Logical Reasoning

PT144 · S4 · Q19 Researchers working in Western Australia

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

Statements

superlative (oldest) Microdiamonds are the oldest fragment of Earth's early crust that we've identified.

quantitative Microdiamonds are only 50 microns across and were formed 4.2 billion years ago. The Earth formed 4.5 billion years ago (300 million years prior)

Evaluate

There are some Overlapping Ideas (microdiamonds / Earth's crust), but it's not that clear how we would synthesize these statements.

We could say stuff like .

Goal

Overall, there's no Conditional / Causal / Pivot wording to guide us in how they want us to synthesize any of these facts, so let's just head to the answers looking for the most provable claim.

19.

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

  1. Correct

    The Earth's crust took no

    Why this is right

    If the Earth formed, and then 300 million years later, there were already fragments of Earth's early crust, then it seems fair to say that within the first 300 million years of Earth's existence, the crust had started to form. I can see being troubled by this answer in terms of whether "Earth's early crust" was the same as "the Earth's crust". We know that the Earth's early crust had already started forming within 300 million years of Earth, but is that the same as "the Earth's crust"? Or did it have an early crust that eventually disappeared and is now replaced by what we properly call the Earth's crust? It's annoying to tolerate such ambiguity when we're being asked what Must Be True, but ultimately this still seems like the most provable answer.

    Skill tested: Must be True · how this choice captures the argument's function is the move to repeat next time.

    64% picked this

  2. The Earth's crust first formed

    Too Specific: first formed

    Does the fact that we found some microdiamonds in Western Australia, combined with the fact that microdiamonds are fragments of Earth's early crust, prove that Earth's crust first formed in Western Australia? No, where we find an archaeological or geological artifact can just be an accident of history or luck. It may be that the oldest saber-toothed tiger fossil we've found was discovered in Germany, but that doesn't mean that saber-toothed tigers first evolved in Germany.

    2% picked this

  3. The Earth's crust took billions

    Opposite, if anything

    We don't know the "completion date" of the Earth's crust, so ultimately we have no way to judge the truth of this answer. But, if anything, the passage seems to be suggesting that the crust was already in its early stages 300 million years in, so it's very possible that the crust was done forming within 1 billion years.

    14% picked this

  4. Microdiamonds were the first components

    Too Specific: first components

    This is similar to (B). Just because microdiamonds are the oldest fragment we've discovered of the early crust doesn't mean that they are the oldest fragments of the early crust. There might be earlier components of the crust that we simply haven't discovered yet.

    9% picked this

  5. All naturally occurring microdiamonds were

    Too Strong: all

    There's no way we could prove that all microdiamonds ever came from the crust. Whatever geologic conditions inside the Earth that created microdiamonds after the Earth formed might have been in existence at other times / other places. It might be even to this day that the Earth's core is producing microdiamonds that rise up through the mantle or through thermal vents in the bottom of the seafloor.

    10% picked this

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