Earth and its system components

Where the answer comes from: the passage says "At a divergent boundary, plates move apart. Magma rises to fill the gap," often forming "an underwater mountain range called a mid-ocean ridge." In the diagram, the arrows on both sides of X point away from X, and a dashed magma line rises beneath it.

Step by step:

1. Read the arrows: the plate left of X moves left; the plate right of X moves right. They move apart.
2. X is an underwater ridge with magma rising, exactly as the passage describes.
3. Plates moving apart = divergent.

The boundary at X is divergent.

Tip: Link each boundary to its motion: divergent = divide (apart), convergent = converge (together), transform = slide past.

Where the answer comes from: the passage says water "escapes into the air as water vapor through tiny pores, a process called transpiration." The leafy bag collected 4.2 mL, while the bag around a bare stick collected only 0.3 mL.

Step by step:

1. The bag was sealed, so no rain could get in. That rules out precipitation.
2. The leafy branch is the only source that the bare-stick bag did not have.
3. Water traveled from the roots up to the leaves and left the leaves as vapor: transpiration.
4. The vapor then condensed into droplets on the cooler inside of the bag. Condensation formed the droplets, but transpiration supplied the vapor.

The answer is transpiration.

Check: The extra water in the leafy bag is 4.2 - 0.3 = 3.9 mL, which came from the plant ✓.

Tip: Read the question's exact wording. Put vapor into the bag asks for the source of the vapor, not how the droplets formed.

Where the answer comes from: the passage says "Air pressure tells how much air lies above a place," and the table shows that at 5.5 km the pressure is 50% of sea-level pressure.

Step by step:

1. At sea level (0 km), pressure is 100%: all of the atmosphere's air is above you.
2. At 5.5 km, pressure is 50%: half of the air is still above you.
3. So the other half must be below 5.5 km.

About half of the atmosphere's air lies below 5.5 km.

Check: This fits the passage: gravity holds most air close to Earth, so a big share is packed into the lowest few kilometers, even though the atmosphere extends past 50 km ✓.

Tip: When a table gives a percent of a total, ask what the rest of the total is. Many questions ask about the part not shown.

Where the answer comes from: the passage says "In the stratosphere, the ozone layer absorbs ultraviolet (UV) light from the Sun. This warms the air, so temperature rises with altitude." On the graph, temperature rises from about −56.5 °C at 20 km to about −2.5 °C near 47–51 km, inside the stratosphere band.

Step by step:

1. Find layers where the line moves right (warmer) as you go up: the stratosphere and the thermosphere.
2. Check the cause: the passage links the stratosphere's warming to ozone absorbing UV. It links the thermosphere's warming to thin air absorbing high-energy radiation, not to ozone.
3. Only the stratosphere matches both parts of the question.

The answer is the stratosphere.

Tip: When a question has two conditions, check every choice against both. Here the thermosphere meets only one.

Where the answer comes from: the passage gives 15 °C at sea level and −56.5 °C at 11 km, the top of the troposphere.

Step by step:

1. Rate of cooling: \frac{15 - (-56.5)}{11} = \frac{71.5}{11} = 6.5\ ^\circ\text{C per km}
2. Cooling over 8.8 km: 6.5 \times 8.8 = 57.2\ ^\circ\text{C}
3. Start at 15 °C and subtract: 15 - 57.2 = -42.2\ ^\circ\text{C}

The summit temperature is about −42 °C.

Check: 8.8 km is a bit below 11 km, so the answer should be a bit warmer than −56.5 °C. −42 °C fits ✓

Tip: When you use a rate to predict, start from the known value (15 °C) and apply the change. Then check that the answer falls in a sensible range on the graph.

Where the answer comes from: Table 1 is labeled "30-year averages, 1991–2020" and lists City Q's average July air temperature as 27 °C. The weather report describes what happened "July 12 of last year."

Step by step:

1. Weather = short-term conditions at a certain time and place (today's storm, a heat wave, tomorrow's fog).
2. Climate = the average pattern over many years, usually 30 years.
3. The heat wave, the thunderstorm, and tomorrow's fog are each a single event or forecast, so they are weather.
4. The 30-year average July temperature describes the long-term pattern, so it is climate.

The answer is City Q's average July air temperature over 30 years is 27 °C.

Tip: Look for time words. Average, usually, over 30 years signal climate; today, on July 12, tomorrow signal weather.

