Text 1
When searching for signs of extraterrestrial life on exoplanets, astrobiologists often focus on detecting atmospheric biosignatures—gases like oxygen and methane that are chemically unstable and require continuous replenishment. Proponents of this search strategy argue that finding these gases in high concentrations in an exoplanet's atmosphere constitutes reliable, primary evidence of biological activity. They assert that typical geological and chemical processes on sterile rocky planets are generally incapable of maintaining such extreme chemical imbalances over long timescales.
Text 2
While atmospheric biosignatures are promising targets, interpreting them is highly complex. Photochemical modeling demonstrates that abiotic processes—such as the photolysis of atmospheric water vapor by stellar ultraviolet radiation followed by the escape of hydrogen into space—can accumulate substantial amounts of oxygen. Without comprehensive data on a host star's ultraviolet output and the exoplanet's rate of water loss, detecting oxygen alone cannot be considered definitive proof of life, since non-biological mechanisms can replicate these signatures.
Based on the passages, how would the author of Text 2 most likely respond to the assertion in Text 1 that high concentrations of biosignature gases are reliable evidence of biological activity?
- ABy claiming that astrobiologists should focus entirely on studying host stars rather than searching for atmospheric biosignatures on exoplanets.
- BBy suggesting that the photolysis of water vapor is a more efficient method of replenishing atmospheric gases than biological replenishment is.
- By noting that certain abiotic processes can generate high levels of these gases, meaning their presence alone does not guarantee a biological source.Answer
- DBy arguing that biological activity is actually less likely to produce detectable levels of oxygen than abiotic geological activity is.