Earth's early atmosphere may have been coughed up in volcanoes. You're on the right track here, Terrell. Plants have transformed the air we breathe, by adding oxygen to the atmosphere. But plants and trees didn't create Earth's air. Scientists say Earth got its first atmosphere billions of years ago, when our planet was born.
Scientists think that giant rocks in space smashed together when Earth was forming.
Many scientists believe that, sometime around four billion years ago, simple life arose. But there was still no oxygen. Terrell, thanks for your question. And thanks to the National Science Foundation for making our show possible.