Our Earth is about 4.5 billion years old and, through careful work, scientists have pieced together a timeline of its past. But much of its earliest history remains a mystery. Scant geological ...

The appearance of oxygen in Earth's atmosphere was a turning point in the history of our planet, forever transforming the environment and setting the stage for complex life. This event, known as the ...

First came the surprising discovery that Earth’s atmosphere is leaking. But for roughly 60 years, the reason remained a mystery. Since the late 1960s, satellites over the poles detected an extremely ...