Category: 7. Science

We present a near-infrared spectroscopic analysis (0.9-2.4 micron) of gravity indices for 57 ultracool dwarfs (spectral types M5.5 to L0), including exoplanet hosts TRAPPIST-1, SPECULOOS-2, SPECULOOS-3, and LHS 3154. Our dataset includes 61 spectra from the SpeX and FIRE spectrographs.

Using gravity-sensitive indices such as FeH absorption (at 0.99, 1.20, and 1.55 microns), the VO band at 1.06 microns, the H-band continuum, and alkali lines like K I (at 1.17 and 1.25 microns), we investigate correlations between surface gravity, stellar metallicity, and the presence of close-in transiting planets.

All four planet-hosting stars show intermediate-gravity spectral signatures despite indicators of field age. However, a volume-corrected logistic regression reveals no significant association between gravity class and planet occurrence. Among individual indices, FeH_z is the most promising tracer of planet-hosting status.

We tentatively identify a correlation between FeH_z (0.99 micron) and planet presence at the 2-sigma level, though this may reflect observational biases including transit probability, small-number statistics, and detection sensitivity. More robustly, we find a significant anti-correlation between FeH_z and metallicity ([Fe/H]) at 3.3 sigma. A Kruskal-Wallis test shows no significant metallicity difference across gravity classes, suggesting the observed FeH_z-metallicity trend is not driven by bulk metallicity differences.

We propose this anti-correlation reflects interplay between age, gravity, and composition: higher-metallicity objects may be systematically younger with lower gravities, suppressing FeH absorption. While our results only hint at a link between gravity-related characteristics and planet occurrence among late-M dwarfs, they underscore the need for caution when using spectral diagnostics to infer properties of planet-hosting ultracool dwarfs.

Fatemeh Davoudi, Benjamin V. Rackham, Julien de Wit, Jan Toomlaid, Michaël Gillon, Amaury H. M. J. Triaud, Adam J. Burgasser, Christopher A. Theissen

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2506.19928 [astro-ph.EP] (or arXiv:2506.19928v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2506.19928
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Submission history
From: Fatemeh Davoudi
[v1] Tue, 24 Jun 2025 18:05:48 UTC (2,086 KB)
https://arxiv.org/abs/2506.19928
Astrobiology

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Scientists are claiming a “cosmic chemistry breakthrough” following the discovery of a large “aromatic” molecule in deep space. The discovery suggests that these molecules could help seed planetary systems with carbon, supporting the development of molecules needed for life.

The molecule, called cyanocoronene, belongs to a class of carbon-based organic compounds called polycyclic aromatic hydrocarbons (PAHs), which are made up of multiple fused aromatic rings — structures in which electrons are shared across double-bonded carbon atoms, giving them unique chemical stability.

In these polar waters, cold, fresh surface water overlays warmer, saltier waters from the deep. In the winter, as the surface cools and sea ice forms, the density difference between water layers weakens, allowing these layers to mix and heat to be transported upward, melting the sea ice from below and limiting its growth.

Since the early 1980s, the surface of the Southern Ocean had been freshening, and stratification – that density difference between the water layers – had been strengthening. This was trapping heat below and sustaining more sea ice coverage.

Now, new satellite technology, combined with information from floating robotic devices which travel up and down the water column, shows this trend has reversed; surface salinity is increasing, stratification is weakening, and sea ice has reached multiple record lows – with large openings of open ocean in the sea ice (polynyas) returning.

This is the first time scientists have been able to monitor these changes in the Southern Ocean in real time. 

Aditya Narayanan, a postdoctoral research fellow at the University of Southampton and co-author on the paper, said: “While scientists expected that human-driven climate change would eventually lead to Antarctic Sea ice decline, the timing and nature of this shift remained uncertain.

“Previous projections emphasised enhanced surface freshening and stronger ocean stratification, which could have supported sustained sea ice cover. Instead, a rapid reduction in sea ice – an important reflector of solar radiation – has occurred, potentially accelerating global warming.”

What this all means is that – according to Professor Alberto Naveira Garabato, co-author on the study and Regius Professor of Ocean Sciences at the University of Southampton – our current understanding “may be insufficient” to accurately predict future changes.

