Ancient Moss Brought Oxygen and Life to Earth

The humble moss might be the reason the Earth's air is breathable, scientists say.

Researchers from the University of Exeter in the UK theorized that ancient land plants that colonized the land 470 million years ago might have been responsible for enriching Earth's atmosphere with oxygen.

Today's form of oxygen first appeared in the Earth's atmosphere during the Great Oxidation Event about 2.4 billion years ago, the researchers said. But it was only until about 400 million years that oxygen approached modern levels in the Earth's atmosphere, and this led scientists to seek answers as to how oxygen arrived at its modern concentrations.

According to Tim Lenton, professor at the University of Exeter and lead author of the study, the emergence and evolution of ancient land plants caused the permanent increase in the flow of organic carbon into sedimentary rocks, which are the primary source of oxygen in the atmosphere. This caused oxygen levels to rise and establish a stable cycle on Earth.

Earth's atmosphere now consists of 78 percent nitrogen, 21 percent oxygen, 1 percent argon, and trace amounts of carbon dioxide and other gases. Apart from making the air breathable, oxygen also generates the ozone layer, which protects the Earth from the sun's ultraviolet radiation.

"It's exciting to think that without the evolution of the humble moss, none of us would be here today," Lento said 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."

According to the researchers, Earth's earliest plant biosphere comprised of simple bryophytes, such as moss, which do not have the vein-like systems that transport water and minerals in the plant. After factoring in the properties of modern bryophytes or mosses in computer simulations, the researchers found that modern atmospheric oxygen levels were achieved by 420 to 400 million years ago.

The study was published in the journal Proceedings of the National Academy of Sciences.