Category: 7. Science

Our solar system’s latest and only third known interstellar visitor is becoming more fascinating by the week. 

Spotted in early July, the object, dubbed 3I/ATLAS, is widely believed to be a comet. It’s traveling so fast that one look at its speed was enough to let astronomers know that it came from untold thousands of light years away. And it may even be older than our entire solar system.

Now, the James Webb Space Telescope has turned its mighty eye — specifically, its Near-Infrared Spectrograph instrument — towards the object, furnishing us with more details about its size and composition to back up what other observatories, including the Hubble Space Telescope, had found previously. 

These findings were published in a new study by researchers at NASA and a host of universities, currently awaiting peer review. And one detail in it is especially tantalizing, as highlighted by Space.com: 3I/ATLAS has among the highest ever ratio of carbon dioxide to water ever observed in a comet. And it also appears that the ice entombed within the comet may have been exposed to higher levels of radiation than comes from our solar system, the authors found.

It’s a pristine sample of the greater cosmos delivered, serendipitously, right to our doorstep.

“Continued spectroscopic observations of interstellar objects have the potential to reveal crucial details on the physics and chemistry of planet formation in planetary systems other than our own,” reads the paper.

Comets are believed to form in large numbers during the formation of a planetary system, and can get ejected by gravitational encounters with larger objects, like planets, the authors explain. A mixture of rock, ice, and dust, these cosmic snowballs heat up as they near a star like our Sun, causing them to release a glowing cloud of gas called a coma, giving them their distinctive appearance.

The previous interstellar visitor, Borisov, was also believed to be a comet. Both have shown clear signs of cometary activity, such as possessing a coma. But Borisov was largely similar to the well-studied comets in our solar system, the authors wrote, save for unusual levels of carbon monoxide. 

With its extreme imbalance of water and carbon, 3I/ATLAS appears to be a far more remarkable object. One scenario that the unprecedentedly high ratio of carbon suggests is that the comet first formed in the circumstellar cloud of gas and dust that surrounds a nascent star called a protoplanetary disk — specifically, near a region called the CO2 ice line, where temperatures are low enough that CO2 molecules can freeze into a solid.

Alternatively, something could be preventing the Sun’s warmth from reaching deep into the comet’s nucleus, suppressing the sublimation of water ice into water vapor, the authors speculated.  

As we speak, 3I/ATLAS is storming towards the solar system’s center at over 138,000 miles per hour. Its speed, coupled with its trajectory, point to it originating from the center of the galaxy, possibly in a star system low in heavy elements. And to build up to such an incredible pace, it would have to be unimaginably ancient: perhaps 3 to 11 billion years old, previous research has estimated. The latest James Webb findings could help fill in more blanks about its origins and history.

3I/ATLAS is expected to reach perihelion, its closest distance to the Sun, around October 30 this year, coming within Mars’ orbit. Along the way, it’ll travel behind the Sun from our perspective — meaning for a while, it’ll be impossible to observe.

More on space: Scientist Says Mysterious Object Approaching Earth May Be Alien Artifact

A trip into outer space takes a toll on the human body, with low gravity atrophying muscles and eroding bones, causing astronauts to lose 1% of their mass every month.

Understanding how those conditions affect astronauts while also taking advantage of a low-gravity environment could help researchers make scientific progress much closer to home, not just to address specific diseases but to potentially create whole new classes of medicine.

“A lot of the changes that our bodies experience in microgravity mimic the conditions that our bodies see on Earth as we age, but it happens a lot faster,” said Heidi Parris, associate program scientist for NASA’s International Space Station Program, during a recent webinar.

For astronauts aboard the ISS, maintaining health requires effort, including daily two-hour workouts and careful nutrition. And while cell and tissue growth changes pose challenges for astronauts and mission support teams, they also offer opportunities for drug researchers looking to learn more about diseases.

SpaceX launched its CRS-33 cargo mission August 24 to the ISS carrying new research projects that scientists hope will speed drug discoveries and advances back on the ground.

Here are three unique benefits of microgravity that may accelerate the search for treatments to improve human health on Earth.

Enhanced growth of 3D structures

Arun Sharma, director of the Center for Space Medicine at Cedars-Sinai Medical Center, said that the low gravity environment of the ISS may help engineers grow 3-dimensional models called organoids, which are used to study diseases, drug response and toxicology. Induced pluripotent stem cells, adult somatic cells that can be reprogrammed to a stem-like state, form the basis for these models. 