“It makes the need for continuous satellite and in-situ monitoring all the more pressing, so we can better understand the drivers of recent and future shifts in the ice-ocean system.”

The paper – ‘Rising surface salinity and declining sea ice: a new Southern Ocean state revealed by satellites is published in Proceedings of the National Academy of Sciences and is available online.

This project has been supported by the European Space Agency.

Click here for more from the Oceanographic Newsroom.

Extreme environments impose strong mutation and selection pressures that drive distinctive, yet understudied, genomic adaptations in extremophiles.

In this study, we identify 15 bacterium–archaeon pairs that exhibit highly similar k-mer–based genomic signatures despite maximal taxonomic divergence, suggesting that shared environmental conditions can produce convergent, genome-wide patterns that transcend evolutionary distance. To uncover these patterns, we developed a computational pipeline to select a composite genome proxy assembled from non-contiguous subsequences of the genome.

Using supervised machine learning on a curated dataset of 693 extremophile microbial genomes, we found that 6-mers and 100 kbp genome proxy lengths provide the best balance between classification accuracy and computational efficiency. Our results provide conclusive evidence of the pervasive nature of k-mer–based patterns across the genome, and uncover the presence of taxonomic and environmental components that persist across all regions of the genome.

The 15 bacterium-archaeon pairs identified by our method as having similar genomic signatures were validated through multiple independent analyses, including 3-mer frequency profile comparisons, phenotypic trait similarity, and geographic co-occurrence data. These complementary validations confirmed that extreme environmental pressures can override traditionally recognized taxonomic components at the whole-genome level.

Together, these findings reveal that adaptation to extreme conditions can carry robust, taxonomic domain-spanning imprints on microbial genomes, offering new insight into the relationship between environmental mutagenesis and selection and genome-wide evolutionary convergence.

Life at the extremes: Maximally divergent microbes with similar genomic signatures linked to extreme environments, biorxiv.org

Astrobiology

The totality of bacteria, viruses and fungi that exist in and on a multicellular organism forms its natural microbiome. The interactions between the body and these microorganisms significantly influence both, the functions and health of the host organism. Researchers assume that the microbiome plays an important role in the defence against pathogens, among other things. The Collaborative Research Centre (CRC) 1182 “Origin and Function of Metaorganisms” at Kiel University has been investigating the highly complex interplay between host organisms and microorganisms for several years using various model organisms, including the nematode Caenorhabditis elegans.

In a recent study, researchers from the CRC 1182 have gained new insights into the molecular mechanisms within the microbiome which contribute to the defence against pathogens. In collaboration with scientists from the Max Planck Institute for Terrestrial Microbiology and the University of Edinburgh, they discovered that a protective bacterium of the genus Pseudomonas, which is found in the intestinal microbiome of C. elegans, produces sphingolipids. This result was surprising, as it was previously assumed that the production of sphingolipids was restricted to only a few bacterial phyla and the bacterial genus Pseudomonas was not known to be able to produce these specific molecules. The researchers discovered that Pseudomonas utilises an alternative metabolic pathway for sphingolipid production, which differs significantly from the known sphingolipid synthesis pathways in other bacteria. They were also able to show that the sphingolipids produced by Pseudomonas bacteria play an essential role in protecting the intestinal epithelium of the host from damage by the pathogen.

Responsible for sphingolipid production in Pseudomonas bacteria is a specific biosynthetic gene cluster that forms the enzymes for this novel metabolic pathway. Interestingly, similar gene clusters were also found in other host-associated gut bacteria, suggesting that the ability to produce sphingolipids may be more widespread than previously thought. This suggests that bacterial sphingolipids may play a central role in microbiome-mediated protection against infection – not only in C. elegans, but potentially also in other host organisms. The results of the interdisciplinary study, conducted under the leadership of PD Dr Katja Dierking (Evolutionary Ecology and Genetics research group at Kiel University), in collaboration with other research groups from Kiel and national and international cooperation partners, were recently published in the journal Nature Communications.

Bacteria use alternative pathway to produce protective sphingolipids

A few years ago, the Kiel research group had already published a study (Kissoyan et al. (2019), Current Biology) that showed that certain members of the C. elegans microbiota protect against pathogen infection.  “For one Pseudomonas species we knew that it can protect the worm from infections. However, we had not yet been able to identify the substances and mechanisms involved,” emphasises Dr Lena Peters, a scientist in the Evolutionary Ecology and Genetics research group.

