medium · Act english
An astrobiologist is describing the search for 'biosignatures' in exoplanet atmospheres. [1] Using spectroscopy, scientists analyze the light passing through a distant planet's atmosphere to identify specific gases. [2] The presence of oxygen and methane in high concentrations would be highly suggestive of life, as these gases tend to react and disappear unless they are constantly replenished. [3] However, scientists must be cautious, as geological processes like volcanism can also produce these gases in some environments.
Which choice best introduces the paragraph?
- Volcanoes can be found on many planets and moons, and they release a variety of gases into the air.
- The universe is vast, and many astronomers believe it is statistically certain that we are not alone.
- Oxygen is a vital gas that allows most life on Earth to survive through the process of respiration.
- Identifying life on other planets requires a careful analysis of atmospheric gases and their origins.
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