“Organoids are an extension of those induced pluripotent stem cells,” Sharma said. “They’re basically three-dimensional cell aggregates that are revolutionizing stem cell biology and biomedical research right now.”

Organoids can be grown here, but scientists suspect these spherical tissues may be of better quality if grown in microgravity, free from the compressing effects of gravity. 

“After a month [on the ISS] they’ll be returned to Earth and the Cedars-Sinai laboratory for genetic and imaging analyses,” Sharma said. The hope is that they will be a structural improvement over their home-grown counterparts, potentially opening the door to mass production for a variety of critical applications. 

Currently, Sharma uses organoids to study how cancer treatments affect the heart, but they can also be used to test efficacy or study conditions like heart disease. As their complexity grows, brain models could help gain a better understanding of neurodegenerative diseases such as Parkinson’s disease, Huntington’s disease and ALS.

Revealing hidden drivers of bone loss

Astronauts in microgravity lose bone 12 times faster than on Earth, inspiring scientists to take bone research into outer space. Dr. Abba Zubair, medical director and researcher at the Mayo Clinic in Jacksonville, Florida, said his team is seeking to better understand the mechanism behind bone loss and formation by taking their research to the ISS. 

The human body continually breaks down and rebuilds bone through a process involving a complex network of mesenchymal stem cells, osteoblasts, osteocytes and osteoclasts. But Zubair suspects another factor may drive this process: inflammation triggered by a cell cytokine, interleukin-6, and understanding how that happens in low gravity could reveal new insights.. 

Their research aims to understand this mechanism and provide the foundation for drugs that might one day modulate this effect to keep bones healthy both in people on this planet and astronauts in space, he said.

Compressing drug development timelines

The accelerated degradation of bone, heart and muscle induced by microgravity offers an advantage in drug development, Sharma said.  

“One thing we’re always interested in here on the ground, terrestrially, is ways to accelerate the timelines for drug discovery, for discovering new drugs that would be able to help improve cardiac conditioning, or perhaps treat diseases such as ALS or Parkinson’s,” he said.

These timelines typically take years on Earth, but using organoids to study these illnesses in space could accelerate that timeline. 

Greenland, despite its name, is largely blanketed in ice. And beneath that white expanse lies a world of hidden lakes. Researchers have now used satellite observations to infer that one such subglacial lake recently burst through the surface of the Greenland Ice Sheet, an unexpected and unprecedented event. By connecting this outburst with changes in the velocity and calving of a nearby glacier, the researchers helped to unravel how subglacial lakes affect ice sheet dynamics. These results were published in Nature Geoscience.

Researchers have known for decades that pools of liquid water exist beneath the Antarctic Ice Sheet, but scientific understanding of subglacial lakes in Greenland is much more nascent. “We first discovered them about 10 years ago,” said Mal McMillan, a polar scientist at Lancaster University and the Centre for Polar Observation and Modelling, both in the United Kingdom.

Subglacial lakes can exert a significant influence on an ice sheet. That’s because they affect how water drains from melting glaciers, a mechanism that in turn causes sea level rise, water freshening, and a host of other processes that affect local and global ecosystems.

McMillan is part of a team that recently studied an unusual subglacial lake beneath the Greenland Ice Sheet. The work was led by Jade Bowling, who was a graduate student of McMillan’s at the time; Bowling is now employed by Natural England.

Old, but Not Forgotten, Data

In the course of mining archival satellite observations of the height of the Greenland Ice Sheet, the team spotted something unusual in a 2014 dataset: An area of roughly 2 square kilometers had dropped in elevation by more than 80 meters (260 feet) between two satellite passes just 10 days apart. That deflation reflected something going on deep beneath the surface of the ice, the researchers surmised.

A subglacial lake that previously was situated at the interface between the ice and the underlying bedrock must have drained, said McMillan, leaving the ice above it hanging unsupported until it tumbled down. The team used the volume of the depression to estimate that roughly 90 million cubic meters (more than 3.1 billion cubic feet) of water had drained from the lake between subsequent satellite observations, making the event one of Greenland’s biggest subglacial floods in recorded history.

Subglacial lakes routinely grow and shrink, however, so that observation by itself wasn’t surprising. What was truly unexpected lay nearby.

“We also saw an appearance, about a kilometer downstream, of a huge area of fractures and crevassing,” McMillan said. And beyond that lay 6 square kilometers (2.3 square miles)—an area roughly the size of lower Manhattan—that was unusually smooth.

