On Earth, humans have oxygen to breathe. But there’s very little oxygen to breathe in space.
Space is actually a kind of vacuum, which means there isn’t a whole lot of matter, or stuff, out there between the planets and the stars.
![Yimo Liu.](https://wpcdn.web.wsu.edu/wp-cas/uploads/sites/648/2021/10/Yimo-Liu-88-e1635880996463.jpeg)
For Earthlings like you and me, oxygen is an essential part of life. While 21% of Earth’s atmosphere is oxygen, my friend Yimo Liu reminded me it wasn’t always that way.
As a professor of biology at Washington State University, she is very curious about life on our 4.6 billion-year-old planet.
“After we have that first oxygen, other organisms that require oxygen start to evolve,” Liu said.