In a broad-based collaboration of scientists both within the CRC 1182 – including Kiel professors Christoph Kaleta and Manuel Liebeke – and with external scientists, including Professor Helge Bode from the MPI for Terrestrial Microbiology in Marburg and Professor Dominic Campopiano from the University of Edinburgh in Scotland, the genetic and metabolic basis of the protection against infection mediated by the microbiome was analyzed. Using metabolic and transcriptional studies, single molecule analyses and mass spectrometry approaches, the researchers made a surprising discovery: they were able to prove that the protective bacteria of the genus Pseudomonas produce sphingolipids that influence the worm’s sphingolipid metabolism and thus support the host’s protection against pathogens.

“This finding is relatively new,” explains Peters, member of the CRC 1182, “normally, bacteria use the sphingolipid metabolism of host organisms to manipulate it in a targeted manner to promote infections. In our case, however, we observe the opposite – bacterial sphingolipids apparently actively support the protection of the host.” Sphingolipids are fat-like molecules that are typically found in eukaryotes, where they fulfil important structural and regulatory functions, but are rare in bacteria. In Pseudomonas, they are synthesised via a previously unknown, alternative metabolic pathway – not as a component of primary metabolism, as is usually the case, but as a so-called secondary metabolite.

The researchers discovered that this previously unknown metabolic pathway is based on a specific biosynthetic gene cluster, a so-called polyketide synthase. “With our experiments, we were able to confirm that the worms survived better in the presence of Pseudomonas fluorescens bacteria possessing this gene cluster when they were infected with the pathogen Bacillus thuringiensis,” emphasises Peters, first author of the study. After identifying the responsible genes, the scientists could confirm through further analyses that the gene cluster encodes the enzymes required for sphingolipid synthesis. “It is exciting to be authors on this important, breakthrough paper. We are pleased that our expertise in bacterial sphingolipid research has helped discover a new role in the worm microbiome for these enigmatic lipids,” says Prof. Campopiano.

“The protective mechanism against infections with B. thuringiensis apparently works indirectly. The lipids produced by Pseudomonas influence the worm’s sphingolipid metabolism, which presumably leads to an improved barrier function of the intestinal cells,” explains Peters. When the worm is infected with B. thuringiensis, the toxins of the pathogen create small pores in the cell membrane of the host, which makes it easier for the pathogens to penetrate. “We assume that the sphingolipid metabolism modified by P. fluorescens strengthens the stability and resistance of the cell membranes – and thus offers effective, indirect protection against pathogens,” Peters continues.

“Overall, the new research work expands our understanding of how microbial metabolites support host defence against pathogens,” says Dierking, independent group leader in the Evolutionary Ecology and Genetics research group. In the long term, the researchers of the CRC 1182, who are also active in Kiel University’s priority research area Kiel Life Science (KLS), hope that better knowledge of such fundamental mechanisms will also make it possible to influence disorders of the human gut microbiome which may result in better treatment options for a variety of associated diseases.

Reference: Peters L, Drechsler M, Herrera MA, et al. Polyketide synthase-derived sphingolipids mediate microbiota protection against a bacterial pathogen in C. elegans. Nat Commun. 2025;16(1):5151. doi: 10.1038/s41467-025-60234-1

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After nearly two decades in orbit, NASA’s Mars Reconnaissance Orbiter (MRO) is trying something new.

Engineers have taught the spacecraft how to roll – hard. This isn’t just a simple tilt. These are full-body rolls, sometimes nearly upside down.

The purpose is to see deeper beneath the surface of Mars and hunt for signs of water and ice.

Teaching Mars Orbiter to roll

The new technique comes from scientists at the Planetary Science Institute and NASA’s Jet Propulsion Laboratory.

Between 2023 and 2024, MRO performed three massive rotations – what the team calls “very large rolls” – to boost the performance of one of its key instruments.

“Not only can you teach an old spacecraft new tricks, you can open up entirely new regions of the subsurface to explore by doing so,” said Gareth Morgan of the Planetary Science Institute in Tucson, Arizona.

