The Great Oxygenation Event (GOE) occurred around 2.3 billion years ago and marked the rise of atmospheric oxygen, likely triggered by green Cyanobacteria that used sunlight to split water, subsequently converting carbon dioxide into oxygen through photosynthesis. The result is that the current atmosphere is around 78% nitrogen and 21% oxygen, with only traces of other gases such as methane and carbon dioxide, which might have played a greater role before the rise of oxygen. The GOE fundamentally changed the course of life on Earth. This high amount of oxygen allows us animals to breathe, but it also complicates life for ancient life forms, which were almost unaware of the O₂ molecule. Understanding how these ancient microbes adapted to the presence of oxygen remains a major question.

To answer this, the team studied five hot springs in Japan, which are rich in varied water chemistries. Those five springs (one in Tokyo, two each in Akita and Aomori prefectures) are naturally rich in ferrous iron (Fe²⁺). They are rare in today’s oxygen-rich world because ferrous iron quickly reacts with oxygen and turns into an insoluble ferric iron form (Fe³⁺). But in these springs, the water still contains high levels of ferrous iron, low levels of oxygen, and a near-neutral pH, conditions thought to resemble parts of the early Earth’s oceans.

“These iron-rich hot springs provide a unique natural laboratory to study microbial metabolism under early Earth-like conditions during the late Archean to early Proterozoic transition, marked by the Great Oxidation Event. They help us understand how primitive microbial ecosystems may have been structured before the rise of plants, animals, or significant atmospheric oxygen,” says Shawn McGlynn, who supervised Li-Hau during her dissertation work.

In four of the five hot springs, the team found microaerophilic iron-oxidising bacteria to be the dominant microbes. These organisms thrive in low-oxygen conditions and use ferrous iron as an energy source, converting it into ferric iron. Cyanobacteria, known for producing oxygen through photosynthesis, were also present but in relatively small numbers. The only exception was one of the Akita hot springs, where non-iron-based metabolisms were surprisingly dominant.

Using metagenomic analysis, the team assembled over 200 high-quality microbial genomes and used them to analyse in detail the functions of microbes in the community. The same microbes that coupled iron and oxygen metabolism converted a toxic compound into an energy source and helped maintain conditions that allowed oxygen-sensitive anaerobes to persist. These communities carried out essential biological processes such as carbon and nitrogen cycling, and the researchers also found evidence of a partial sulfur cycle, identifying genes involved in sulfide oxidation and sulfate assimilation. Given that hot springs contained very little sulfur compounds, this was a surprising discovery. The researchers propose that this may indicate a “cryptic” sulfur cycle, where microbes recycle sulfur in complex ways that are not yet fully understood.

“Despite differences in geochemistry and microbial composition across sites, our results show that in the presence of ferrous iron and limited oxygen, communities of microaerophilic iron oxidisers, oxygenic phototrophs, and anaerobes consistently coexist and sustain remarkably similar and complete biogeochemical cycles,” says Li-Hau.

The research suggests a shift in our understanding of early ecosystems, showing that microbes may have harnessed energy from iron oxidation and oxygen produced by early phototrophs. The study proposes that, similar to these hot springs, early Earth hosted ecosystems were composed of diverse microbes, including iron-oxidising bacteria, anaerobes, and Cyanobacteria living alongside one another and modulating oxygen concentrations.

“This paper expands our understanding of microbial ecosystem function during a crucial period in Earth’s history, the transition from an anoxic, iron-rich ocean to an oxygenated biosphere at the onset of the GOE. By understanding modern analogue environments, we provide a detailed view of metabolic potentials and community composition relevant to early Earth’s conditions,” says Li-Hau.

Together, these insights deepen our understanding of life’s early evolution on Earth and have implications for the search for life on other planets with geochemical conditions similar to those of early Earth.

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Earth-Life Science Institute (ELSI) is one of Japan’s ambitious World Premiere International research centers, whose aim is to achieve progress in broadly inter-disciplinary scientific areas by inspiring the world’s greatest minds to come to Japan and collaborate on the most challenging scientific problems. ELSI’s primary aim is to address the origin and co-evolution of the Earth and life.

Institute of Science Tokyo (Science Tokyo) was established on October 1, 2024, following the merger between Tokyo Medical and Dental University (TMDU) and Tokyo Institute of Technology (Tokyo Tech), with the mission of “Advancing science and human wellbeing to create value for and with society.”

World Premier International Research Center Initiative (WPI) was launched in 2007 by Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT) to foster globally visible research centers boasting the highest standards and outstanding research environments. Numbering more than a dozen and operating at institutions throughout the country, these centers are given a high degree of autonomy, allowing them to engage in innovative modes of management and research. The program is administered by the Japan Society for the Promotion of Science (JSPS).

Poor sleep has been linked to dementia, but it is unclear whether unhealthy sleep habits contribute to the development of dementia or whether they are rather early symptoms of the disease. In a new study, researchers at Karolinska Institutet have investigated the link between sleep characteristics and how old the brain appears in relation to its chronological age.

The study includes 27,500 middle-aged and older people from the UK Biobank who underwent magnetic resonance imaging (MRI) of the brain. Using machine learning, the researchers estimated the biological age of the brain based on over a thousand brain MRI phenotypes.

Low-grade inflammation

The participants’ sleep quality was scored based on five self-reported factors: chronotype (being a morning/evening person), sleep duration, insomnia, snoring, and daytime sleepiness. They were then divided into three groups: healthy (≥4 points), intermediate (2-3 points), or poor (≤1 point) sleep.

