Researchers working in Western Australia

Answer choices

1. A

   Correct64% picked this

   The Earth's crust took no longer than 300 million years to

   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%
2. B

   Too Specific: first formed3% picked this

   The Earth's crust first formed in the area that is now

   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.

   3%
3. C

   Opposite, if anything14% picked this

   The Earth's crust took billions of years

   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%
4. D

   Too Specific: first components9% picked this

   Microdiamonds were the first components of the Earth's crust

   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%
5. E

   Too Strong: all10% picked this

   All naturally occurring microdiamonds were formed at the time the Earth's crust

   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%