PT156.S1.P4.Q27 > Analytics

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Discovered in 1993, the site known as Ukhaa Tolgod, in the Gobi desert of Mongolia, is one of the world's best sources of fossils from the Late Cretaceous period, which ended about 65 million years ago. ███ █████████ ███████ ███ ██████ ███████ ████ ████ █████ █████████ ████████ ██████████ ████ ████ █ ███████████ ███████ ███ ███████████████ ████ ██████████ ███

Phenomenon · Well preserved fossils

How did they form?

Hypothesis · Sandstorm buried the animals

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Hypothesis wrong · New evidence calls sandstorm hypothesis into question

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Details of Phenomenon · Three different types of sandstone at the site

1st Type · Well-defined structure

Consistent with sandstorm hypothesis...

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2nd Type · Tilt and layering

Also consistent with sandstorm hypothesis...

3rd Type · No layering; contains large pebbles

Inconsistent with sandstorm hypothesis because the pebbles are too large to have been windblown. This is the type that contains all of the vertebrate skeletal fossils.

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Alternate Hypothesis · Sand avalanche caused fossils

Avalanche trapped animals in its path, resulting in the pristine quality of the remains.

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Phenomenon · Avalanche / sandslides

What caused them?

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Hypothesis · Unclear; clay played a role

Unclear but likely clay and rain played a role.

Evidence · Modern sand dunes

Implications of hypothesis · Sandslide hypothesis suggests area was not sterile desert

Passage Style

Critique or debate

Phenomenon-hypothesis (RC)

27.

Which one of the following, ██ █████ ████████ ███ █████████ ███████ ███ ████████ ████ ███ ███████ █████ ██████████ █████████ ████ █████ ██ █████ ██████ ████ ██████ ██ ███████████

Question Type

WSE (RC)

We’re trying to weaken the author’s argument supporting the sandslide theory. One way might be to show that observations about modern sand dunes aren’t as relevant as the author thinks to sand dunes in the past. Another way to weaken could be to show that sandslides aren’t the only explanation for how fossils can become trapped in the third type of sandstone. Remember, the author jumped to sandslides merely because the third type of sandstone “exhibits a structure similar to that caused by” sandslides. But the sandstone structure might also be similar to structures formed by things besides sandslides.

Scientists have never ████████ ████████ ███████ █████ ██████ ██ █ █████████ ██ ███ ████ ███████

Whether scientists have directly observed animals being killed by a sandslide in the Gobi doesn’t bear on whether a sandslide could have killed animals in the Gobi desert 65 million years ago. As long as sandslides can kill animals, the authors’ theory can be supported by other evidence. No one needs to directly witness a death due to sandslide in order for such a death to be a reasonably possible occurrence.

The area of ███ ████ ██████ ██ █████ █████ ██████ ██ ███████ ██ █████████ ███ █ ██████ ████ ██████

The current state of the site doesn’t impact whether the site could have been a stable dune 65 million years ago.

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We already know that no fossils were found in the second type of standstone at Ukhaa Tolgod. So whether fossils have been found in that kind of stone at different sites has no impact. The argument is about Ukhaa Tolgod.

26%

Geologists believe that ██ ██████████ ████ ████████ ██ ███ ████ ██████ ███ ██ █████ █ ███████ ██████

The argument is about what happened 65 million years ago. The fact sandslides haven’t occurred in 5 million years doesn’t relate to whether they could have occurred 65 million years ago.

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This weakens by providing an alternate explanation for how the fossils can be found in the third type of sandstone. Remember, the author jumped to sandslides as the explanation merely because the third type of sandstone “exhibits a structure similar to that caused by” sandslides. But if other natural processes can produce the third type of sandstone, then that raises the possibility another natural process besides a sandslide occurred to make the sandstone have the structure it does. We don’t need to jump to the sandslide hypothesis.

57%

PrepTest 156 - Section 1 - Passage 4 - Question 27

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