Question

passage i

in a particular playa (relatively flat, dry desert basin) evidence shows that some large rocks have moved along the surface, leaving shallow trails in the clay sediment, some up to several hundred meters long. three scientists provided explanations for how these rocks moved.

scientist 1

in the spring, snowmelt from surrounding mountains runs downhill and collects in the playa. at night, cold temperatures cause this water to freeze around the rocks. when temperatures rise again, the ice begins to melt, leaving a layer of mud on the surface and ice
afts\ around the rocks. the buoyancy of the ice rafts floats the rocks on top of the mud such that even light winds can then push the rocks along the surface. evidence of this lifting is seen in that the trails left by rocks are both shallow and only about 2/3 as wide as the rocks themselves. due to the combination of ice, mud, and light winds, the rocks are able to move several hundred meters in a few days.

scientist 2

snowmelt from surrounding mountains does collect in the playa during the spring. however, the temperature in the playa does not get cold enough for ice to form. when the playas surface gets wet, the top layer of clay transforms into a slick, muddy film. in addition, dormant algae present in the dry clay begin to grow rapidly when the clay becomes wet. the presence of mud and algae reduces friction between the rocks and the clay. even so, relatively strong winds are required to push the rocks along the wet surface, forming trails. due to the combination of mud, algae, and strong winds, the rocks are able to move several hundred meters in a few hours.

scientist 3

water does collect in the playa, producing mud and ice. however, neither mud nor ice is responsible for the rocks movements. the playa is located along a fault line between tectonic plates. minor vertical shifts in the plates cause the rocks to move downhill, leaving trails. due to the combination of tectonic plate movement and strong winds, the rocks are able to move only a few meters over several years.

1. according to scientist 2, friction between the rocks and the clay is reduced by which of the following?

a. ice only
b. algae only
c. ice and mud only
d. mud and algae only

1. suppose a researcher observed that wind speeds greater than 80 miles per hour are needed to move the rocks in the playa. this observation is consistent with which of the scientists explanations?

f. scientists 1 and 2 only
g. scientists 1 and 3 only
h. scientists 2 and 3 only
j. scientists 1, 2, and 3

1. suppose that no seismic activity was recorded in the playa where the trails left by the rocks are found. this finding would weaken which of the scientists explanations?

a. scientist 1 only
b. scientist 3 only
c. scientist 1 and scientist 2 only
d. scientist 2 and scientist 3 only

1. suppose it were discovered that a particular rock formed a 200 m long trail in 72 hr. would this discovery support scientist 1s explanation?

f. yes; scientist 1 indicated the rocks can move several hundred meters in a few hours.
g. yes; scientist 1 indicated the rocks can move several hundred meters in a few days.
h. no; scientist 1 indicated the rocks can move several hundred meters in a few hours.
j. no; scientist 1 indicated the rocks can move several hundred meters in a few days.

Explanation:

Question 1

To solve this, we analyze Scientist 2's explanation. Scientist 2 says "the presence of mud and algae reduces friction between the rocks and the clay". So we check the options: A is ice only (Scientist 2 doesn't mention ice), B is algae only (but also mud), C is ice and mud (no ice), D is mud and algae (matches Scientist 2's statement).

• Scientist 1: Needs light winds (so wind <80 mph can move rocks, so if 80+ is needed, inconsistent? Wait, no—Scientist 1 says light winds (so less than 80) can move. If 80+ is needed, Scientist 1's explanation would not be consistent? Wait, no, re - read. Scientist 1: "even light winds can then push the rocks along the surface". So if 80+ is needed, Scientist 1's explanation is inconsistent. Scientist 2: "relatively strong winds are required to push the rocks along the wet surface". So 80+ could be strong, so consistent. Scientist 3: "strong winds" and tectonic movement. So 80+ could be strong, consistent. Wait, no—wait the question is "this observation (wind speeds >80 mph needed) is consistent with which scientists' explanations?". Scientist 1: light winds (so <80) can move. So if >80 is needed, Scientist 1's explanation is not consistent. Scientist 2: needs relatively strong winds—so 80+ could be strong, consistent. Scientist 3: needs strong winds—80+ could be strong, consistent. So Scientists 2 and 3 only (option H). Wait, let's re - check:

Scientist 1: "even light winds can then push the rocks along the surface"—so if you need >80 (strong), Scientist 1's explanation (light winds enough) is not consistent. Scientist 2: "relatively strong winds are required"—so 80+ is strong, consistent. Scientist 3: "strong winds"—80+ is strong, consistent. So Scientists 2 and 3 only (H).

• Scientist 1: Says ice forms (since "at night, cold temperatures cause this water to freeze around the rocks"). If no ice forms (no seismic, but also no ice), Scientist 1's explanation is weakened (since ice is part of their mechanism). Scientist 2: Doesn't mention ice (their mechanism is mud and algae), so no impact. Scientist 3: Says "neither mud nor ice is responsible for the rocks’ movements"—their mechanism is tectonic activity. The finding is no seismic activity, which would weaken Scientist 3? Wait, no—the question is "no seismic activity was recorded". Scientist 3's explanation relies on tectonic activity (seismic - related). Scientist 1's explanation relies on ice. So:

Scientist 1: Needs ice to form. If no ice (because temp not cold enough), Scientist 1's explanation is weakened. Scientist 3: Needs tectonic activity (seismic - related). If no seismic activity, Scientist 3's explanation is weakened? Wait, no—the question is "this finding (no seismic activity) would weaken which of the scientists’ explanations?".

Wait, re - read Scientist 3: "The playa is located along a fault line between tectonic plates. Minor vertical shifts in the plates cause the rocks to move downhill...". So if there's no seismic activity (which would be related to tectonic plate movement), Scientist 3's explanation is weakened. Scientist 1: Explanation is about ice, mud, and light winds. No seismic activity doesn't affect ice formation (ice formation is about temperature). Wait, the finding is "no seismic activity was recorded in the playa where the trails left by the rocks are found". So:

• Scientist 1: Their explanation doesn't involve seismic activity, so no weakening.
• Scientist 2: Their explanation doesn't involve seismic activity, so no weakening.
• Scientist 3: Their explanation involves tectonic plate movement (which causes seismic activity), so no seismic activity weakens Scientist 3's explanation. Wait, but also, the first part: "no seismic activity"—Scientist 3's explanation needs tectonic movement (which causes seismic). So Scientist 3's explanation is weakened. But wait, the options: A is Scientist 1 only, B is Scientist 3 only, C is Scientist 1 and 2, D is Scientist 2 and 3.

Wait, maybe I made a mistake. Let's re - read the question: "Suppose that no seismic activity was recorded in the playa where the trails left by the rocks are found. This finding would weaken which of the scientists’ explanations?".

Scientist 1: Explanation is ice, mud, light winds. No seismic activity—doesn't affect. Scientist 2: Explanation is mud, algae, strong winds. No seismic activity—doesn't affect. Scientist 3: Explanation is tectonic plate movement (which causes seismic activity) and strong winds. So if there's no seismic activity, that suggests no tectonic movement, so Scientist 3's explanation is weakened. So the answer is B? Wait, but the options: B is Scientist 3 only. But wait, let's check again. Wait, maybe I misread Scientist 3's explanation. Scientist 3: "Water does collect in the playa, producing mud and ice. However, neither mud nor ice is responsible for the rocks’ movements. The playa is located along a fault line between tectonic plates. Minor vertical shifts in the plates cause the rocks to move downhill, leaving trails. Due to the combination of tectonic plate movement and strong winds, the rocks are able to move only a few meters over several years."

So if there's no seismic activity (which is a result of tectonic plate movement), then the tectonic plate movement (which causes the rocks to move) is not happening. So Scientist 3's expla…

Answer:

D. Mud and algae only

Question 2