the conclusion states "therefore, ancestors of modern humans lived in western asia between 2 million and 1.5 million years ago"
which is an assumption required by the argument?

C) the lava that lay under the lake -bottom sediments did not contain an human fossil remains.
using ANT= the lava that lay under the lake bottom sediments did contain human fossil remains would imply that ancestors of modern humans lived in asia prior to 2 million years ago, causing the authors conclusion to be invalid (the timeframe would be earlier then 2 million years ago.

Why is C wrong?

E uses the same methodology. per the answer key "if bones were not already in the sediment when the lake disappeared, that means they got into the sediments later; that is less than 1.5 million years ago.... then timeframe is no longer valid as presented in the conclusion"

Here's our timeline, according to the stimulus:

-2million yrs: lava dams up river and creates lake
-1.5 million yrs: lake ceases to exist

We find bones in the lake sediments on TOP of the lava - causing us to conclude that there were humans living there while the lake was in existence.

In C, we talk about not finding human remains in the lava -- except that this doesn't pertain to our conclusion. Our conclusion is that humans were there DURING the existence of the lake - whether they were there before that (i.e. when the lava came through) or not is irrelevant. There MIGHT have been humans there before the lake was in existence - or there might not have been - it doesn't have any effect on whether there were humans there DURING the existence of the lake.

Make sense?

Veritas Help

I am still a little bit confused.
the conclusion is "Therefore, ancestors of modern humans lived in Western Asia between 2 million and one and a half million years ago." (nothing in the conclusion specifically mentions that humans lived during the time of the lake's existence)

This conclusion is in the form of a max and min range of possible dates. If anything falls outside of these dates, the conclusion is invalid, in my opinion. (ANT on Answer C) So it is of importance if the lava that lay under the lake bottom contained human fossil remains, as it shows that humans lived prior to 2 million years ago, which is a violation of the range expressed in the conclusion.

Answer E follows the same logic, it presents the statement that bones were present after 1.5 million years, again a violation of the date range in the conclusion.

How is E better than C?

Choice C is not an assumption required by the argument. Focus on the conclusion and the assumptions required by it.

The conclusion is that humans lived in Western Asia 1.5 - 2.0 million years ago.

Whether or not they lived there before or after that is not relevant.

-Veritas Help