Scientist 1:

The idea that earth could have given rise to life independently is mistaken. Life on this planet must have come from elsewhere for several reasons. First of all, complex life appears very suddenly in the geological record. Secondly, all life on earth has a very similar biochemistry. If life originated on earth, one would expect regional variations in biochemistry, similar to the variations in species spread over large areas. Finally, the time when life first appeared in the geological record was also a time when large numbers of meteorites struck the earth. The meteorites must have caused life to appear on the earth. The simplest hypothesis is that the meteorites brought life with them.

Life need not have been imported from outer space. The chemicals required for life existed on the surface of the earth at the time life first appeared. The fact that all life has a similar biochemistry can be explained by considering that any group of chemicals that won the race to life would probably have used the almost-living as food. Since we can offer explanations for what happened without relying on a meteorite of unknown composition that might have fallen to earth, we should stick to hypotheses that have fewer unknowns.

Use the two scientist's views to select the best answer for each of these questions:

1. Which of the following is an assumption of Scientist 1?

1. Complex life forms can develop quickly.
2. Meteorites burn up as soon as they hit the earth's atmosphere.
3. There is a cause-and-effect relationship between meteors falling and the origin of life on earth.
4. The changes on the earth's surface due to the presence of life attracted meteor showers.

2. Which of the following, if true, strengthens Scientist 2's argument the most?

1. Only 5% more meteors than normal fell on the earth during the time life began.
2. Only 5% of the meteorites studied contained organic molecules.
3. A simulation of early earth chemistry showed the spontaneous formation of comples biomolecules.
4. Meteorites containing amoebas have been found.

3. Which of the following, if true, strengthens Scientist 1's argument the most.

1. Only 5% more meteors than normal fell on the earth during the time life began.
2. Only 5% of the meteorites studied contained organic molecules.
3. A simulation of early earth chemistry showed the spontaneous formation of comples biomolecules.
4. Meteorites containing amoebas have been found.

4. Which explanation of the similar biochemistry of all life on earth would Scientist 1 most likely agree with?

1. A single chemical pathway to life exists.
2. Life arose from a single source.
3. Life is not varied.
4. Meteors are simple.

5. Which explanation of the similar biochemistry of all life on earth would Scientist 2 most likely agree with?

1. A single chemical pathway to life exists.
2. Life arose from a single source.
3. Life is not varied.
4. Meteors are simple.

6. Which scientist would be likely to disagree with the idea that life on different planets could have different biochemistries?

1. Scientist 1
2. Scientist 2
3. Both
4. Neither

7. Which of the following questions would be the most difficult for Scientist 1 to defend his view against?

1. Why was there more meteorite activity earlier in earth's history?
2. Why haven't other meteors brought other life based on a different biochemistry?
3. Why did complex life emerge suddenly?
4. Why should meteor activity have any connection to the origin of life?

8. Could Scientist 2 believe that life exists on other planets without affecting his hypothesis?

1. Yes, as long as he believes that life elsewhere has a different biochemistry.
2. Yes, because wherever the chemicals required for life exist, life can begin.
3. No, because then he has to admit that meteorites brought life from these plantes.
4. No, because then he has to admit that meteorites that came from pieces of similar planets brought life to earth.