The researchers concluded that after the subglacial lake drained, its waters likely encountered ice frozen to the underlying bedrock and were forced upward and through the surface of the ice. The water then flowed across the Greenland Ice Sheet before reentering the ice several kilometers downstream, leaving behind the polished, 6-square-kilometer expanse.

“This was unexpected,” said McMillan. “We haven’t seen this before.”

A Major Calving, a Slowing Glacier

It’s most likely that the floodwater traveled under northern Greenland’s Harder Glacier before finally flowing into the ocean.

Within the same 10-day period, Harder Glacier experienced its seventh-largest calving event in the past 3 decades. It’s impossible to know whether there’s a direct link between the subglacial lake draining and the calving, but it’s suggestive, said McMillan. “The calving event that happened at the same point is consistent with lots of water flooding out” from the glacier.

The team also found that Harder Glacier rapidly decelerated—3 times more quickly than normal—in 2014. That’s perhaps because the influx of water released by the draining lake carved channels in the ice that acted as conduits for subsequent meltwater, the team suggested. “When you have normal melting, it can just drain through these channels,” said McMillan. Less water in and around the glacier means less lubrication. “That’s potentially why the glacier slowed down.”

That reasoning makes sense, said Winnie Chu, a polar geophysicist at the Georgia Institute of Technology in Atlanta who was not involved in the research. “It’s like you riding on a waterslide versus a rockslide. You’re going to slide a lot faster on the waterslide.”

Just a One-Off?

In the future, McMillan and his colleagues hope to pinpoint similar events. “We don’t have a good understanding currently of whether it was a one-off,” he said.

Getting access to higher temporal resolution data will be important, McMillan added, because such observations would help researchers understand just how rapidly subglacial lakes are draining. Right now, it’s unclear whether this event occurred over the course of hours or days, because the satellite observations were separated by 10 days, McMillan said.

It’s also critical to dig into the mechanics of why the meltwater traveled vertically upward and ultimately made it to the surface of the ice sheet, Chu said. The mechanism that this paper is talking about is novel and not well reproduced in models, she added. “They need to explain a lot more about the physical mechanism.”

But something this investigation clearly shows is the value of digging through old datasets, said Chu. “They did a really good job combining tons and tons of observational data.”

—Katherine Kornei (@KatherineKornei), Science Writer

Citation: Kornei, K. (2025), A burst of subglacial water cracked the Greenland Ice Sheet, Eos, 106, https://doi.org/10.1029/2025EO250317. Published on 28 August 2025.

Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

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Micrometeorites, unlike their larger brethren, rarely get a spotlight at museums. But there’s plenty to learn from these extraterrestrial particles, despite the largest of them measuring just millimeters across.

Nearly 50 tons of extraterrestrial material fall on Earth every day, and the majority of that cosmic detritus is minuscule. Micrometeorites are, by definition, smaller than 2 millimeters in diameter, and they’re ubiquitous, said Fabian Zahnow, an isotope geochemist at Ruhr-Universität Bochum in Germany. “You can basically find them everywhere.”

Researchers recently analyzed fossilized micrometeorites that fell to Earth millions of years ago. They extracted whiffs of atmospheric oxygen incorporated into the particles and showed that carbon dioxide (CO₂) levels during the Miocene and Cretaceous did not differ wildly from modern-day values. The results were published in Communications Earth and Environment.

Extraterrestrial Needles in Rocky Haystacks

Newly fallen micrometeorites can be swept from rooftops and dredged from the bottoms of lakes.

Zahnow and his collaborators, however, opted to turn back the clock: The team analyzed a cadre of micrometeorites that fell to Earth millions of years ago and have since been fossilized. The team sifted through more than a hundred kilograms of sedimentary rocks, mostly unearthed in Europe, to discover 92 micrometeorites rich in iron. They added eight other iron-dominated micrometeorites from personal collections to bring their sample to 100 specimens.

Metal-rich micrometeorites such as these are special, said Zahnow, because they function like atmospheric time capsules. As they hurtle through the upper atmosphere on their way to Earth, they melt and oxidize, meaning that atmospheric oxygen gets incorporated into their otherwise oxygen-free makeup.

“When we extract them from the rock record, we have our oxygen, in the best case, purely from the Earth’s atmosphere,” said Zahnow.

Ancient Carbon Dioxide Levels

And that oxygen holds secrets about the past. It turns out that atmospheric oxygen isotope ratios—that is, the relative concentrations of the three isotopes of oxygen, ¹⁶O, ¹⁷O, and ¹⁸O—correlate with the amount of photosynthesis occurring and how much CO₂ is present at the time. That fact, paired with model simulations of ancient photosynthesis, allowed Zahnow and his colleagues to infer long-ago atmospheric CO₂ concentrations.

Reconstructing Earth’s atmosphere as it was millions of years ago is important because atmospheric gases affect our planet so fundamentally, said Matt Genge, a planetary scientist at Imperial College London not involved in the work. “The story of the atmosphere is the story of life on Earth.”

But Zahnow and his collaborators first had to make sure the oxygen in their micrometeorites hadn’t been contaminated. Terrestrial water, with its own unique oxygen isotope ratios, can seep into micrometeorites that would otherwise reflect atmospheric oxygen isotope ratios from long ago. That’s a common problem, said Zahnow, given the ubiquity of water on Earth. “There’s always some water present.”

The team found that the presence of manganese in their micrometeorites was a tip-off that contamination had occurred. “Extraterrestrial metal has basically no manganese,” said Zahnow. “Manganese is really a tracer for alteration.”

Unfortunately, the vast majority of the researchers’ micrometeorites contained measurable quantities of manganese. In the end, Zahnow and his collaborators deemed that only four of their micrometeorites were uncontaminated.

Those micrometeorites, which fell to Earth during the Miocene (9 million years ago) and the Late Cretaceous (87 million years ago), suggested that CO₂ levels during those time periods were, on average, roughly 250–300 parts per million. That’s a bit lower than modern-day levels, which hover around 420 parts per million.

The team’s findings are consistent with values suggested previously, said Genge, but unfortunately, the team’s numbers just aren’t precise enough to conclude anything meaningful. “You have a really huge uncertainty,” he said.

The team’s methods are solid, however, said Genge, and the researchers made a valiant effort to measure what are truly faint whiffs of ancient oxygen. “It’s a brave attempt.”

In the future, it would be valuable to collect a larger number of pristine micrometeorites dating to time periods when model reconstructions suggest anomalously high CO₂ levels, said Zahnow. “What we really hoped for was to get pristine micrometeorites from periods where the reconstructions say really high concentrations.”

Confirming, with data, whether such time periods, such as the Triassic, truly had off-the-charts CO₂ levels would be valuable for understanding how life on Earth responded to such an abundance of CO₂.

—Katherine Kornei (@KatherineKornei), Science Writer

Citation: Kornei, K. (2025), Fossilized micrometeorites record ancient CO₂ levels, Eos, 106, https://doi.org/10.1029/2025EO250319. Published on 28 August 2025.

Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

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Researchers in Taiwan have observed sheet web spiders (Psechrus clavis) capturing fireflies and leaving them glowing in their webs for up to an hour. This unusual tactic turns the fireflies’ mating signals into a deadly lure, with other insects attracted to the light before becoming trapped themselves.

Keen to find out more about the hunting strategy, scientists from Tunghai University devised a field experiment in the Xitou Nature Education Area – a mountainous forest park in the heart of the country.

Here, under the cover of darkness, they placed LEDs designed to mimic firefly light in some spider webs, while leaving other webs empty as controls.

The results, published in the Journal of Animal Ecology, show that webs with lights attracted three times more prey than unlit webs, and in the case of fireflies specifically, capture rates increased tenfold.

“Our findings highlight a previously undocumented interaction where firefly signals, intended for sexual communication, are also beneficial to spiders,” explains Dr I-Min Tso, lead author of the study.

“This study sheds new light on the ways that nocturnal sit-and-wait predators can rise to the challenges of attracting prey and provides a unique perspective on the complexity of predator-prey interactions.”

The study also revealed that most of the glowing fireflies caught in webs were males, likely mistaking the bioluminescence of trapped individuals for potential mates.

Video footage captured during the research shows spiders treating prey differently: moths were eaten immediately, while fireflies were left alive, continuing to emit their mating signals.

“Handling prey in different ways suggests that the spider can use some kind of cue to distinguish between the prey species they capture and determine an appropriate response,” says Dr Tso.

“We speculate that it is probably the bioluminescent signals of the fireflies that are used to identify fireflies enabling spiders to adjust their prey handling behaviour accordingly.”