“The gap between brain age and chronological age widened by about six months for every 1-point decrease in healthy sleep score,” explains Abigail Dove, researcher at the Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, who led the study. “People with poor sleep had brains that appeared on average one year older than their actual age.”

To understand how poor sleep can affect the brain, the researchers also examined levels of low-grade inflammation in the body. They found that inflammation could explain just over ten per cent of the link between poor sleep and older brain age.

“Our findings provide evidence that poor sleep may contribute to accelerated brain aging and point to inflammation as one of the underlying mechanisms,” says Abigail Dove. “Since sleep is modifiable, it may be possible to prevent accelerated brain aging and perhaps even cognitive decline through healthier sleep.”

Several possible explanations

Other possible mechanisms that could explain the association are negative effects on the brain’s waste clearance system, which is active mainly during sleep, or that poor sleep affects cardiovascular health, which in turn can have a negative impact on the brain.

Participants in the UK Biobank are healthier than the general UK population, which could limit the generalisability of the findings. Another limitation of the study is that the results are based on self-reported sleep.

The study was conducted in collaboration with researchers from the Swedish School of Sport and Health Sciences, and Tianjin Medical University and Sichuan University in China, among others. It was funded by the Alzheimer’s Foundation, the Dementia Foundation, the Swedish Research Council, the Loo and Hans Osterman Foundation for Medical Research, and the Knowledge Foundation. The researchers report no conflicts of interest.

Published on October 1 in Nature Astronomy, this discovery further strengthens the case for a dedicated European Space Agency (ESA) mission to orbit and land on Enceladus.

In 2005, Cassini found the first evidence that Enceladus has a hidden ocean beneath its icy surface. Jets of water burst from cracks close to the moon’s south pole, shooting ice grains into space. Smaller than grains of sand, some of the tiny pieces of ice fall back onto the moon’s surface, whilst others escape and form a ring around Saturn that traces Enceladus’s orbit.

Lead author Nozair Khawaja explains what we already knew: “Cassini was detecting samples from Enceladus all the time as it flew through Saturn’s E ring. We had already found many organic molecules in these ice grains, including precursors for amino acids.

The ice grains in the ring can be hundreds of years old. As they have aged, they may have been ‘weathered’ and therefore altered by intense space radiation. Scientists wanted to investigate fresh grains ejected much more recently to get a better idea of what exactly is going on in Enceladus’s ocean.

Fortunately, we already had the data. Back in 2008, Cassini flew straight through the icy spray. Pristine grains ejected only minutes before hit the spacecraft’s Cosmic Dust Analyzer (CDA) instrument at about 18 km/s. These were not only the freshest ice grains Cassini had ever detected, but also the fastest.

The speed mattered. Nozair explains why:

“The ice grains contain not just frozen water, but also other molecules, including organics. At lower impact speeds, the ice shatters, and the signal from clusters of water molecules can hide the signal from certain organic molecules. But when the ice grains hit CDA fast, water molecules don’t cluster, and we have a chance to see these previously hidden signals.”

It took years to build up knowledge from previous flybys and then apply it to decipher this data. But now, Nozair’s team has revealed what kind of molecules were present inside the fresh ice grains.

They saw that certain organic molecules that had already been found distributed in the E ring were also present in the fresh ice grains. This confirms that they are created within Enceladus’s ocean.

They also found totally new molecules that had never been seen before in ice grains from Enceladus. For the chemists reading, the newly detected molecular fragments included aliphatic, (hetero)cyclic ester/alkenes, ethers/ethyl and, tentatively, nitrogen- and oxygen-bearing compounds.

On Earth, these same molecules are involved in the chains of chemical reactions that ultimately lead to the more complex molecules that are essential for life.

“There are many possible pathways from the organic molecules we found in the Cassini data to potentially biologically relevant compounds, which enhances the likelihood that the moon is habitable,” says Nozair.

“There is much more in the data that we are currently exploring, so we are looking forward to finding out more in the near future.”

Co-author Frank Postberg adds: “These molecules we found in the freshly ejected material prove that the complex organic molecules Cassini detected in Saturn’s E ring are not just a product of long exposure to space, but are readily available in Enceladus’s ocean.”

Nicolas Altobelli, ESA Cassini project scientist adds: “It’s fantastic to see new discoveries emerging from Cassini data almost two decades after it was collected. It really showcases the long-term impact of our space missions. I look forward to comparing data from Cassini with data from ESA’s other missions to visit the icy moons of Saturn and Jupiter.”

Returning to Enceladus

Discoveries from Cassini are valuable for planning a future ESA mission dedicated to Enceladus. Studies for this ambitious mission have already begun. The plan is to fly through the jets and even land on the moon’s south polar terrain to collect samples.

A team of scientists and engineers is already considering the selection of modern scientific instruments that the spacecraft would carry. This latest result made using CDA will help guide that decision.

Enceladus ticks all the boxes to be a habitable environment that could support life: the presence of liquid water, a source of energy, a specific set of chemical elements and complex organic molecules. A mission that takes measurements directly from the moon’s surface, seeking out signs of life, would offer Europe a front seat in Solar System science.

“Even not finding life on Enceladus would be a huge discovery, because it raises serious questions about why life is not present in such an environment when the right conditions are there,” says Nozair.