ConceptChecks
ConceptCheck 27-1: Carbon atoms can combine with other elements to form an impressively wide array of different molecules, and this complexity is needed for even the smallest living organisms. Furthermore, carbon is produced in stars and is widely available.
ConceptCheck 27-2: Organic molecules are commonly found in meteorites and comets, which frequently crashed onto planet surfaces during the early formation of the solar system. Also, interplanetary dust grains containing organic compounds steadily fall to a planet’s surface.
ConceptCheck 27-3: They created amino acids and other compounds that living organisms need—they did not create living entities.
ConceptCheck 27-4: The salts dissolve in water when the water is in contact with rock. Rather than a small pocket of water within ice, the salts suggest a much larger ocean is in contact with a rocky mantle.
ConceptCheck 27-5: Living organisms that depend on photosynthesis concentrate 12C compared to their surroundings. This increased abundance can remain in the environment long after the organisms are dead.
ConceptCheck 27-6: Geological processes (involving no biology) can also produce this type of magnetite, so there is no compelling reason to assume that the magnetite was produced by Martian microbes. (Note: The claims that this magnetite was of biological origin came before it was figured out that this magnetite can be produced through geology.)
ConceptCheck 27-7: The Martian meteorites have trace amounts of gas trapped within them that are nearly identical to the unique Martian atmosphere.
ConceptCheck 27-8: At the speed of light, radio waves travel at more than 100,000 km every second, whereas our fastest spacecraft can only travel at tens of thousands of kilometers every hour. Therefore, the vast distances between the stars make it seemingly impossible for spacecraft to carry out exploration of the stars.
ConceptCheck 27-9: L is particularly difficult to estimate because at about the same time the technology to communicate beyond one’s own planet is developed, the technology of weapons of mass destruction can develop, which could end the civilization just as it starts (alternatively, it can learn to live without war and exist for a very long time).
ConceptCheck 27-10: At other frequencies, there is more background noise, and more energy would need to be used to reliably transmit the same message across the Galaxy. Any advanced civilization could figure this out and would see the benefits of sending messages in this narrow range.
ConceptCheck 27-11: The Kepler telescope was looking for an ever-so-slight dimming of a star as an orbiting planet passes in front of the star, partially blocking the star from our view. This is called a transit.
ConceptCheck 27-12: If the orbital plane of a planet around its star is tilted up or down from our perspective, then the planet will not block out any of the star’s light during its orbit. Since Kepler looked for the dimming of stars as they were blocked by planets, Kepler would not have detected a planet with this kind of orbit.
ConceptCheck 27-13: Ozone comes from oxygen gas, O2, which is produced by living organisms on Earth. Scientists do not know of any plausible nonbiological way to create a dense oxygen atmosphere.
ConceptCheck 27-14: In the infrared where a planet’s spectrum can be more easily measured, an absorption line from oxygen gas is not present, but absorption from ozone (O3) is.