Science You're Expected to Know · Lesson 5

Rocks, the atmosphere and the sky

Rocks come in three families. Igneous rock (such as basalt or granite) forms when melted rock cools. Sedimentary rock (such as sandstone, shale or limestone) forms from layers of sediment pressed together, and it is where fossils are usually found. Metamorphic rock forms when heat and pressure change existing rock.

In layers that haven’t been folded, tilted or overturned, each layer formed on top of the one below it, so lower layers are older. Fossils hint at the setting: seashells point to a sea, and land-plant leaves such as ferns point to land.

In the lower atmosphere, air temperature generally falls as altitude rises, which is why high mountains are cold. The passage will give you the actual numbers for that day.

In the sky, the Moon shines by reflected sunlight, and its phases come from how much of its sunlit half faces Earth as it orbits about once a month. Seasons come from the tilt of Earth’s axis, not from Earth’s distance to the Sun: the hemisphere tilted toward the Sun gets longer days and more direct sunlight, so it has summer while the other has winter.

A Mountain Field Trip

On one clear October morning, an Earth science class studied a mountain and the cliff at its base.

Study 1: At 9 a.m., students at five weather stations on the mountain recorded the air temperature in the shade. The stations were 0, 1, 2, 3 and 4 km above sea level (Figure 1).

Study 2: At the base of the mountain, a stream had cut a cliff that exposed four flat rock layers. No layer was folded, tilted, broken or overturned. Table 1 lists the layers from top (Layer 1) to bottom (Layer 4).

Figure 1
Figure 1Line graph of air temperature at 9 a.m. versus altitude. Temperature falls steadily as altitude rises: 16 °C at 0 km, 9.5 °C at 1 km, 3 °C at 2 km, −3.5 °C at 3 km and −10 °C at 4 km.-15-10-50510152001234Altitude (km)Air temperature (°C)
  • Air temperature
Show the data as a table
Figure 1: data
Altitude (km)Air temperature (°C)
016
19.5
23
3-3.5
4-10

Line graph of air temperature at 9 a.m. versus altitude. Temperature falls steadily as altitude rises: 16 °C at 0 km, 9.5 °C at 1 km, 3 °C at 2 km, −3.5 °C at 3 km and −10 °C at 4 km.

Table 1
LayerRockThickness (m)Fossils found
Layer 1 (top)Sandstone6None
Layer 2Shale4Fern leaves
Layer 3Limestone12Seashells
Layer 4 (bottom)Basalt (lava flow)3None
Rock layers from top to bottom. Layer 1: sandstone, 6 m thick, no fossils. Layer 2: shale, 4 m, fern leaves. Layer 3: limestone, 12 m, the thickest, seashells. Layer 4: basalt from a lava flow, 3 m, no fossils.

Worked example Easy

Show the whole passage

A Mountain Field Trip

On one clear October morning, an Earth science class studied a mountain and the cliff at its base.

Study 1: At 9 a.m., students at five weather stations on the mountain recorded the air temperature in the shade. The stations were 0, 1, 2, 3 and 4 km above sea level (Figure 1).

Study 2: At the base of the mountain, a stream had cut a cliff that exposed four flat rock layers. No layer was folded, tilted, broken or overturned. Table 1 lists the layers from top (Layer 1) to bottom (Layer 4).

Figure 1
Figure 1Line graph of air temperature at 9 a.m. versus altitude. Temperature falls steadily as altitude rises: 16 °C at 0 km, 9.5 °C at 1 km, 3 °C at 2 km, −3.5 °C at 3 km and −10 °C at 4 km.-15-10-50510152001234Altitude (km)Air temperature (°C)
  • Air temperature
Show the data as a table
Figure 1: data
Altitude (km)Air temperature (°C)
016
19.5
23
3-3.5
4-10

Line graph of air temperature at 9 a.m. versus altitude. Temperature falls steadily as altitude rises: 16 °C at 0 km, 9.5 °C at 1 km, 3 °C at 2 km, −3.5 °C at 3 km and −10 °C at 4 km.

