BEIJING, Feb. 25 (Xinhua) — Land plants began colonizing continents and shaping Earth’s surface environment much earlier than previously thought, a study led by Chinese scientists shows.

The study, led by researcher Zhao Mingyu from the Institute of Geology and Geophysics at the Chinese Academy of Sciences (CAS), provides new geochemical evidence that early plants expanded extensively on land between 455 and 445 million years ago, pushing the timeline back by more than 20 million years than the previous view of about 420 million years ago.

Zhao’s team collaborated with 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 at CAS. The findings were published Tuesday in the journal Nature Ecology & Evolution.

Determining exactly when plants first spread over land and began influencing Earth’s systems is a central question in understanding Earth’s evolution.

The research team used a new geochemical approach to track the plant’s expansion. The organic matter produced by land plants has a significantly higher ratio of organic carbon to phosphorus compared to the organic matter produced by marine organisms, the researchers explained. As plants spread across the continent, photosynthesis on land was enhanced and the production of land-based organic matter increased.

This material was transported to the ocean by rivers and eventually buried in seafloor sediments, where the ratio of organic carbon to phosphorus increased. Since the production of land-derived organic carbon is closely related to burial in the ocean, this proportion of marine mud deposits serves as a reliable tracking measure for tracking plant activity on land.

By systematically analyzing marine sediment records under different oxidizing conditions, the researchers found that the ratio of organic carbon to phosphorus began to rise sharply about 455 million years ago.

After evaluating multiple potential controlling factors, the researchers concluded that this surge reflects a large increase in land plant productivity.

Further modeling estimates suggest that since the Late Ordovician period (about 455 million years ago), land-based organic carbon has accounted for about 42 percent of the total organic carbon buried in marine sediments, a figure approaching modern-day levels of 30 to 57 percent.

Continental-scale analyzes indicate that plant expansion may have first occurred on the ancient Laurentian continent, which now forms most 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.

According to the research team, these findings suggest that the emergence of early land plants approximately 455 million years ago significantly accelerated the oxidation of the Earth’s surface environment, which may have contributed to the late Ordovician ice age and mass extinction. ■