Where the answer comes from: Table 1 lists 30 s → 240 km and 50 s → 400 km, with every 10 seconds adding 80 km (10 → 80, 20 → 160, 30 → 240).

Step by step:

1. Find the pattern: distance = 8 km for each second of gap (80 \div 10 = 8).
2. Apply it to 40 seconds: 40 \times 8 = 320 \text{ km}
3. Check with the table: 40 s lies halfway between 30 s (240 km) and 50 s (400 km), and halfway between 240 and 400 is 320 ✓

The station is about 320 km from the epicenter.

Tip: When a value falls between two rows, find the pattern (or the midpoint) instead of copying the nearest row.

Where the answer comes from: the table shows mean sediment carried out of the tray: 40 g at 5°, 95 g at 10°, 160 g at 15° and 240 g at 20°.

Step by step:

1. The slope (independent variable) goes up from 5° to 20°.
2. The sediment carried out (dependent variable) goes up every time: 40 → 95 → 160 → 240 g.
3. A steeper slope makes water flow faster, and faster water can pick up and carry more sediment. That is more erosion.

The answer is as the slope increased, the amount of sediment the water eroded and carried out increased.

Check: The increase gets bigger at each step (55 g, then 65 g, then 80 g), so the effect grows stronger at steeper slopes. Nothing in the data shows it leveling off ✓.

Tip: Describe a relationship by naming both variables and the direction: as X increased, Y increased.

Where the answer comes from: the passage says "The hot spot stays in about the same place while the tectonic plate above it slowly moves," building a chain of islands "that get older in the direction the plate is moving." It also says islands farther from the hot spot "lie farther to the northwest."

Step by step:

1. A new volcano always forms over the fixed hot spot (Island V today).
2. The plate carries each finished island away from the hot spot.
3. The longer ago an island formed, the farther it has been carried.
4. The older islands lie to the northwest, so the plate must be moving toward the northwest.

The answer is the plate is moving northwest over a hot spot that stays in place.

Check: If the hot spot moved northwest under a still plate, the newest island would be in the northwest, the opposite of the data ✓.

Tip: In hot-spot questions, the youngest island marks the hot spot, and the line of older islands points the way the plate is going.

Where the answer comes from: the passage says "a feature that cuts across rock layers is younger than the layers it cuts." In the diagram, dike F cuts through layers A, B, C, D and E and reaches the ground surface.

Step by step:

1. By superposition, E is the youngest layer.
2. But dike F cuts through E, so the magma must have pushed in after E was already there.
3. Fault G cuts only A–D and stops at the unconformity under E, so it is older than E.
4. Therefore the dike is younger than everything else in the diagram.

The youngest feature is dike F.

Check: Nothing in the diagram cuts across the dike, so no feature is younger than it ✓.

Tip: The top layer is the youngest layer, but not always the youngest thing. Always check for faults or dikes that cut the top layer.

Where the answer comes from: the passage says "The farther away the station is, the longer the time between the two arrivals," and "each second of S–P interval means the epicenter is about 8 km away." The table gives Brook 12 s (96 km) and Corley 40 s (320 km); Ashford's interval is 25 s.

Step by step:

1. Find Ashford's distance: 8 km for each second of lag, so 25 \times 8 = 200 km.
2. Compare the distances: Brook 96 km, Ashford 200 km, Corley 320 km.
3. The smallest distance (and the shortest S–P interval, 12 s) belongs to Brook.

The closest station is Brook, about 96 km away.

Check: 12 \times 8 = 96 ✓, which matches the table.

Tip: In S–P questions, shorter gap = closer. Do not mix up the seconds column with the kilometers column.

Where the answer comes from: the table rows "| Pine Ridge | West slope | 1,500 | 1,900 |" and "| Dry Creek | East slope | 1,500 | 380 |".

Step by step:

1. If elevation alone controlled precipitation, towns at the same elevation would get about the same precipitation.
2. Pine Ridge and Dry Creek are both at 1,500 m, but Pine Ridge gets 1,900 mm and Dry Creek gets only 380 mm.
3. Also, Dry Creek (1,500 m) is much drier than Westport (10 m), even though it is far higher.
4. The difference is the side of the range: the east slope is in the rain shadow.

The best evidence: Dry Creek and Pine Ridge are at the same elevation, but Dry Creek gets about one-fifth as much precipitation.

