Scientists have been pursuing the answer to a question for a long time, that is: what gives the earth enough oxygen to enable it to breed animals and humans. Oxygen appeared in the earth's atmosphere 2.4 billion years ago. About 470 million years ago, bryophytes spread rapidly on the earth. It was not until 400 million years ago that the oxygen content in the earth's atmosphere reached today's level. 
The spread of bryophytes increases the organic carbon content in sedimentary rocks, which leads to an increase in the oxygen content in the air.
 some scientists believe that the large increase in oxygen on the earth originated from bryophytes.