Researchers working in Western Australia have discovered the oldest fragments of the Earth's early crust that have ye...

Ravi on May 27, 2019

@claire_crites,

Happy to help. Let's look at (A) and (C).

This is a must be true question, so the answer we pick must be true
based on what we've been told in the stimulus.

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

(C) actually has to be false. The crust took 300 million years or less
to form because we were told that one part of the crust has already
been found 300 million years after the formation of the Earth. If this
is true, then it's impossible that the Earth's crust took billions of
years to form.

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

This has to be true. If the Earth was formed only 300 million years
prior to microdiamonds forming, and microdiamonds are the oldest known
part of the crust, then this means that the Earth's crust must have
been formed within 300 million years. There could be older crust parts
that we are unaware of, and this makes it possible that the Earth's
crust actually took less than 300 million years to form. No matter
what, we know it didn't take any longer than 300 million years to
form.

Does this make sense? Let us know if you have any more questions!