacaran Hills of South Australia, many paleobiologists refused to believe they were real until they saw them in person. The location made this a slow process.

If similar fossils are found elsewhere in the world, it could help Barlow’s case, especially if something a little later shows signs of further development. So far nothing has appeared. Barlow admitted to IFLScience that this may be the only evidence of an early complex experiment that was suppressed and not repeated for a long time.

On the other hand, the lack of another location is not entirely surprising given how few places preserve fossils older than 1.6 billion years. “There are 6-700 million years represented by a handful of places on the planet,” Barlow told IFLScience. It is not easy to preserve a fossil, but Barlow believes that such an extreme scarcity may be a consequence of the state of plate tectonics at the time.

If these specimens were eukaryotic ancestors, they wouldn’t look very exciting by modern standards. “From what we can tell, life would be soft, slippery, and sticky — kind of like the slime you see at the edge of a lake,” Barlow said in the statement. However, Van Kranendonk noted the similarity to modern eukaryotic algae,

While Barlow waits for something to break open that might help us learn more about her discovery, she completed a postdoc with NASA at the wonderfully named Agnostic Biosignatures Laboratory. There she tried to design ways to identify life on other worlds if it didn’t look like life on Earth; she may have had the best training there is for such a task.

Barlow’s latest research on the discovery is published open access in Geobiology.