Advanced planning and careful balance

Mars Reconnaissance Orbiter was originally built to roll up to 30 degrees to aim its cameras and sensors at specific features on the Martian surface.

It’s a flexible platform, designed to twist and turn in space so scientists can target impact craters, landing zones, and more.

“We’re unique in that the entire spacecraft and its software are designed to let us roll all the time,” said Reid Thomas, MRO’s project manager at NASA’s Jet Propulsion Laboratory in Southern California.

But the bigger rolls – 120 degrees or more – are something else entirely. These require advanced planning and careful balance.

Mars Orbiter: Why every roll counts

MRO’s five main science instruments all have different needs. When one is pointed at Mars, others might lose their ideal view.

That means every maneuver is scheduled weeks in advance. Teams negotiate which instruments will be active and when.

An algorithm takes over from there, guiding the orbiter to roll and aim while keeping its solar panels locked on the Sun and its antenna aimed at Earth. For very large rolls, even those systems go dark temporarily.

“The very large rolls require a special analysis to make sure we’ll have enough power in our batteries to safely do the roll,” Thomas said.

Flipping for stronger radar returns

The massive rolls are especially helpful for SHARAD, the Shallow Radar instrument on board. It is designed to see about half a mile to 1.2 miles (0.8 – 1.9 kilometers) below the Martian surface.

SHARAD can also differentiate between ice, rock, and sand – a crucial capability for identifying water that future astronauts might one day use.

“The SHARAD instrument was designed for the near-subsurface, and there are select regions of Mars that are just out of reach for us,” said Morgan. “There is a lot to be gained by taking a closer look at those regions.”

Normally, SHARAD’s signals bounce off parts of the orbiter before hitting Mars, which muddies the data. But by flipping the spacecraft 120 degrees, SHARAD gets a clean line of sight. That single move boosts signal strength tenfold or more.

This improvement is big, but it comes with tradeoffs. During the maneuver, MRO can’t communicate with Earth or recharge its batteries. That limits the team to one or two very large rolls each year – for now.

Old instruments with new tricks

SHARAD isn’t the only instrument adjusting to new routines. The Mars Climate Sounder, a radiometer built at JPL, is also leaning into MRO’s roll capability. It tracks temperatures and atmospheric changes on Mars, revealing patterns in dust storms and cloud formations.

Originally, this instrument used a gimbal to adjust its view. But the gimbal started to fail in 2024. Now, the Climate Sounder depends on the orbiter’s roll maneuvering instead.

“Rolling used to restrict our science, but we’ve incorporated it into our routine planning, both for surface views and calibration,” said Mars Climate Sounder’s interim principal investigator, Armin Kleinboehl of JPL.

Mars Orbiter still delivers after 18 years

NASA’s Mars Reconnaissance Orbiter has been circling the Red Planet since 2006. It’s an aging but incredibly capable machine.

These new rolling maneuvers show that even after 18 years in space, it’s still finding new ways to contribute.

By shifting its body in bold new directions, MRO is helping us see what lies beneath the Martian dust – and just maybe, where water waits to be found.

Image Credit: NASA/JPL-Caltech

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Macquarie University research shows a chemical banned in Europe but still sprayed on Australian produce to kill fungus also wipes out beneficial insects and pollinators, potentially fuelling global insect decline.

A widely-used agricultural chemical sprayed on fruits and vegetables to prevent fungal disease is also killing beneficial insects that play a critical role in pollination and wider ecosystems.

New Macquarie University-led research published in Royal Society Open Science, shows chlorothalonil, one of the world’s most widely used agricultural fungicides, deeply impacts the reproduction and survival of insects, even at the lowest levels routinely found on food from cranberries to wine grapes.

“Even the very lowest concentration has a huge impact on the reproduction of the flies that we tested,” says lead author, PhD candidate Darshika Dissawa, from Macquarie’s School of Natural Sciences.

“This can have a big knock-on population impact over time because it affects both male and female fertility.”

The insect species Drosophila melanogaster, commonly called fruit fly or vinegar fly, was used as a laboratory model representing countless non-target insects found in agricultural environments.

“D. melanogaster is also at the bottom of the food chain, becoming food for a whole lot of other species,” says Dissawa.

