The impacts of land plant evolution on Earth's climate and oxygenation state ? An interdisciplinary review

The Paleozoic emergence of terrestrial plants has been linked to a stepwise increase in Earth's O2 levels and a cooling of Earth's climate by drawdown of atmospheric CO2. Vegetation affects the Earth's O2 and CO2 levels in multiple ways, including preferential organic carbon preservation by decay-resistant biopolymers (e.g. lignin) and changing the continental weathering regime that governs oceanic nutrient supply and marine biological production. Over shorter time scales (≤1 Myr), land plant evolution is hypothesized to have occasionally enhanced P weathering and fertilized the oceans, expanding marine anoxia and causing marine extinctions. Oceanic anoxia would eventually become limited by oceanic O2 uptake as oxygen accumulates in the atmosphere and surface oceans when excess organic carbon is buried in marine sediments. Here, we review hypotheses and evidence for how the evolving terrestrial ecosystems impacted atmospheric and oceanic O2 and CO2 from the Ordovician and into the Carboniferous (485–298.9 Ma). Five major ecological stages in the terrestrial realm occurred during the prolonged time interval when land was colonized by plants, animals and fungi, marked by the evolution of 1) non-vascular plants, 2) vascular plants with lignified tissue, 3) plants with shallow roots, 4) arborescent and perennial vegetation with deep and complex root systems, and 5) seed plants. The prediction that land vegetation profoundly impacted the Earth system is justified, although it is still debated how the individual transitions affected the Earth's O2 and CO2 levels. The geological record preserves multiple lines of indirect evidence for environmental transitions that can help us to reconstruct and quantify global controls on Earth's oxygenation and climate state. © 2020 The Authors