Life, but not as we know it

Here is a problem that has been quietly gnawing at astronomers for decades. The standard approach to detecting life on other worlds involves scanning exoplanet atmospheres for oxygen, methane, and ozone, whose presence is difficult to explain without biology. It's a clever idea, but it carries a hidden flaw. That entire shopping list was written by studying Earth. It is, inevitably, a search for life like us.