In a landmark study poised to reshape our understanding of Earth’s deep past, researchers have employed advanced earth system simulations to reveal a Proterozoic ocean fundamentally different from today’s seas—characterized as greener yet notably less biologically productive. This novel insight challenges longstanding assumptions about oceanic conditions during the Proterozoic Eon, a geological interval vital to the evolution of complex life but often shrouded in scientific uncertainty due to sparse direct fossil evidence.
The Proterozoic Eon, extending roughly from 2.5 billion to 541 million years ago, witnessed pivotal events including the rise of atmospheric oxygen and the emergence of early eukaryotic life forms. Yet, the nature and productivity of the oceans during this time have remained enigmatic, with most previous models suggesting relatively modest biological activity compared to later Phanerozoic oceans. The new research, led by Liu, P., Liu, Y., and Dong, L., leverages cutting-edge earth system simulations to reconstruct ocean chemistry, climate interactions, and photosynthetic activity during this critical period.
Central to the study is the use of sophisticated biogeochemical models integrated within comprehensive climate simulations, designed to track nutrient cycles, trace element distributions, and photosynthetic pigment concentrations. These factors together influence oceanic “greenness,” a proxy for phytoplankton biomass and photosynthetic efficiency. The simulation outcomes indicate elevated concentrations of green-pigmented cyanobacteria and other photosynthetic organisms, which imparted a distinctive greenish tint to Proterozoic seas. This observation marks a clear departure from the more familiar blue hue dominated by modern marine phytoplankton, mostly rich in chlorophyll-a.
However, despite the perceived greenness, the simulations also reveal a paradox: lower overall primary productivity compared to later geological intervals. This discrepancy stems largely from nutrient limitations, particularly lower phosphorus availability, and constraints imposed by ocean chemistry during the Proterozoic. The research intricately dissects how reduced nutrient recycling, different redox conditions, and expanded oxygen minimum zones confined biologically productive niches, inhibiting widespread primary production despite abundant light and favorable temperatures.
A major driver behind the greener appearance was an ecosystem dominated by a particular suite of photosynthetic microbes adapted to the unique chemical milieu of ancient oceans. Unlike the complex phytoplankton communities found today—which include diatoms and coccolithophores—Proterozoic phytoplankton were primarily oxygenic photosynthesizers with pigments tuning their spectral absorption toward green wavelengths. This evolutionary adaptation likely responded to elevated iron concentrations and altered light penetration profiles under anoxic to suboxic ocean conditions.
This research revisits classic interpretations of Proterozoic ocean oxygenation events and the implications for biogeochemical cycling. Previous hypotheses posited a sluggish, oxygen-poor world with limited biospheric productivity. However, the integrated simulations suggest that while oxygen levels remained low relative to modern standards, localized zones exhibited transient oxygenation linked to bursts of microbial photosynthetic activity. These oxygen oases may have acted as crucibles for early eukaryotic diversification, setting the stage for the eventual Cambrian explosion.
Beyond biological implications, the findings also hold significance for reconstructing ancient climate regimes. The greening of oceans is tied to feedback mechanisms affecting atmospheric composition, particularly greenhouse gases such as methane and carbon dioxide. The lower productivity implies reduced carbon sequestration via the biological pump, potentially modulating global temperatures and contributing to the distinctive climate fluctuations characteristic of the Proterozoic.
The research team employed a multi-disciplinary approach integrating paleoenvironmental geochemistry, microbial ecology, and state-of-the-art computational modeling. By calibrating their models against geochemical proxies such as isotopic records of carbon, sulfur, and iron, they achieved unprecedented resolution in simulating the interplay between ocean chemistry and biological processes. This methodological advancement paves the way for revisiting other ambiguous periods in Earth’s history with a fine-grained lens.
Importantly, the implications of this study extend beyond paleontology or ancient oceanography. The findings provide a conceptual framework for understanding how microbial ecosystems respond to variations in nutrient availability and redox states—a topic with direct relevance to modern-day ocean deoxygenation and the health of marine food webs amidst climate change. The analogy between ancient Proterozoic conditions and contemporary hypoxic zones offers a powerful reminder of the ocean’s delicate balance and vulnerability.
Controversially, the study challenges entrenched views that equate oceanic green coloration strictly with high productivity. Instead, the Proterozoic ocean serves as a natural laboratory illustrating how pigment adaptations and nutrient dynamics can decouple color signals from ecosystem function. This recalibration urges caution in using remote sensing techniques for paleoproductivity estimates without considering pigment ecology and biochemical constraints.
Additionally, by tracing the evolutionary trajectories of early photosynthetic microbes, the research sheds light on the ecological strategies pre-dating the rise of eukaryotic algae. The dominance of green-pigmented cyanobacteria underscores a simpler but ecologically significant biosphere, one that shaped the biogeochemical canvas upon which complex life later flourished. This adds nuance to the narrative of life’s ascent, suggesting a mosaic rather than a linear progression.
The notion of a less productive yet greener Proterozoic ocean also has ramifications for interpreting sedimentary records, specifically the accumulation of organic carbon and banded iron formations. The simulations indicate that lower primary production constrained organic carbon burial rates, influencing atmospheric oxygen levels and thus Earth’s oxidation trajectory over geological time. This feedback between productivity and atmospheric chemistry is pivotal in understanding Earth system evolution.
Furthermore, the greening trend aligns with mounting evidence from ancient stromatolite and microbial mat fossils, which provide morphological correlates for dominant phototrophic communities in Proterozoic shallow marine settings. These biological structures likely contributed to reef-building processes and sediment stabilization in ways distinct from later coral-dominated systems, highlighting an alternative ecosystem engineering paradigm.
The data and insights reveal a dynamic, heterogeneous ocean environment richly textured across spatial and temporal scales. Oxygen and nutrient gradients fostered patchy productivity hotspots interspersed with vast, less active regions. Such ecological heterogeneity would have created diverse microhabitats essential for evolutionary experimentation and the eventual rise of more complex multicellular organisms.
Looking forward, the study establishes a robust platform for future investigations into the links between ocean redox states, primary productivity, and climate during Earth’s formative eons. Enhanced modeling capabilities, combined with burgeoning fossil discoveries and geochemical proxies, will refine our ability to reconstruct ancient biospheres with ever greater fidelity. This interdisciplinary synergy revitalizes Proterozoic research, underscoring its relevance for understanding planetary habitability.
In summation, Liu, P., Liu, Y., Dong, L., and colleagues have fundamentally revised how we envisage the Proterozoic ocean. Their evidence for a greener yet less productive marine environment invites a reevaluation of early Earth’s biosphere and its environmental controls. These findings bridge gaps between geology, biology, and climate science, charting a compelling narrative of life’s intricate dance with the planet’s evolving chemistry.
As the field advances, this seminal work will likely catalyze renewed interest and debate regarding ocean productivity patterns and their role in Earth system dynamics through deep time. Such knowledge not only enriches our grasp of Earth history but also equips humanity with perspective on the fragility and adaptability of ocean ecosystems—lessons vital as we confront accelerating environmental change today.
Subject of Research: Proterozoic ocean chemistry, photosynthetic ecosystem composition, and primary productivity using earth system simulations.
Article Title: Earth system simulations suggest that the Proterozoic ocean was greener but less productive.
Article References:
Liu, P., Liu, Y., Dong, L., et al. Earth system simulations suggest that the Proterozoic ocean was greener but less productive. Nat Commun (2026). https://doi.org/10.1038/s41467-026-69654-z
Image Credits: AI Generated
