Over 500 exoplanets have been discovered so far, some being rocky, terrestrial planets. Advancing instrumentation
permits spectroscopic examination of their atmospheres, and remote detection of potential of biogenic gases. Of
particular interest are oxygen and methane, although other gases are considered. Short residence time of these gases
implies continued renewal. Abiotic sources are considered at levels that could be misinterpreted as a pseudobiosignature.
Photodissociation of water molecules, for example, could produce an oxygen pseudo-biosignature,
although generally at low levels. However, large-scale water loss events, as are thought to have occurred on Venus and
Mars, could produce a substantial pseudo-biosignature.
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