What is the composition of Mars' atmosphere?

The composition of Mars' atmosphere is 95.32 percent carbon dioxide, 2.7 percent nitrogen, 1.6 percent oxygen and 0.08 percent carbon monoxide. The remaining 0.3 percent is made up of various trace elements.

One of the trace elements detected in the Martian atmosphere is methane. The discovery of methane on Mars caused some excitement in the scientific community because the presence of methane is regarded as a sign that life might have, at one time, existed on Mars. However, while methane is sometimes a byproduct of life processes, it can also be a product of volcanic activity and geothermic processes, so there is still no proof that there was ever life on Mars.