Tip: The word always can be disproved by one clear counterexample. Look for one case that breaks the rule.

Where the answer comes from: Table 1: 20 s → 160 km. The passage: "A time gap tells scientists only how far away the epicenter is, not in which direction," and "The epicenter is where the circles from at least three stations meet."

Step by step:

1. Read the table: a 20-second gap means the epicenter is 160 km from Station A.
2. Direction is unknown, so the epicenter could be anywhere on a circle of radius 160 km around Station A.
3. A second station's circle usually crosses the first circle at two points, which still leaves two possible spots. A third circle picks one point. That is why the passage says at least three stations.
4. The time gap says nothing about magnitude; magnitude depends on the size of the shaking.

The correct statement is that the epicenter is 160 km from Station A, and data from at least two more stations are needed to locate it.

Tip: Keep track of exactly what one measurement can tell you. Distance is not location, and timing is not strength.

Where the answer comes from: the passage says "where the water spread into a pool at the bottom end, it slowed down. Gravel settled first, close to where the water entered the pool, and fine sand settled farther out." It defines deposition as "the dropping of sediment when the water, wind or ice slows down."

Step by step:

1. When the river enters the calm lake, the water slows down, just like in the model's pool.
2. Slower water cannot carry heavy particles, so the biggest, heaviest pieces (gravel) drop first, near the river mouth.
3. Smaller pieces (sand) are carried a little farther.
4. The finest particles (mud) stay in the water longest and settle farthest out in the lake.

The answer is gravel near the river mouth, sand farther out, and fine mud farthest into the lake.

Tip: Apply a model by matching its parts to the real case: tray = river, pool = lake. Then use the same cause (slowing water) to predict the effect.

Where the answer comes from: the table gives 1,319 earthquakes per year of magnitude 5.0–5.9 and 15 per year of magnitude 7.0–7.9.

Step by step:

1. To compare how common they are, divide: \frac{1{,}319}{15} \approx 88
2. So magnitude 5 earthquakes are about 88 times as common as magnitude 7 earthquakes.

The answer is about 88 times.

Check: Each step of 1.0 makes earthquakes roughly 9 to 10 times less common in the table (1,319 → 134 → 15), and 9 \times 10 \approx 90 ✓.

Tip: How many times as many means divide. How many more means subtract. Read which one the question asks for.

Where the answer comes from: the passage says "Water warms up and cools down more slowly than land, so places near an ocean usually have milder winters and cooler summers than places far inland." It also says the cities are "at the same latitude (41° N) and almost the same elevation."

Step by step:

1. List the climate factors: latitude, elevation, nearness to water, ocean currents.
2. Latitude and elevation are the same for both cities, so they cannot explain a difference.
3. Port Harlow is on the coast; Dunmore is 900 km inland. That factor is different.
4. The ocean warms slowly in summer and cools slowly in winter, keeping Port Harlow's air milder in both seasons. Dunmore heats up and cools down much more.

The best explanation is Port Harlow is next to the ocean, which heats and cools more slowly than land.

Tip: To explain a difference, the cause must itself be different between the two cases. A factor that is the same for both cannot explain why they differ.

Where the answer comes from: the passage says the students "sealed an identical bag around a bare wooden stick of the same size in a second pot with the same moist soil," and that "Both pots sat in the same sunny window." It collected 0.3 mL, compared with 4.2 mL in the leafy bag.

Step by step:

1. Some water could collect in any sealed bag, for example from moisture already in the air inside it.
2. The stick bag has everything the leafy bag has (same bag, soil, light, time) except a living, leafy plant.
3. So it is a control: it shows how much water collects without transpiration.
4. The difference, 4.2 - 0.3 = 3.9 mL, can then be credited to transpiration from the leaves.

The purpose was to show how much water collects without a living plant, so the extra water in the leafy bag could be credited to transpiration.

Tip: A control group matches the experimental group in every way except the variable being tested. Its result is the baseline you subtract or compare against.

Where the answer comes from: the table: 40 g at 5°, 95 g at 10°, 160 g at 15°, 240 g at 20°.

Step by step:

1. Find the increase for each 5° step: 95 - 40 = 55, 160 - 95 = 65, 240 - 160 = 80 g.
2. The increases are getting larger (55, 65, 80), so the next increase should be at least about 80 g, probably a bit more.
3. 240 + 80 = 320 g, or slightly more.
4. About 320 g is the best estimate. 240 g would mean no increase, and 600 g would be a jump far bigger than any in the data.

