Researchers working in Western Australia have discovered the oldest

Question

Researchers working in Western Australia have discovered the oldest fragments of the Earth's early crust that have yet been identified: microdiamonds. These microscopic crystals measure only 50 microns across and were formed 4.2 billion years ago. This discovery sheds light on how long it took for the Earth's crust to form, since this date is only 300 million years after the formation of the Earth itself.

If the statements above are true, which one of the following must also be true?

If the statements above are true, which one of the following must also be true?

(A) The Earth's crust took no longer than 300 million years to start to form.
(B) The Earth's crust first formed in the area that is now Western Australia.
(C) The Earth's crust took billions of years to form.
(D) Microdiamonds were the first components of the Earth's crust to form.
(E) All naturally occurring microdiamonds were formed at the time the Earth's crust was being formed.

MartyMurray · Accepted Answer

Researchers working in Western Australia have discovered the oldest fragments of the Earth's early crust that have yet been identified: microdiamonds. These microscopic crystals measure only 50 microns across and were formed 4.2 billion years ago. This discovery sheds light on how long it took for the Earth's crust to form, since this date is only 300 million years after the formation of the Earth itself.

If the statements above are true, which one of the following must also be true?

If the statements above are true, which one of the following must also be true?

This is an Inference question, and the correct answer will be the choice that must be true given what the passage says.

(A) The Earth's crust took no longer than 300 million years to start to form.

This choice is interesting.

After all, the passage indicates that the microdiamonds are fragments of Earth's crust and were formed 4.2 billion years ago, which is only 300 million years after the formation of Earth itself. That information indicates that the crust also must have formed only 300 million years after the formation of Earth itself.

After all, if part of the Earth's crust was formed 300 million years after the formation of Earth, then the crust started to form then.

Also, the passage says the following:

This discovery sheds light on how long it took for the Earth's crust to form, since this date is only 300 million years after the formation of the Earth itself.

That statement indicates that we can safely presume that, by "how long it took for the Earth's crust to form," the passage and choice (A) mean "how long after the formation of Earth it took for Earth's crust to form," rather than how long after the universe formed or how long in some other way.

So, given what the passage says, we can decide that the correct answer is "The Earth's crust took no longer than 300 million years to start to form."

Keep.

(B) The Earth's crust first formed in the area that is now Western Australia.

The passage does not indicate the location at which the crust "first formed."

It indicates only that "the oldest fragments of the Earth's early crust that have yet been identified" were found in Western Australia.

The fact that the oldest fragments found were there does not mean that it "must be true" that the crust first formed there. After all, there could be older fragments elsewhere, or the fragments found there could have formed elsewhere and then somehow been transported to Western Australia.

Eliminate.

(C) The Earth's crust took billions of years to form.

To an extent, this choice contradicts what the passage says.

After all, if microdiamonds, parts of Earth's crust, were formed only 300 million years after Earth itself, then it appears that Earth's crust formed to at least some extent within 300 million years.

Furthermore, even if, given what the passage says, it may have taken over 300 million years for Earth's crust to form completely, there still is nothing in the passage that indicates that Earth's crust took "billions of years" to form.

Eliminate.

(D) Microdiamonds were the first components of the Earth's crust to form.

The passage does not indicate that microdiamonds were "the first components of the Earth's crust to form."

It indicates only that they are the oldest fragments of Earth's crust "that have yet been identified."

The fact that nothing older has been identified does not mean that it "must be true" that they were the first components of the Earth's crust to form.

There could be other components that have not been identified that formed before microdiamonds.

Eliminate.

(E) All naturally occurring microdiamonds were formed at the time the Earth's crust was being formed.

This choice is a little hard to eliminate because the passage says the following:

Researchers working in Western Australia have discovered the oldest fragments of the Earth's early crust that have yet been identified: microdiamonds.

That part of the passage seems to basically define microdiamonds as fragments of Earth's early crust.

So, to eliminate this choice, we have to make a judgment call and decide that the fact that microdiamonds can be fragments of Earth's early crust does not mean that all microdiamonds are fragments of Earth's early crust.

Honestly, this question could be a little better constructed since the above sentence from the passage does seem to indicate that microdiamonds are by definition parts of Earth's early crust. At the same time, since it's not clear that that's what the above sentence is meant to convey and since choice (A) is clearly supported by the passage, we can eliminate this choice and choose (A).

Eliminate.

Correct answer:   A

capnmoron · Answer

I don't see a reference time being mentioned, hence I believe C should also be correct, since it took Earth billions of years to form, Earth's crust will succeed that formation.

guddo · Answer

Researchers working in Western Australia have discovered the oldest fragments of the Earth's early crust that have yet been identified: microdiamonds. These microscopic crystals measure only 50 microns across and were formed 4.2 billion years ago. This discovery sheds light on how long it took for the Earth's crust to form, since this date is only 300 million years after the formation of the Earth itself. 
 
If the statements above are true, which one of the following must also be true?

The passage says the Earth formed 4.5 billion years ago, and the microdiamonds, which are fragments of the early crust, formed 4.2 billion years ago.  So the crust must have started forming within 300 million years of Earth’s formation .

(A) The Earth's crust took no longer than 300 million years to start to form.

This is correct. If fragments of early crust existed 300 million years after Earth formed, then the crust must have started forming by that time.

(B) The Earth's crust first formed in the area that is now Western Australia.

This is unsupported. The oldest identified fragments were found there, but that does not prove the crust first formed there.

(C) The Earth's crust took billions of years to form.

This is not supported. The passage suggests crust formation began relatively early.

(D) Microdiamonds were the first components of the Earth's crust to form.

This is too strong. They are the oldest fragments identified, not necessarily the first components that formed.

(E) All naturally occurring microdiamonds were formed at the time the Earth's crust was being formed.

This is unsupported. The passage discusses these particular  microdiamonds , not all microdiamonds.

Answer: (A)

egmat · Answer

Hi capnmoron,

I see exactly where this is coming from, so let's untangle it.

Two things are happening in your reasoning, and both trace back to the same slip: an assumption that the stimulus never actually gives you.

First, the reference time  is  stated.  The passage says the microdiamonds "were formed  4.2 billion years ago ... only  300 million years  after the formation of the Earth itself." So the clock is anchored to the formation of the Earth - that's the reference point choice A uses, too.

Second - and this is the key - nothing in the passage says the Earth took "billions of years to form."  You're importing that idea from outside the argument. For a must-be-true question, you can only use what the stimulus states, and it never gives a duration for the Earth's formation.

Now look at what the passage  does  force to be true. The microdiamonds are literally "fragments of the Earth's early crust," and they already existed  4.2 billion years ago . That means a piece of crust  existed  just  300 million years  after the Earth formed. If crust already existed by then, it simply cannot have taken  billions  of years to start forming - so choice  C actually contradicts the passage  rather than following from it.

Think of it plainly: if a fragment of the crust was already sitting there at the  300 -million-year mark, the crust's start can't be billions of years out.

Quick way to test the trap:  cross out anything you're "adding" and reread only the printed sentences.
- Does the passage state how long the Earth took to form?  No. 
- Does it state a piece of crust existed  300 million years  after the Earth?  Yes.

Once you keep only what's on the page, C falls away and A is the safe inference.

Answer: A

Researchers working in Western Australia have discovered the oldest

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