Finding oxygen in an exoplanet’s atmosphere is a clue that life may be at work. On Earth, photosynthetic organisms absorb carbon dioxide, sunlight, and water and produce sugars and starches for energy ...

Today’s climate change pales in comparison with what happened as Earth gave birth to its oxygen-containing atmosphere billions of years ago. By analyzing clues contained in rocks, scientists at the ...

A rough outline of oxygen (O2) concentrations in Earth's atmosphere through time are illustrated in this figure. Brown blocks show the estimated range for O2 in terms of its present atmospheric level ...