how is the air we breath today different from 3.6 billion years ago?
http://en.wikipedia.org/wiki/Earth's_atmosphere#Evolution_of_the_Earth.27s_atmosphere
http://eesc.columbia.edu/courses/ees/climate/lectures/earth.html
The composition of the air we breathe today is different from what it was 3.6 billion years ago. To understand how the air has changed over such a long time, we can look at scientific research and studies conducted by experts in the field.
One source to find information about the evolution of Earth's atmosphere is the Wikipedia page on Earth's Atmosphere. This page provides an overview of the changes that have occurred over billions of years. You can access this page by typing the following URL into your web browser: http://en.wikipedia.org/wiki/Earth's_atmosphere#Evolution_of_the_Earth.27s_atmosphere
Another source to explore is a lecture on the Earth's atmosphere from Columbia University. This lecture provides detailed information on the history and evolution of the Earth's atmosphere. To access this lecture, you can use the following URL: http://eesc.columbia.edu/courses/ees/climate/lectures/earth.html
By taking the time to read these sources, you will gain a comprehensive understanding of how the air we breathe today differs from what it was 3.6 billion years ago. Always make sure to critically evaluate the information you find and cross-reference it with other reliable sources to ensure accuracy.