Unlike major horticultural pests in Australia, such as the Queensland fruit fly (Bactrocera tryoni) and the Mediterranean fruit fly (Ceratitis capitata), D. melanogaster feed on rotting fruit and play an important role in nutrient recycling in agriculture.

Testing the fungicide

Scientists exposed D. melanogaster larvae to chlorothalonil amounts matching levels typically found in fruits and vegetables.

Even at the lowest dose tested, the flies showed a 37 per cent drop in egg production at their maturity, compared with unexposed individuals.

Supervising author Associate Professor Fleur Ponton, from Macquarie’s School of Natural Sciences, says the dramatic decline was surprising.

“We expected the effect to increase far more gradually with higher amounts. But we found that even a very small amount can have a strong negative effect,” Associate Professor Ponton says.

The findings add to mounting evidence of what researchers call the “insect apocalypse” – a global phenomenon that has seen insect populations plummet by more than 75 per cent in some regions in recent decades.

Where the fungicide is used

Although banned in the European Union, chlorothalonil is extensively applied to Australian crops to control fungal diseases such as mildews and leaf blights.

The chemical has been detected in soil and water bodies near agricultural areas, with residue levels in fruits and vegetables ranging from trace amounts to 460 milligrams per kilogram.

“Chlorothalonil is particularly common in orchards and vineyards and is often used preventatively when no disease is present,” Associate Professor Ponton explains.

“People assume fungicides like chlorothalonil only impact fungal diseases, but they can have devastating, unintended consequences for other species.” says Associate Professor Ponton.

Knock-on effect

The study found that chlorothalonil exposure during larval development caused severe reproductive damage in adult flies.

Females showed significantly reduced body weight, fewer egg-producing structures called ovarioles and drastically reduced egg production. Males had reduced iron levels, suggesting disruption to metabolic processes essential for sperm production.

The scientists also found the larvae consumed the contaminated food normally, ruling out taste aversion as an explanation.

“We didn’t find a significant aversion for food contaminated with chlorothalonil, except when there was a very high concentration of the chemical,” says Associate Professor Ponton. “This means the impacts are due to chlorothalonil ingestion.”

Knowledge gap has broad implications

In agricultural landscapes where entire orchards and vineyards are treated with fungicides, insects cannot escape chemically-contaminated food sources.

“We need bees and flies and other beneficial insects for pollination, and we think this is an important problem for pollinator populations,” Associate Professor Ponton says. “There is a strong commercial incentive to understand the impact in the field and address the use of this chemical.”

The research highlights a critical knowledge gap in pesticide regulation. Chlorothalonil is one of the most extensively used fungicides globally, but fewer than 25 scientific papers examine its effects on insects, despite mounting evidence of widespread insect population decline.

“People assume fungicide only affects fungal diseases, but it has an effect on other non-target organisms,” Associate Professor Ponton says.

The researchers have called for more sustainable agricultural practices, such as reduced frequency of applications to allow insect populations to recover between treatments.

“We need field trials to explore options and develop evidence-based guidelines to consider the knock-on effects of fungicides on beneficial insects,” says Associate Professor Ponton.

Future research will examine whether the reproductive damage carries over to subsequent generations and investigate the combined effects of multiple agricultural chemicals typically used together in farming operations.

 

Reference: Dissawa MD, Boyer I, Ponton F. Chlorothalonil exposure impacts larval development and adult reproductive performance in Drosophila melanogaster. Royal Soc Open Sci. 2025. doi: 10.1098/rsos.250136

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The Earth’s atmosphere is now trapping far more heat than climate models predicted. This energy imbalance has doubled since 2005, from 0.6 to 1.3 watts per square meter, according to researchers from Australia, France and Sweden. The Conversation reports.

Scientists believe the acceleration is due to the accumulation of greenhouse gases and changes in cloud cover. In particular, the area of white reflective clouds has decreased, while darker ones have increased. This weakens the planet’s ability to reflect the sun’s heat back into space.

Most of the additional energy (up to 90%) is absorbed by the oceans, but there is also melting of glaciers and warming of land. This accumulation of heat has already raised the average temperature of the Earth by 1.3–1.5°C compared to the pre-industrial period.