Unlike anglerfish and other predators that invest energy in producing their own lures, the sheet web spider appears to save energy by outsourcing this function to its prey.

The researchers suggest this adaptation may have evolved as a cost-effective strategy for survival in subtropical forests of East Asia, where both the spider and its main prey, the winter firefly (Diaphanes lampyroides), are found.

The study notes that although the LED mimics were a close match to real fireflies, future experiments using live insects would provide stronger evidence of this remarkable strategy.

Top image: fireflies in Taiwanese forest. Credit: Getty

More amazing wildlife stories from around the world

The International Space Station’s crew conducted critical research focused on studying the effects of microgravity on astronaut health, while also managing new cargo and conducting an emergency drill.

The research aimed at analysing the headward fluid shifts in space that lead to “puffy face” syndrome and potential vision changes.

The experiment is led by Kimiya Yui, flight engineer from the Japan Aerospace Exploration Agency (JAXA), who is testing a specialized thigh cuff on National Aeronautics and Space Administration (NASA) astronaut Mike Fincke.

The device will help to mitigate fluid buildup, minimizing pressure on the eyes and brain.

The thigh cuff investigation analyzes whether leg cuffs can counteract these fluid movements, possibly protecting astronauts for future Moon and Mars missions.

Yui conducted ultrasound scans on Fincke’s legs while his cardiac activity was being monitored by the electrodes, providing real-time health data to ground-based researchers.

In microgravity, astronauts experience Space-Associated Neuro-Ocular Syndrome (SANS). This condition leads to changes in vision due to fluid shifts towards the head.

Previous studies, such as, Fluid Shifts suggested that changing carbon dioxide levels and B vitamins altered brain damage and caused symptom severity.

Canadian research (SANSORI) found that spaceflight reduces eye tissue stiffness, similar to conditions on Earth, such as those associated with glaucoma. 

Another research conducted by Japanese researchers found that artificial gravity may prevent genetic changes in eye tissues. 

FRANKFURT. When a tree dies, it forms the foundation for new life: In a slow, invisible process, leaves, wood and roots are gradually decomposed – not by wind or weather but by millions and millions of tiny organisms. Fungi thread their way through the dead wood and degrade cell walls. Tiny animals such as insect larvae and mites gnaw through the tissue. And something very important happens in the process: The carbon stored in the plant is released, ultimately placing it at the disposal of plants again for the purpose of photosynthesis. But what exactly is responsible for performing this task in the global carbon cycle? And which molecular tools do the organisms use for it? To answer these questions, the researchers have developed a new bioinformatics-based method, which they have now presented in Molecular Biology and Evolution.

18,000 species in the spotlight

This method, called fDOG (Feature architecture-aware directed ortholog search), makes it possible to search in the genetic material of various organisms for genes that have evolved from the same precursor gene. It is assumed that these genes, known as “orthologs”, encode proteins with similar functions. For the current study, the scientists searched for the genes of plant cell wall-degrading enzymes (PCDs). Unlike previous methods, fDOG not only searches through masses of genomic information but also analyzes the architecture of the proteins found – i.e. their structural composition, which reveals a lot about an enzyme’s function.

“We start with a gene from one species, referred to as the seed, and then trawl through tens of thousands of species in the search for orthologous genes,” explains Ingo Ebersberger, Professor for Applied Bioinformatics at Goethe University Frankfurt. “In the process, we constantly monitor whether the genes we find perhaps differ from the seed in terms of function and structure – for example, through the loss or gain of individual areas relevant for function.”

The research team used this method to search for more than 200 potential PCD candidates in over 18,000 species from all three domains of life – bacteria, archaea and eukaryotes (plants, animals, fungi). The result is a detailed global map – with unprecedented accuracy – of enzymes capable of degrading plant cell walls.

Surprising discoveries among fungi and animals

The researchers devised special visualization methods to analyze the vast amounts of data and detect patterns. This revealed characteristic changes in the enzyme repertoire of the fungi under study, indicating a change in lifestyle of certain fungal species: From a decomposing lifestyle – i.e. the degradation of dead plants – to a parasitic lifestyle in which they infest living animals. Such evolutionary transitions are mirrored in characteristic patterns of enzyme loss.

