The earliest land plants enabled the rise of animals.
Plants slowly emerged from the water and colonized land around 470 million years ago. Soon after, simple bryophytes, such as mosses, were forming lush green carpets throughout the world.
This was around 2 billion years after the Great Oxygenation Event — brought on by photosynthesis of cyanobacteria — introduced low levels of free oxygen into the atmosphere.
But researchers now believe that these early plants were responsible for enriching the atmosphere with the levels of oxygen required to sustain life today.
Using computer models, the researchers predict that by repeatedly taking up carbon dioxide from Earth’s atmosphere and sending oxygen back out, ancient mosses brought atmospheric oxygen up to present-day levels by around 400 million years ago
“Their emergence and evolution permanently increased the flux of organic carbon into sedimentary rocks, the primary source for atmospheric oxygen, thus driving up oxygen levels in a second oxygenation event and establishing a new, stable oxygen cycle,” the authors write in Proceedings of the National Academy of Sciences.
The oxygen boost enabled larger life forms, including humans, to evolve.
“It’s exciting to think that without the evolution of the humble moss, none of us would be here today,” says lead author Tim Lenton, from the University of Exeter, in a press release.
“Our research suggests that the earliest land plants were surprisingly productive and caused a major rise in the oxygen content of the Earth’s atmosphere.”
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