Earth's Oxygen Gap Warns Planet-Hunting Telescopes May Miss Life

Life on Earth existed for about 3.5 billion years before atmospheric oxygen and ozone became detectable from afar. That means NASA’s future Habitable Worlds Observatory could directly image an Earth-like planet and still find no decisive life signs if its atmosphere is oxygen-poor, underscoring that biosignatures are context‑dependent and that searches must rely on multiple gases and signals rather than oxygen alone.