Vascular Plants Had Extensively Colonized Land During Early Silurian, Finds Isotope Study

The colonization and expansion of plants on Earth is a defining milestone for the course of life on Earth. Terrestrial colonization has been attributed to a series of major innovations in plant body plans, anatomy and biochemistry that altered global geochemical cycles and climates.

It is critical to identify the beginning and track the expansion of those early land plants. However, the exact timing of land colonization by vascular plants remains controversial due to the variability of megafossils of early land plants, poor stratigraphic controls over their distribution, and associated uncertainties in molecular clock calculations.

Recently, scientists led by Professor Chen Daizhao of the Institute of Geology and Geophysics and Professor Feng Xinbin of the Institute of Geochemistry of the Chinese Academy of Sciences (CAS) used a mercury isotope to prove that vascular plants did indeed colonize the Earth on a large scale by the early Silurian period (about 444 million years ago). year). This work was published in Science advances On April 28th.

Researchers from Xishuangbanna Tropical Botanical Garden of the Chinese Academy of Sciences, Nanjing Institute of Geology and Paleontology of CAS, China Geological Survey and The Open University, UK, and College of Charleston, US, were also involved in the study.

Mercury (Hg) is the only heavy metal element that is liquid under normal conditions. It is also transported globally in the form of a gaseous element (Hg⁰) by atmospheric circulation. The most important realization about cycling in modern forests in recent decades is that mercury in vegetation is derived from mercury in the atmosphere.⁰ Assimilation through leaves rather than mercury precipitation or geological transport of mercury.

Terrestrial vegetation preferentially transports atmospheric mercury⁰which displays an independent segmentation of characteristic negative individual mass (odd-MIF, reported as Δ¹⁹⁹Hg) and even-MIF (reported as Δ²⁰⁰Hg) signatures, in terrestrial ecosystems. As land plants expanded and affected the weathering of terrestrial places, mercury contained these unique negative elements Δ¹⁹⁹Hg and Δ²⁰⁰The Hg values ​​will be carried over to nearshore marine environments, which initially showed significant positive signs. Therefore, the geological record of these isotopic systems likely provides a new tracer for tracking the colonization and expansion of plants on Earth.

In this study, the researchers used stable mercury isotope data from marine sediments spanning the Cambrian to Permian periods from different sedimentary fracies collected from southern China to highlight two episodes of distinct negative excursions at both odd and even MIF values ​​at the phase level in the Silurian and Carboniferous. .

They created a numerical model to quantify the worldly differences in the contribution of terrestrial organisms to the Paleozoic Era. They found that the findings push back in time the widespread spread of early vascular plants to 444 million years ago in the early Silurian period, at least in low-latitude regions such as southern China—a time period much older than the first known large fossils of a vascular plant.

The study linked the Paleozoic expansion of terrestrial organisms, particularly vascular plants, to the co-evolution of a range of Earth systems, particularly those of the atmosphere, oceans, weathering processes, and geochemical features.