PrepTest 136, Section 4, Question 10
In an experiment designed to show how life(75 more words not shown)
Assuming that the scientists' current(34 more words not shown)
- AMeteorite impacts at(15 more words not shown)
- BA single amino(13 more words not shown)
- CEarth's atmosphere has(6 more words not shown)
- DLightning was less(12 more words not shown)
- EAsteroids contain amino(14 more words not shown)
Reading the argument
Making one building block of life is not the same as explaining all of life. So when lightning produces amino acids, I want to know what that result actually establishes.
The experiment also has a condition that matters. Amino acids form more readily and hold together better in a reducing atmosphere: plenty of hydrogen and little oxygen. Outside that setting, they are harder to form and tend to break apart. Yet the early Earth is described as rich in oxygen. That makes the experimental conditions look like a poor fit for the planet where life began.
Could there have been pockets with different conditions? The atmosphere overall could have contained plenty of oxygen while a particular place temporarily had the reducing conditions the experiment needs. That is where I'd look for a way to reconcile the two facts.
What we’re looking for
The question specifically asks how lightning could have produced the first amino acids. We can accept the scientists' belief about the overall atmosphere while looking for a local exception that would let the process work.
Working the answers
- ACorrect
A meteorite impact temporarily creates a reducing atmosphere around the impact site. There is our pocket: local conditions suitable for lightning to produce amino acids, even though the atmosphere more generally is oxygen-rich. The answer helps explain formation under favorable conditions; we do not need to add a story about every later stage in the development of life.
- B
This lowers the number of amino acids needed to start the process of life. But it does not explain how lightning produced that first amino acid in an atmosphere where formation is difficult and the molecules tend to break apart. Formation is not stated to be impossible; B simply does less than A to explain how the environmental difficulty was overcome.
- C
Changes since life began do not tell us how amino acids formed at the time life began. The question instructs us to accept the scientists' current belief about that earlier atmosphere. A later change does not provide the needed favorable conditions then.
- D
Less frequent lightning does not explain how a lightning strike could produce amino acids under the stated atmospheric conditions. The puzzle is about the conditions under which the strike works, not why there were many strikes.
- E
This could explain how amino acids arrived on Earth from elsewhere. But arriving already formed on an asteroid is different from being produced by lightning on Earth. A meteorite matters in A because it changes the local atmosphere; the asteroid in E merely delivers the molecules. Only the first route answers the question asked.
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