Table 1
LayerRockThickness (m)Fossils found
Layer 1 (top)Sandstone6None
Layer 2Shale4Fern leaves
Layer 3Limestone12Seashells
Layer 4 (bottom)Basalt (lava flow)3None
Rock layers from top to bottom. Layer 1: sandstone, 6 m thick, no fossils. Layer 2: shale, 4 m, fern leaves. Layer 3: limestone, 12 m, the thickest, seashells. Layer 4: basalt from a lava flow, 3 m, no fossils.

Based on Table 1, which layer formed first?

  1. Layer 1
  2. Layer 2
  3. Layer 3
  4. Layer 4Answer

How to solve it

  1. From the passage: the layers are flat and undisturbed; Layer 4 is at the bottom.
  2. From background: in undisturbed layers, lower means older.
  3. Layer 4 formed first.

Why each choice is right or wrong

  • A. Incorrect. Layer 1 is on top, so it formed last. The top layer is the youngest, not the oldest.
  • B. Incorrect. Fern leaves tell you about the setting, not the age order. Layer 2 sits above Layers 3 and 4, so it is younger than both.
  • C. Incorrect. Layer 3 is the thickest, at 12 m, but thickness doesn’t show age; position does.
  • D. Correct. Table 1 lists Layer 4 at the bottom, and the passage says no layer was folded, tilted or overturned. From background, in undisturbed layers the lowest is oldest.

Worked example Medium

Show the whole passage

A Mountain Field Trip

On one clear October morning, an Earth science class studied a mountain and the cliff at its base.

Study 1: At 9 a.m., students at five weather stations on the mountain recorded the air temperature in the shade. The stations were 0, 1, 2, 3 and 4 km above sea level (Figure 1).

Study 2: At the base of the mountain, a stream had cut a cliff that exposed four flat rock layers. No layer was folded, tilted, broken or overturned. Table 1 lists the layers from top (Layer 1) to bottom (Layer 4).

Figure 1
Figure 1Line graph of air temperature at 9 a.m. versus altitude. Temperature falls steadily as altitude rises: 16 °C at 0 km, 9.5 °C at 1 km, 3 °C at 2 km, −3.5 °C at 3 km and −10 °C at 4 km.-15-10-50510152001234Altitude (km)Air temperature (°C)
  • Air temperature
Show the data as a table
Figure 1: data
Altitude (km)Air temperature (°C)
016
19.5
23
3-3.5
4-10

Line graph of air temperature at 9 a.m. versus altitude. Temperature falls steadily as altitude rises: 16 °C at 0 km, 9.5 °C at 1 km, 3 °C at 2 km, −3.5 °C at 3 km and −10 °C at 4 km.

Table 1
LayerRockThickness (m)Fossils found
Layer 1 (top)Sandstone6None
Layer 2Shale4Fern leaves
Layer 3Limestone12Seashells
Layer 4 (bottom)Basalt (lava flow)3None
Rock layers from top to bottom. Layer 1: sandstone, 6 m thick, no fossils. Layer 2: shale, 4 m, fern leaves. Layer 3: limestone, 12 m, the thickest, seashells. Layer 4: basalt from a lava flow, 3 m, no fossils.

Based on Figure 1, at about what altitude was the air temperature 0 °C?

  1. Between 0 km and 1 km
  2. Between 1 km and 2 km
  3. Between 2 km and 3 kmAnswer
  4. Between 3 km and 4 km

How to solve it

  1. From the passage: read the temperature at each station: 16, 9.5, 3, −3.5 and −10 °C.
  2. Find where the sign changes: 3 °C at 2 km and −3.5 °C at 3 km.
  3. 0 °C lies between 2 km and 3 km, about halfway.

Why each choice is right or wrong

  • A. Incorrect. The temperatures there are 16 °C and 9.5 °C, both well above 0 °C.
  • B. Incorrect. The temperatures there are 9.5 °C and 3 °C, still above 0 °C.
  • C. Correct. Figure 1 shows 3 °C at 2 km and −3.5 °C at 3 km (passage), so the line crosses 0 °C between them, near 2.5 km.
  • D. Incorrect. At 3 km the air was already below freezing, at −3.5 °C, so 0 °C comes lower down.

Trap A remembered number isn’t the passage’s number

You may have learned a typical rate for how fast air cools with height, or a rule of thumb for which rock is oldest. On test day, the figure is the authority: read the temperatures that the students recorded, and use the layer order that the table gives. Use background knowledge to understand the passage, then let the data decide the answer.