Earth, the only life-hosting world we know of, contains signs of that life in its atmosphere. Oxygen/ozone is most convincing, because without being replenished by life, it would disappear quickly. Methane is another one, because it's produces by methanogens. Nitrous oxide is another, because it's produced by microbes and has no known significant source of abiotic production. But finding these chemicals does not necessarily mean there's life there. Earth hosted life long before its atmosphere held oxygen and ozone. And as we've discovered, chemistry on other worlds can be significantly different than here on Earth. Also, exoplanets are at extreme distances, making unambiguous identification of these chemicals challenging. Another approach to finding biosignatures involves using one of the human brain's most extraordinary evolutionary gifts: our pattern finding capability. From this angle, detecting life doesn't depend on any individual chemicals. Instead, it looks for patterns in statistics.…