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A quantitative understanding of the nature and composition of low-mass rocky exo(planet) atmospheres during their evolution is needed to interpret observations.

The magma ocean stage of terrestrial- and sub-Neptune planets permits mass exchange between their interiors and atmospheres, during which the mass and speciation of the atmosphere is dictated by the planet’s volatile budget, chemical equilibria, and gas/fluid solubility in molten rock.

As the atmosphere cools, it is modified by gas-phase reactions and condensation. We combine these processes into an open-source Python package built using JAX called Atmodeller, and perform calculations for planet sizes and conditions analogous to TRAPPIST-1e and K2-18b.

For TRAPPIST-1e-like planets, our simulations indicate that CO-dominated atmospheres are prevalent during the magma ocean stage, which, upon isochemical cooling, predominantly evolve into CO₂-rich atmospheres of a few hundred bar at 280 K. Around 40% of our simulations predict the coexistence of liquid water, graphite, sulfur, and ammonium chloride-key ingredients for surface habitability.

For sub-Neptune gas dwarfs, pressures are sufficiently high (few GPa) to deviate the fugacities of gases from ideality, thereby drastically enhancing their solubilities. This buffers the total atmospheric pressure to lower values than for the ideal case. These effects conspire to produce CH₄-rich sub-Neptune atmospheres for total pressures exceeding around 3.5 GPa, provided H/C is approximately 100x solar and fO₂ moderately reducing (3 log10 units below the iron-wüstite buffer).

Otherwise, molecular hydrogen remains the predominant species at lower total pressures and/or higher H/C. For all planets at high temperature, solubility enriches C/H in the atmosphere relative to the initial composition.

Dan J. Bower, Maggie A. Thompson, Kaustubh Hakim, Meng Tian, Paolo A. Sossi

Comments: 41 pages, 10 figures in main text, 8 figures in appendices, submitted to ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.00499 [astro-ph.EP] (or arXiv:2507.00499v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.00499
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Submission history
From: Dan Bower
[v1] Tue, 1 Jul 2025 07:14:10 UTC (12,751 KB)
https://arxiv.org/abs/2507.00499
Astrobiology

In a first-of-its-kind study, Stanford researchers have measured how the abundance of ocean life has changed over the past half-billion years of Earth’s history.

Overall, the total mass of marine organisms has generally increased over the past 500 million years, the study showed, albeit with setbacks after major extinction events. The findings align with evidence for a similar rise in marine biodiversity – the total variety of organisms – over the past half-eon from studies dating as far back as the 19th century, suggesting an evolutionary connection between biomass and biodiversity. The research appears in Current Biology June 25.

“Understanding the amount of biomass is important because it represents key traits about an ecosystem that are not captured by the number of species or even the number of niches that they fill,” said study lead author Pulkit Singh, a postdoctoral scholar in Earth and Planetary Sciences in the Stanford Doerr School of Sustainability. “But as we move into the past, our measurements of biomass are very limited, so that was the big gap in biological history we wanted to fill with our study.”

The results come from an in-depth compilation and review of data from thousands of rock samples containing skeletal remains, which in the oceanic environment primarily comprise shells of animals, certain kinds of algae, and single-celled organisms called protists. Fossils with skeletal remains recorded the amount of biomass – the material comprising and produced by living things – that was preserved across different geological intervals. Biomass reveals the productivity of an ecosystem, indicating the amount of energy (food) present and the quantity of organisms that a system can support. Productivity, in turn, speaks to ecosystem health, and in the broad aggregate, to planetary health.

Researchers have long shied away from attempting to measure biomass, given the immense effort required to gather relevant data and the possibility that data wouldn’t be sufficient for revealing meaningful patterns. Singh undertook the challenge, devoting several years to compiling data published over decades, as well as adding new data from his own samples.

“The first quantitative effort to document and graph biodiversity across geological time was made in 1860, but until Pulkit’s paper, there’s never been a corresponding biomass-across-time paper,” said senior study author Jonathan Payne, the Dorrell William Kirby Professor of Earth and Planetary Sciences at Stanford. “I’m impressed by his intellectual courage to go and take a chance on a project like this.”

Picking through the past

For the study, Singh and colleagues considered more than 7,700 marine limestone samples from all over the world spanning the past 540 million years that have been documented across more than 100 scientific studies. The research team relied on data gathered via a standard method known as petrographic point-counting to assess the percentage of each sample that contained skeletal remains. The time-consuming technique involves cutting and polishing rocks very thinly so light can shine through them, then examining the thin sections of rock samples under a microscope to quantify their composition.

During the Cambrian, the earliest period sampled that started about 540 million years ago, researchers found fewer than 10 percent of the rocks, on average, were composed of shell material. As the Cambrian gave way to the Ordovician Period about 485 million years ago, that percentage climbed, partly reflecting the “Cambrian Explosion,” when life on Earth dramatically expanded in diversity and complexity. Calcifying sponges were initially notable contributors to biomass but were later leapfrogged by newly evolved echinoderms – including ancestors of modern-day starfish – and marine arthropods, including extinct trilobites and ancestors of crabs.

Throughout much of the next 230 million years, shell content soared well above 20 percent, with a significant decrease during one of the “Big Five” mass extinction events in the Late Devonian, about 375 to 360 million years ago. The biggest drop in living history then struck about 250 million years ago during the “Great Dying,” the Permian-Triassic extinction, when shell percentage plummeted to about 3 percent.

