Life On Earth
By The Science Room

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Two scientists were asked the question, How did life originate on the planet Earth? Their views are presented below.

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.

Scientist 2: 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: