As an undergraduate at the University of New South Wales, Dr. Erica Barlow picked up a rock that would change her life and potentially alter our understanding of the history of life on Earth. However, it took a long time to determine what she had found, and even today, there remains some uncertainty about the rock’s contents.

Barlow was in Western Australia’s Pilbara region to study stromatolites, some of the oldest known fossils. During one of the long walks between the campsite and the fossils, she noticed a shiny black rock reflecting the setting sun against the region’s famous red dirt. She picked it up as a memento of the trip. “I kept it on my desk as a kind of pet rock while I wrote my honors thesis,” Barlow said in a statement.

While Barlow was still focused on stromatolites, her supervisor, Martin Van Kranendonk, noticed the rock and identified it as black chert. He informed her that black chert has been known to contain microfossils from early in Earth’s history, although this is debated. He suggested she examine it further. Despite being buried in her thesis work, Barlow eventually prepared and examined a sample, and was astonished by what she found.

Fossils in the chert looked like nothing Barlow had seen before. Moreover, no one else had seen anything like them either. Given the chert’s age, if there were any microfossils inside they were expected to be of single-celled organisms. The microfossils Barlow had found look more like a soccer ball: almost round, but with a complex outline and an internal honeycomb structure.

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

That’s a significant claim under any circumstances, but especially when the chert was thought to date back long before complex life was believed to have appeared.

The stromatolites Barlow had been studying are structures formed by thousands of cells layering themselves with sand. However, these are not considered complex life forms.

Up until now, it was believed that the first complex life forms were hundreds of millions of years younger than Barlow’s discovery. Her find could be an early predecessor of eukaryotes, the branch of life that includes animals, plants, fungi, and algae. Alternatively, it might represent an evolutionary dead-end, an early experiment in complexity that didn’t survive. There’s also a possibility it could be an illusion, mimicking complexity in an unexplained way.

To explore these possibilities, Barlow decided to make the rock the subject of her PhD.

First, she needed to determine if the chert was unique. Returning to the collection site quickly provided an answer. Barlow discovered a rock wall covered with thousands of black chert nodules 30 meters (100 feet) up a nearby slope. Like the Pilbara region itself, the wall extended out of view in both directions. Barlow told IFLScience she has since measured the formation at 12 kilometers (7 miles) long, with chert nodules averaging 20 centimeters (8 inches) wide and 7 centimeters (3 inches) high.

Many chert samples appear to contain no fossils at all, while others hold organisms resembling those found globally from this period—“either long thin filaments or unicells—like bubbles,” Barlow told IFLScience. A scientist who collected a small sample might easily conclude there was nothing unusual.

Aware of the potential significance of her discovery and the need for replication, Barlow collected hundreds of samples. Back in Sydney, she found several that contained specimens resembling her original find, with some even having amber spheres within the honeycomb shapes. She has now expanded her collection to 19 specimens, including half a dozen from a single rock. Among her hundreds of samples are some that might have originally looked similar but are too degraded for her to be certain. If she had picked up one of these instead, she might not have recognized its value.

The chert samples are clearly of the same age, and independent testing confirmed they all formed about 2.4 billion years ago. Crucially, this date aligns with the now widely accepted timing of the Great Oxidation Event, a period when oxygen levels in the atmosphere and oceans rose dramatically, making it possible for complex life to develop.

Previously, there had been an unexplained gap of around 750 million years between the availability of oxygen and the first eukaryote fossils, suggesting that something was taking advantage of the increased oxygen.

However, none of the specimens Barlow has found can be definitively proven to be predecessors of eukaryotes.

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

Geneticists use “molecular clocks” to estimate the timing of major advances in life, but Barlow told IFLScience that these produce “a huge range of estimates” for when eukaryotes emerged. Some estimates are close to the age of her chert, while others are hundreds of millions of years later. “One problem is that molecular clocks are informed by the fossil record, which makes it a bit grey when you look back this far, where the fossil record is so patchy,” she said.

Theoretically, chemical analysis could provide valuable evidence. “If we can identify the type of carbon, it might tell us what the organism ate,” Barlow said, potentially proving its complexity. However, this is nearly impossible because samples are so easily contaminated with modern carbon.

“Working with such tiny fossils, with so little carbon, if we got a positive result, the scientific community would not believe it due to the possibility of contamination,” Barlow told IFLScience.

Future technology might improve the process, but in the meantime, Barlow’s work has struggled to gain recognition. The remoteness of the location might be part of the problem. When the oldest animals were found in the Ediacaran Hills in South Australia, many paleobiologists refused to believe they were real until they saw them personally, which was a slow process due to the location.

If similar fossils were found elsewhere, it might help Barlow’s case, especially if something slightly later showed signs of further development. So far, nothing has turned up. Barlow admitted to IFLScience this could be the only evidence of an early experiment with complexity that was snuffed out and did not reoccur for a long time.

On the other hand, the lack of another location is not entirely surprising given how few sites preserve fossils more than 1.6 billion years old. “There are 600-700 million years represented by a handful of sites on the planet,” Barlow told IFLScience. Preserving a fossil site is not easy, but Barlow thinks such an extreme shortage may be due to the state of plate tectonics at the time.

If these specimens are ancestral eukaryotes, they wouldn’t have looked very exciting by modern standards. “From what we can tell, the life would have been soft, squishy, and gooey—kind of like slime at the edge of a pond,” Barlow said. Nevertheless, Van Kranendonk noted the similarity to modern eukaryotic algae.

While Barlow waits for further developments that could shed more light on her discovery, she has completed a postdoc with NASA in the Laboratory for Agnostic Biosignatures. There, she worked on designing ways to identify life on other worlds if it doesn’t resemble Earth life, giving her about the best training available for such a task.