Q 22
Photosynthesis, once it was planet-wide, changed the atmosphere of the Earth by introducing a significant amount of
A) oxygen
B) carbon dioxide
C) methane
D) ammonia
E) vibranium
Q 23
Which of the following is a biomarker that could be used from an observatory around a nearby star, with the right equipment, to identify the Earth as a planet with life:
A) the presence of a large moon around the Earth
B) free oxygen in the Earth's atmosphere
C) the abundance of micro-organisms in the deserts of the Earth
D) the fact that most of our atmosphere is made of nitrogen
E) ice in the Earth's polar caps
Section 30.4: The Search for Extraterrestrial Intelligence
Q 24
Which of the following is a good summary of what most astronomers think about UFO reports in the popular media?
A) so far there is no scientific evidence that UFO's have anything to do with life outside the Earth
B) it is now clearly established that alien spacecraft have crashed on Earth; we have the bodies of the aliens who flew them here
C) while no UFO's have landed, we have overheard communications between them with our radio surveys and thus have evidence that there are intelligent creatures aboard them
D) UFO's are now known to come from the planet Mars, the only other planet that we know has life on it
E) UFO's have kidnapped a number of Earth inhabitants, including at least one well-known astronomer; her reports convinced other scientists that UFO's are indeed alien spaceships