A special surprise in the animal kingdom was the discovery that some arthropods possess an unexpectedly wide range of plant cell wall-degrading enzymes. These enzymes presumably originated from fungi and bacteria and entered the genome of invertebrates via direct gene transfer between different organisms – i.e. horizontal gene transfer. This suggests that they might be able to degrade plant material independently and are not reliant on the bacteria in their intestines, as was previously assumed. In another case, however, it emerged that the potential PCD genes in the analyzed sequence could be ascribed to microbial contamination – an important sign that such data need to be checked very carefully.

New insights into the global carbon cycle

The study shows how fDOG can be used to systematically map biological capabilities across the entire tree of life – from broad-scale overviews to detailed investigations of individual species. With this method, it is possible both to track evolutionary trajectories and to identify players previously overlooked in the global carbon cycle. Since soils contain large amounts of dead plant material and therefore constitute the largest terrestrial carbon sink, the decomposition of plant material is an important driver of the global carbon cycle. “Our method gives us a fresh view of how metabolic capacities are distributed across the tree of life,” says Ebersberger. “We can now conduct multi-scale analyses and in the process detect both recent evolutionary changes and large patterns.”

A skull that was found embedded in a cave wall in Greece more than 60 years ago may finally have an identification.

A new dating of the minerals that surrounded and grew over the mysterious Petralona skull places its age at 277,000 years at least – and suggesting it is a member of a primitive, extinct hominid that lived alongside Homo neanderthalensis.

“From a morphological point of view,” writes a team led by geochronologist Christophe Falguères of the Institute Of Human Paleontology in France, “the Petralona hominin forms part of a distinct and more primitive group than Homo sapiens and Neanderthals, and the new age estimate provides further support for the coexistence of this population alongside the evolving Neanderthal lineage in the later Middle Pleistocene of Europe.”

Related: Ancient Egyptian Skull Found Riddled With Tiny Cut Marks. This Could Be Why.

The Petralona skull was uncovered in 1960 in Petralona Cave, not far from Thessaloniki in Greece. In the protected darkness of the inner chamber, the skull had been fused to the wall by a gradual accretion of calcite – a stalagmite protruding, unicorn-like, from its forehead.

Although the lower jaw was missing, this method of preservation had protected the cranium for what seemed to be many millennia, giving paleontologists an intact specimen to study – but a specimen of what, they couldn’t agree.

Attempts at dating the skull placed its age anywhere between 170,000 and 700,000 years, and analyses of its structure and shape had it placed as Homo sapiens, Homo neanderthalensis, or Homo heidelbergensis, depending who was doing the work.

These are questions that have never quite been fully resolved. Falguères and his team thought the minerals of the cave might have some answers. In their new research effort, they have conducted a detailed dating analysis, and examined the previous 45 years of data currently available on the cave and the skull.

Their work involved a precision technique called uranium-thorium dating, which is possible thanks to the specific conditions that can be found in caves. Water seeps through the rock and drips down, depositing any minerals inside it as it goes. Over time, this creates layers upon layers of calcite, eventually building deposits called speleotherms, which include stalagmites and stalactites.

When speleotherms form, they sequester tiny amounts of radioactive uranium locked inside. Over time, that uranium decays into thorium at a very precise rate.

We also know that any thorium in the speleotherm has to be the product of uranium decay, because thorium isn’t water soluble, but uranium is – so there could have been no thorium in the water that deposited the minerals. So, scientists can then look at the ratio of uranium to thorium in a sample, and determine exactly how old it is, based on the uranium decay rate.

Falguères and his colleagues used this technique to date the calcite that formed directly onto the skull – the first film of calcite directly over the bone. They also dated three samples taken from separate samples on the cave wall, with the oldest deposit being 539,000 years old.

If the skull was in direct contact with the cave wall from the beginning, it would be between 277,000 and 539,000 years old. If the skull was not originally attached to the wall but deposited there later, it would be between 277,000 and 410,000 years old.

The anatomy of the skull is distinct from both Homo sapiens and Neanderthals, which leaves open the tantalizing possibility that the Petralona skull belonged to a Homo heidelbergensis individual, a species whose place in the hominid family tree remains under debate.

The skull bears some striking similarities to a skull found in a cave in Kabwe, Zambia. The Kabwe skull has been dated to around 300,000 years ago, and is now generally classified as Homo heidelbergensis. This could help identify the Petralona skull in future work.

“Our results from dating the matrix attached to the Petralona cranium suggest that like the Kabwe cranium, the Petralona cranium may date to about 300,000 years ago, consistent with their persistence into the later Middle Pleistocene,” the researchers write.

The paper has been published in the Journal of Human Evolution.