Latest research suggests that the expansion of land plants approximately 455 million years ago triggered at least two near-extinction events for marine life, challenging previous timelines that placed significant plant expansion much later in the fossil record. The findings, published in multiple reports this week, indicate that the initial colonization of land by plants had a far more rapid and dramatic impact on global ocean conditions than previously understood.
Scientists at the University of Cincinnati, collaborating with researchers in China, re-evaluated the timing of early plant evolution using geochemical data and fossil evidence. Their analysis pushes back the date of substantial land plant development to the early Silurian period, roughly 455 million years ago – significantly earlier than many prior estimates. This earlier expansion coincides with geological evidence of major shifts in marine oxygen levels and biodiversity.
The primary mechanism linking plant life to marine disruption appears to be a massive increase in weathering of rocks on land. As plants spread their root systems, they accelerated the breakdown of silicate rocks, releasing vast quantities of nutrients into rivers and, the oceans. While nutrients can be beneficial, the scale of this influx triggered widespread algal blooms. The subsequent decay of these blooms consumed massive amounts of oxygen, creating hypoxic – or oxygen-depleted – zones in the oceans, suffocating marine life.
“We’ve known for some time that the evolution of land plants had a profound impact on Earth’s climate and ocean chemistry,” explained Michael Miller, a researcher at the University of Cincinnati involved in the study. “But this research demonstrates that this impact was both earlier and more severe than we previously thought.”
The research indicates that this process occurred in two distinct phases. The initial wave of plant expansion led to a significant, but not catastrophic, decline in marine biodiversity. A second, more substantial pulse of plant-driven weathering occurred later in the Silurian period, resulting in a more severe oxygen depletion event. The scale of these events is evidenced by changes in the marine fossil record, showing significant shifts in species composition and abundance.
As of 2023, over 242,000 marine species have been documented, with estimates suggesting potentially two million species remain undiscovered. The study highlights the vulnerability of marine ecosystems to terrestrial changes, a concern that remains relevant today given ongoing land-leverage changes and nutrient runoff from agriculture. The marine biome, covering approximately 70% of the Earth’s surface, is a complex network of habitats, including salt water and brackish water environments.
Researchers continue to investigate the specific mechanisms driving these ancient extinction events, and the long-term consequences for the evolution of marine life. Further study is planned to model the precise impact of weathering rates and nutrient delivery on ocean oxygen levels, and to refine the timeline of early plant evolution. No immediate institutional response to the findings has been issued.