Life recovered, and except for subsequent significant mass extinctions – the end-Triassic extinction about 200 million years ago and the Cretaceous-Paleogene about 66 million years ago, which infamously killed off the non-avian dinosaurs – biomass has boomed in our current geological era, the Cenozoic, with shells exceeding 40 percent of rock volume, thanks in part to substantial contributions from mollusks and corals. “The overall pattern that we were able to capture is that it’s a gradual increase,” Singh said.

One of the biggest challenges in conducting the study involved telling whether the increasing shell content in rocks truly signaled a rise in bio-abundances over time or if other ecological factors, such as a decrease in shell-boring and -destroying predators, or methodological sample biases were behind the pattern.

To cross-check their results, the researchers performed a series of rigorous tests. They sorted samples by depositional environment of shallow or deep water, factoring in how shell remains accumulate more frequently in better-populated shallow waters. The researchers also sorted samples by different latitudes and locations and shapes of the predecessors of today’s continents. Through it all, the signal remained strongly consistent across water depths, latitudes, and geologic settings.

“The more tests we did and the more we divided our dataset, we realized that these big biological patterns we were seeing stayed over time,” Singh said.

Life-altering events

As to why marine life has generally increased, evidence points to the parallel trends in greater diversity. With marine organisms becoming more specialized and more variable in their specializations, more energy can be extracted from available nutrients and food resources. This enhanced nutrient recycling starts with the autotrophs, such as phytoplankton, that photosynthetically “feed” on sunlight and ends with decomposers returning nutrients to the environment that autotrophs take up.

“The overall idea is that there is more food available in ecosystems and because of that, the ecosystems can support more life, there’s more energy available, and that leads to greater abundance expressed in biomass,” Singh said.

Whether or not the plenitude seen over the last hundreds of millions of years will persist could be in question, considering impacts from human activities. Although people have caused fertilizer runoff, overfishing, ocean acidification, and more during a mere blip in geological time, scientists have widely documented an ongoing, human-driven sixth mass extinction. Accumulating losses in biodiversity could potentially reduce biomass, and vice versa – a signal that perhaps could be captured in the fossil record currently being laid down.

“From our study’s perspective, modern times are quite complicated given the extent of human activity that’s rapidly altering conditions planetwide, including in the oceans,” said Payne, who is also a senior fellow at the Stanford Woods Institute for the Environment. “But 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 of why conserving biodiversity is essential for the health of humans and our planet.”

Additional Stanford co-authors include Jordan Ferré, Bridget Thrasher, and Pedro Monarrez. Other study co-authors are from the Virginia Polytechnic Institute and State University, King Fahd University of Petroleum and Minerals, Cantrell GeoLogic LLC, Trinity University, and the University of Ferrara. The research was supported by a Frontier Research in Earth Sciences grant from the U.S. National Science Foundation.

Macroevolutionary coupling of marine biomass and biodiversity across the Phanerozoic, Current Biology

Astrobiology,

We present the results of astrochemical modeling of complex organic molecules (COMs) in the ice and gas of the prestellar core L1544 with the recently updated MONACO rate equations-based model.

The model includes, in particular, non-diffusive processes, new laboratory verified chemical routes for acetaldehyde and methane ice formation and variation of H and H₂ desorption energies depending on the surface coverage by H₂ molecules.

For the first time, we simultaneously reproduce the abundances of several oxygen-bearing COMs in the gas phase, the approximate location of the peak of methanol emission, as well as the abundance of methanol in the icy mantles of L1544.

Radical-radical reactions on grains surface between species such as CH₃, CH₃O and HCO efficiently proceed non-diffusively. COMs are delivered to the gas phase via chemical desorption amplified by the loops of H-addition/abstraction surface reactions.

However, gas-phase chemical reactions as well provide a noticeable input to the formation of COMs in the gas, but not to the COMs solid-state abundances. This particularly applies for CH₃CHO and CH₃OCH₃. The simulated abundances of COMs in the ice are in the range 1%–2% (for methyl formate ice) or ∼~0.1% (for CH₃CHO and CH₃OCH₃) with respect to the abundance of H₂O ice.

We stress a similarity between the simulated abundances of icy COMs in L1544 and the abundances of COMs in the gas phase of hot cores/corinos. We compare our non-diffusive model with the diffusive model and provide constraints for the species’ diffusion-to-desorption energy ratios.

Katerina Borshcheva (1 and 2), Gleb Fedoseev (3, 4 and 1), Anna F. Punanova (5), Paola Caselli (6), Izaskun Jiménez-Serra (7), Anton I. Vasyunin (1) ((1) Research Laboratory for Astrochemistry, Ural Federal University, Yekaterinburg, Russia (2) Institute of Astronomy of the Russian Academy of Sciences, Moscow, Russia (3) Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, China (4) Xinjiang Key Laboratory of Radio Astrophysics, Urumqi, China (5) Onsala Space Observatory, Råö, Onsala, Sweden (6) Max-Planck-Institute for Extraterrestrial Physics, Garching, Germany (7) Centro de Astrobiologia (CSIC-INTA), Torrejon de Ardoz Madrid, Spain)

Comments: 34 pages, 13 figures, 10 tables, accepted to The Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2507.00338 [astro-ph.GA] (or arXiv:2507.00338v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2507.00338
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Submission history
From: Anton Vasyunin
[v1] Tue, 1 Jul 2025 00:35:09 UTC (629 KB)
https://arxiv.org/abs/2507.00338
Astrobiology