PrepTest 144, Section 4, Question 19
Researchers working in Western Australia have discovered the(58 more words not shown)
If the statements above are(10 more words not shown)
- AThe Earth's crust(11 more words not shown)
- BThe Earth's crust(10 more words not shown)
- CThe Earth's crust(6 more words not shown)
- DMicrodiamonds were the(8 more words not shown)
- EAll naturally occurring(12 more words not shown)
Reading the argument
Finding the oldest known piece of crust tells us the crust existed by that time. It doesn't tell us that nothing formed earlier. The dates give us a useful limit. Earth formed 300 million years before these 4.2-billion-year-old crystals formed. Since the crystals were part of its early crust, the crust must have started forming within those first 300 million years. It could have started sooner.
Keep “started” separate from “finished.” Finding a piece of crust doesn't tell us when the whole process was complete. And finding it in Western Australia doesn't establish that crust first formed there; earlier material elsewhere could be undiscovered or gone.
What we’re looking for
For the must-be-true question, I want a conclusion that stays within that timing limit. We know the crust was underway by the time these crystals formed.
Working the answers
- ACorrect
The crust took no longer than 300 million years to start forming. By that point, these identified pieces of it existed. The answer allows an earlier start and makes no claim about when formation finished, so it stays within what the discovery establishes.
- B
The location of the oldest fragments identified so far isn't necessarily the location where crust first formed. Other early fragments could have formed elsewhere and been destroyed or simply not found. Western Australia is the discovery site, not an established point of origin.
- C
Something forming billions of years ago is different from its taking billions of years to form. We aren't given the duration of the whole process. It might have continued much longer, but these statements don't establish that.
- D
These are the oldest fragments yet identified. That doesn't make them the first components ever formed. Another material could have formed earlier without researchers having found an older surviving example of it.
- E
The passage dates these particular microdiamonds, not all naturally occurring microdiamonds. Others might have formed later or in another setting. Knowing the history of the discovered crystals doesn't establish the history of every crystal of that kind.
More Must Be True questions
Learn the LSAT our way
Our platform drills Must Be True questions at your level and adjusts as you improve.