The Cambrian Explosion of Life is the most milestone event in the history of life evolution: within just tens of millions of years, the ancestors of living animal species emerged in stages, mineralized bones rapidly spread, and the complex marine ecosystem centered around multicellular animals was officially laid. However, the climate and environmental background that drove this life "fast forward" has always been shrouded in fog, with the concentration of atmospheric carbon dioxide (CO2) being a long-standing and unresolved key puzzle. CO2 is a core factor in regulating global climate, profoundly affecting surface temperature, seawater acidity and alkalinity, and continental weathering intensity. However, previous reconstruction of CO2 concentration during this period relied almost entirely on carbon cycle model deduction, with significant differences in results between different schemes and a lack of direct geological evidence constraints. Recently, Professor Chang Chao and Professor Zhang Xingliang from the Early Life and Environment Research Team at Northwestern University, together with a research team composed of scientists from the United States, Russia, and other countries, quantitatively reconstructed the atmospheric carbon dioxide concentration and climate change during the entire process of the Cambrian Explosion based on fossil organic carbon isotope records. The research team collected macroalgae fossils from eight classic fossil biota in China and Russia, covering the period from the late Ediacaran to the mid Cambrian (approximately 553-508 million years ago), and fully spanning the entire process of the Cambrian Explosion. These algae preserved in the form of carbonaceous films were the core contributors to the primary productivity of the ocean at that time; The organic carbon isotope composition (δ 13C) in its body faithfully records the carbon isotope fractionation effect during photosynthesis, and the fractionation intensity is directly related to the dissolved CO2 concentration in seawater. It is precisely with the help of this principle that the team inverted the concentration of atmospheric CO2 during the Cambrian Explosion period by testing the carbon isotope signals of fossil algae.

The reconstruction results indicate that the global climate during the Cambrian Explosion experienced a three-stage change process from greenhouse to super greenhouse and back to greenhouse: between 553 million and 529 million years ago, atmospheric CO2 concentration rapidly increased from about 6 times modern levels to about 14 times, and the Earth entered an extreme super greenhouse period;

; After 529 million years ago, the concentration of CO2 continued to decline, dropping to about five times the modern level by 508 million years ago, and the climate returned to a greenhouse state (Figure 1). At the same time, the research team also conducted carbon strontium isotope coupling analysis, and the results showed that the changes in atmospheric carbon dioxide concentration were highly coupled with the evolution of strontium isotopes (87Sr/86Sr) in seawater during the same period: the stage of rapid increase in CO2 corresponded to a significant decrease in the strontium isotope ratio in seawater.

The remote regulation of surface systems by deep Earth processes has profoundly shaped the climatic conditions and rhythms of Cambrian life evolution. The high temperature during the super greenhouse stage can suppress vertical mixing and thermal circulation in the ocean, promote the expansion of hypoxic water bodies, and provide a unique ecological niche for early animal groups with low oxygen tolerance; Subsequently, the climate returned to a mild greenhouse period, and the saturation of seawater carbonate gradually increased, creating favorable conditions for the popularization of mineralized animal bones and the radiation evolution of shell bearing organisms.

This achievement is a paradigm for the in-depth interdisciplinary study of the co evolution of structure environment life, geochemistry, and paleontology. Using solid fossils as carriers to solve the problem of reconstructing ancient climate, the causal chain between tectonic activity, climate change, and life evolution is linked through the synergistic evolution law of carbon and strontium isotopes. Although there is still some uncertainty in the absolute value of reconstructed carbon dioxide concentration, this is the first time in academia that the atmospheric CO2 concentration and climate change framework of the entire Cambrian Explosion process have been fully outlined based on physical geological records. It opens up a new research perspective for understanding how deep processes and surface systems of the Earth jointly write a magnificent chapter in the evolution of life.

Article information: Chang, C., Zhao, M., Ju, P. et al. Algal δ13C reveals climate changes during the Cambrian Explosion. Nat Commun (2026). https://doi.org/10.1038/s41467-026-74516-9.