The authors emphasize that real changes are happening faster than the models predict. If the trend continues, the world could face increased heat waves, droughts and storms. What is particularly worrying is that only models with high sensitivity to emissions come close to the recorded values – they predict more severe warming in the future.

An additional threat is a possible reduction in funding for satellite climate monitoring in the United States, a key tool that allows us to capture such changes at an early stage.

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Ecosystems aren’t just defined by what species exist, but by how much life they contain. While scientists understand species diversity and where marine life is most abundant today, we still lack a clear picture of how biomass, the total weight of living organisms, has changed over time.

Biomass reveals the real impact and energy flow of life in an ecosystem, like knowing not just the cast of a play, but who the lead actors are and how powerful their performances can be. It’s a vital clue to understanding an ecosystem’s true strength and health across deep time.

While scientists have long known that biodiversity has increased throughout Earth’s history, a new Stanford study adds a key piece: biomass, or the total amount of ocean life, has also mostly grown over the last 500 million years.

Despite some dips during mass extinction events, the overall trend is upward, just like biodiversity. This suggests a powerful link: as life became more diverse, it also became more abundant, filling the oceans with both variety and volume.

Scientists uncover massive, diverse ecosystem deep beneath Earth’s surface

Imagine if ancient seas left behind a diary, not in words, but in shells and skeletons. That’s exactly what the team is decoding. Researchers studied thousands of rock samples packed with the fossilized remains of marine organisms, shells, algae, and tiny protists. These fossils recorded the biomass of their time, that is, the total “living material” preserved across Earth’s history.

Why does it matter?

Biomass reveals how much life an ecosystem could support, and how much energy it moves around, making it a key sign of past ocean health.

Although it once seemed too complex to measure across deep time, researchers took on the challenge. They analyzed over 7,700 limestone samples spanning 540 million years, using a method called petrographic point-counting to examine the amount of fossilized shell material.

By combining decades of studies with new data, they created a clearer picture of how life in Earth’s oceans has ebbed and flowed through deep history.

Some sea life could face extinction over the next century

They found that in the Cambrian Period, fewer than 10% of rocks had shell material. As life diversified during the Ordovician, that percentage rose, evidence of the Cambrian Explosion.

Calcifying sponges were among the early biomass leaders but were soon overtaken by echinoderms (like early starfish) and marine arthropods (like trilobites and crab ancestors).

Over the past 230 million years, oceans saw dramatic rises and falls in life, recorded in the shell content of marine rocks. Shell material stayed above 20%, signaling healthy ocean life, until the Late Devonian extinction (~375–360 million years ago) caused a notable drop.

Then came the worst: the Great Dying (~250 million years ago), the Permian-Triassic extinction, when shell content plunged to just 3%, reflecting a massive collapse in marine life.

Even after major extinctions like the end-Triassic and the one that ended the dinosaurs, marine life bounced back. In today’s era, the Cenozoic, shell remains now make up over 40% of marine rocks, largely due to mollusks and corals thriving.

To be sure, this rise reflected real increases in ocean life, not just fewer shell-destroying predators or sampling bias, researchers ran thorough tests. They analyzed fossil samples across shallow and deep waters, various latitudes, and different ancient continental setups.

Animal poop helps ecosystems adapt to climate change, study

The result? The trend held strong across the board, showing that the growth in shell content truly reflects a long-term rise in ocean biomass.

As ocean organisms became more specialized, they got better at using energy and nutrients, boosting ecosystem productivity. This efficient recycling from phytoplankton to decomposers helped support more life, reflected in greater biomass.

But today, human impacts like pollution, overfishing, and climate change threaten that balance. Scientists warn we may be entering a sixth mass extinction, where shrinking biodiversity could reduce biomass, and future fossil records might carry the traces of this decline.

Jonathan Payne, Dorrell William Kirby Professor of Earth and Planetary Sciences, said, “Our findings show that overall biomass is linked to biodiversity and that losses in biodiversity may suppress productivity for geologically meaningful intervals, adding one more argument for why conserving biodiversity is essential for the health of humans and our planet.”

Journal Reference:

1. Pulkit Singh, Jordan Ferré, Bridget Thrasher, et al. Macroevolutionary coupling of marine biomass and biodiversity across the Phanerozoic. Current Biology. DOI: 10.1016/j.cub.2025.06.006