biosignature

A chemical or physical sign that may show that living things are present or were present in the past.

In the search for life beyond Earth, a biosignature may be a gas or combination of gases in a planet’s atmosphere. It is evidence to investigate, not proof of life, because nonliving processes can sometimes produce similar signs. The word also applies to possible signs of life in rocks, soil, or other environments.

• We may have found a biosignature in the planet’s atmosphere, but the signal needs more study.
• The team is checking whether the gas is a biosignature or the result of a nonliving process.
• Before calling it a biosignature, scientists need to rule out processes that could produce the same gas without life.