Scientists have uncovered compelling evidence that land plants began transforming Earth’s surface environments roughly 455 million years ago, far earlier than previously estimated.
The findings, published February 24 in Nature Ecology & Evolution, point to the Late Ordovician period as a pivotal turning point in Earth’s climate and oxygen history.
The research team was led by Prof. Zhao Mingyu at the Institute of Geology and Geophysics of the Chinese Academy of Sciences. According to the team, early terrestrial plants played a far greater role in shaping global systems than previously understood.
“Land plants fundamentally changed how carbon and nutrients moved through the Earth system,” the researchers state in the study, emphasizing that their expansion triggered cascading environmental effects.
To trace the earliest influence of land plants, the team analyzed marine siliciclastic sediment records deposited under varying ocean redox conditions. They focused on organic carbon-to-total phosphorus ratios (Corg/Ptotal), a powerful geochemical proxy that reveals how much carbon-rich material entered the oceans from land.
Unlike marine primary producers, land plants generate organic matter with significantly higher carbon-to-phosphorus ratios. As terrestrial vegetation expanded, it increased photosynthesis on land, producing more organic material. Rivers and runoff transported this carbon-rich, phosphorus-poor matter into the oceans, where it was buried in marine sediments.
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The researchers detected a marked rise in Corg/Ptotal ratios beginning around 455 million years ago. After evaluating alternative explanations, they concluded that the most plausible driver was a sharp increase in terrestrial net primary productivity fueled by the spread of early land plants.
“Our data show a pronounced geochemical shift that aligns with intensified terrestrial carbon production,” the team explains, linking sediment chemistry directly to biological innovation on land.
Using mixing models, the researchers estimated that since the Late Ordovician, terrestrial organic carbon has accounted for roughly 42 ± 15 percent of total organic carbon buried in marine sediments. That figure closely resembles modern values, which range between 30 and 57 percent.
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Such findings suggest that land ecosystems were already playing a role comparable to today’s carbon cycle contributions nearly half a billion years ago.
Further paleocontinental analysis indicates that plant expansion may have begun earlier on the Laurentian continent. It offers new insight into how geography influenced early terrestrial colonization.
The study also identifies two distinct spikes in the Corg/Ptotal ratios. It coincides with major carbon-isotopic excursions during the Late Ordovician. This alignment suggests that increased burial of carbon-rich organic matter altered atmospheric composition.
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When organic carbon is buried in sediments rather than decomposed, it effectively removes carbon dioxide from the atmosphere while allowing oxygen levels to rise. According to the researchers, intensified burial during this period likely promoted atmospheric oxygen accumulation and reduced CO₂ concentrations.
At the same time, the rapid colonization of land by plants would have accelerated silicate and phosphorus weathering processes. These chemical reactions further draw down carbon dioxide, amplifying cooling trends.
Together, these mechanisms may have contributed to the Late Ordovician glaciation. This is one of the earliest major ice ages in Earth’s history.
“The expansion of land plants likely played a central role in driving surface oxygenation and climatic shifts,” the study notes, suggesting that biological innovation directly influenced planetary-scale processes.
The Late Ordovician period also witnessed one of the first major mass extinction events. While multiple factors were involved, the new research indicates that plant-driven climate cooling and changes in ocean chemistry may have indirectly shaped the conditions that led to widespread marine losses.
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By reshaping nutrient cycles, atmospheric composition, and global temperatures, early plants may have set off feedback loops that reverberated throughout Earth’s systems.
The study was conducted in collaboration with scientists from Yale University, the University of Exeter, the University of Leeds, the University of Science and Technology of China, and the CAS Institute of Vertebrate Palaeontology and Palaeoanthropology.
As scientists continue to refine the timeline of terrestrial colonization, the findings indicate that long before forests dominated continents, the earliest land plants were already reshaping Earth’s climate, chemistry, and habitability.
