Through research, the Institute of Geology and Geophysics of the Chinese Academy of Sciences discovered new geochemical evidence indicating thatLand plants began shaping Earth's surface environment earlier than previously thought. There are significant differences in the organic matter produced by land plants and marine primary producers, with organic matter formed by land plants having a higher organic carbon/phosphorus ratio.
As land plants expanded across the continent, terrestrial photosynthesis increased and the production of terrestrial organic matter increased accordingly.
This terrestrial-derived organic matter is transported to the ocean via rivers and eventually enters marine sediments, increasing the organic carbon/phosphorus ratio in marine sediments.
Since the production of terrestrial organic carbon is closely coupled with its burial process in the ocean, the organic carbon/phosphorus ratio in marine clastic sediments has become an important indicator for tracking the input of terrestrial organic carbon and even reflecting changes in terrestrial net primary productivity.
The research team conducted a systematic analysis of marine clastic sedimentation records under different redox conditions and found that the organic carbon/phosphorus ratio has increased significantly since about 455 million years ago.
An evaluation of multiple possible controls suggests that this change reflects a significant increase in terrestrial net primary productivity associated with early land plant expansion.
The mixed model estimation results further show thatSince the Late Ordovician (about 455 million years ago), terrestrial organic carbon has accounted for approximately 42±15% of the total organic carbon buried in marine sediments, which is close to modern levels (30%–57%).
Analyzes at the ancient continental scale also show thatThe expansion of land plants may have first occurred in Laurentia (a major location such as present-day North America).
The study also revealed that the organic carbon/phosphorus ratio increased significantly twice during the Late Ordovician, corresponding to two important carbon isotope anomalies that occurred during this period.
This indicates that the input of carbon-rich, phosphorus-poor terrestrial organic matter into marine sediments promotes the burial of global organic carbon, thereby promoting the accumulation of atmospheric oxygen content and reducing carbon dioxide concentration.
In addition, enhanced silicate and phosphorus weathering triggered by rapid expansion of land plants may further amplify these environmental effects.
Taken together,The rise of early land plants may have significantly promoted the oxidation process of the earth's surface environment about 455 million years ago, and may have contributed to the occurrence of the Late Ordovician glaciation and mass extinction events.
▲Simulation diagram of early plant expansion on land