BEIJING, Feb. 25 (Xinhua) -- Land plants began colonizing the continents and shaping Earth's surface environment much earlier than previously thought, a study led by Chinese scientists showed.
The research, led by researcher Zhao Mingyu at the Institute of Geology and Geophysics under the Chinese Academy of Sciences (CAS), provides fresh geochemical evidence that early plants expanded massively on land between 455 million and 445 million years ago -- pushing back the timeline by more than 20 million years from the traditional view of around 420 million years ago.
Zhao's team collaborated with the scientists from Yale University, the University of Exeter, the University of Leeds, the University of Science and Technology of China, and the Institute of Vertebrate Paleontology and Paleoanthropology of the CAS. The findings were published on Tuesday in the journal Nature Ecology & Evolution.
Determining exactly when plants first spread across land and began influencing Earth's systems has been a central question in understanding the planet's evolution.
The research team used a novel geochemical approach to track plant expansion. Organic matter produced by land plants has a significantly higher ratio of organic carbon to phosphorus compared to that from marine organisms, the researchers explained. As plants spread across continents, photosynthesis on land intensified, increasing the production of land-derived organic material.
This material was carried by rivers into the oceans and eventually buried in seafloor sediments, raising the organic carbon-to-phosphorus ratio there. Because the production of land-sourced organic carbon is tightly linked to its burial in the ocean, this ratio in marine mud deposits serves as a reliable tracer for tracking plant activity on land.
By systematically analyzing marine sediment records from different oxidation conditions, the team found that the organic carbon-to-phosphorus ratio began rising sharply around 455 million years ago.
After evaluating multiple potential controlling factors, the researchers concluded that this spike reflected a major increase in land-based plant productivity.
Further modeling estimates suggest that since the Late Ordovician period (around 455 million years ago), land-sourced organic carbon has accounted for about 42 percent of total organic carbon buried in ocean sediments -- a figure approaching modern levels of 30 to 57 percent.
Continental-scale analysis indicates plant expansion may have first occurred on the ancient continent of Laurentia, which now forms much of North America.
The study also found that the organic carbon-to-phosphorus ratio rose sharply twice during the Late Ordovician, coinciding with two major carbon isotope excursion events.
Taken together, the findings suggest that the rise of early land plants significantly advanced the oxidation of Earth's surface environment around 455 million years ago, and may have contributed to the Late Ordovician ice age and mass extinction events, according to the research team. ■
