According to an international study, the first land plants, including bryophytes/mosses, may explain how the Earth was oxygenated.
Oxygen initially appeared in the Earth’s atmosphere 2.4 billion years ago during the “Great Oxidation Event.” It wasn’t until land plants colonized the Earth around 470 million years ago when oxygen levels reached current levels. This second oxygenation event allowed for the emergence of animal and human life.
The study states,
We use a trait-based ecophysiological model to predict that cryptogamic vegetation cover could have achieved ∼30% of today’s global terrestrial net primary productivity by ∼445 Ma. Data from modern bryophytes suggests this plentiful early plant material had a much higher molar C:P ratio (∼2,000) than marine biomass (∼100), such that a given weathering flux of phosphorus could support more organic carbon burial. Furthermore, recent experiments suggest that early plants selectively increased the flux of phosphorus (relative to alkalinity) weathered from rocks. Combining these effects in a model of long-term biogeochemical cycling, we reproduce a sustained +2‰ increase in the carbonate carbon isotope (δ13C) record by ∼445 Ma, and predict a corresponding rise in O2 to present levels by 420–400 Ma, consistent with geochemical data. This oxygen rise represents a permanent shift in regulatory regime to one where fire-mediated negative feedbacks stabilize high O2 levels.
The emergence of bryophytes increased the amount of carbon into sedimentary rock, which are the primary source of atmospheric oxygen. This drove up the oxygen levels into a stable oxygen cycle.
Bryophytes are non-vascular-like plants. They do not have veins to circulate water and minerals around the plant. Moss falls into this category.
The researchers used computer simulations to conduct the study. They estimated that the moss may have generated the stable, life-sustaining oxygen levels.
Professor of Geology Tim Linton, Chair in Climate Change/Earth Systems Science at the University of Exeter in the U.K. says,
It’s exciting to think that without the evolution of the humble moss, none of us would be here today. Our research suggests that the earliest land plants were surprisingly productive and caused a major rise in the oxygen content at Earth’s atmosphere.