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Listen to part of a lecture in an astronomy class. Professor: Now, when we think about the possibility of life beyond Earth, we often focus on finding liquid water. But today I want to discuss a different approach: looking for biosignatures in planetary atmospheres. A biosignature is any substance or pattern that provides scientific evidence of past or present life. For example, on Earth, the simultaneous presence of oxygen and methane in our atmosphere is a strong biosignature because these gases react with each other quickly. If they exist together, something must be constantly producing them—like living organisms. However, detecting such gases on exoplanets is tricky. Telescopes like the James Webb Space Telescope can analyze the light passing through a planet's atmosphere during a transit. By splitting that light into a spectrum, we can identify which gases are present. But there's a catch: geological processes, like volcanic activity, can also produce methane. So we need to look for combinations of gases that are unlikely to exist together without life. One promising pair is oxygen and methane, but we also need to consider the planet's overall environment, such as its temperature and star type, to avoid false positives. This is why the search for life is not just about finding one molecule—it's about understanding the whole system.