The best prediction is about 320 g.

Check: The answer must be more than 240 g because sediment rose at every step ✓.

Tip: To extend a trend, look at the change between data points, not just the values. Growing changes mean the next change will be at least as large.

Where the answer comes from: the map shows both cities on the same dashed line at 37° N and a "Cold current (from polar waters)" flowing past City P. Table 1 shows July sea-surface temperature of 14 °C at City P vs. 26 °C at City Q, and July air temperature of 19 °C vs. 27 °C. The passage says "Air above the ocean takes on the water's temperature."

Step by step:

1. Rule out latitude: both cities are at 37° N, so they get the same summer sunlight. Latitude cannot explain the difference.
2. Link the current to the water: City P's coastal water is 12 °C colder, which fits a current flowing from polar waters.
3. Link the water to the air: air takes on the water's temperature, and City P's July air is 8 °C cooler.
4. Only one choice uses both sources and rules out the main alternative.

The best evidence is same latitude, plus much colder sea-surface water next to a current from polar waters.

Tip: Strong support for a cause does two jobs: it connects the cause to the effect, and it rules out a competing explanation.

Where the answer comes from: the table lists each town's side, elevation and precipitation, for example "| Pine Ridge | West slope | 1,500 | 1,900 |" and "| Dry Creek | East slope | 1,500 | 380 |".

Step by step:

1. To test the side of the range, pick two towns on different sides but at the same elevation, so elevation is controlled.
2. Pine Ridge (west slope) and Dry Creek (east slope) are both at 1,500 m.
3. Pine Ridge gets 1,900 mm; Dry Creek gets 380 mm. With elevation held equal, the big difference must come from something else, here the rain shadow on the east side.
4. The other pairs change elevation too, or are on the same side.

The best pair is Pine Ridge and Dry Creek.

Tip: On the GED, the best evidence for one cause comes from cases that are alike in every other important way. Find the pair that differs in only one variable.

Where the answer comes from: the passage says each increase of 1.0 means "about 32 times more energy is released and about 10 times larger ground shaking (wave amplitude)."

Step by step:

1. From 4.5 to 6.5 is 2 whole steps.
2. Amplitude: 10 \times 10 = 100 times larger.
3. Energy: 32 \times 32 = 1{,}024, about 1,000 times more.

The correct statement is A's ground shaking is about 100 times larger, and A releases about 1,000 times more energy.

Check: Adding instead of multiplying would give 10 + 10 = 20 and 32 + 32 = 64. Those are the traps in the other choices ✓.

Tip: On power scales, factors multiply. Keep the two factors (10 for amplitude, 32 for energy) separate.

Where the answer comes from: the table pairs distance and age: "| W | 160 | 2.0 |", "| X | 320 | 4.0 |", "| Y | 480 | 6.0 |", "| Z | 640 | 8.0 |" (distance in km, age in millions of years).

Step by step:

1. Steady speed means the plate covers the same distance in each equal period of time.
2. Each extra 160 km of distance goes with an extra 2.0 million years of age.
3. So every island gives the same speed: 160 \div 2.0 = 320 \div 4.0 = 480 \div 6.0 = 640 \div 8.0 = 80 km per million years.
4. The heights of the islands tell how much they have sunk and eroded, not how fast the plate moved.

The best support is each additional 160 km of distance matches an additional 2.0 million years of age.

Tip: To support a claim about a rate, choose evidence that uses both quantities in the rate (here, distance and time).

Where the answer comes from: the passage says "One station can tell how far away the epicenter is, but not in which direction," and "Two circles usually cross at two points. A circle from a third station passes through only one of those points, and that point is the epicenter."

Step by step:

1. Brook's data put the epicenter somewhere on a circle of radius 96 km around Brook.
2. Corley's data put it on a circle of radius 320 km around Corley.
3. These two circles usually cross at two points, so there are still two possible epicenters.
4. Ashford's circle (radius 25 \times 8 = 200 km) passes through only one of those two points. That point is the epicenter.

The answer is two circles usually cross at two points, and the third circle shows which point is the epicenter.

Tip: Triangulation needs three distances because each distance gives only a circle of possible locations.

Where the answer comes from: the passage says "a feature that cuts across rock layers is younger than the layers it cuts," and an unconformity "marks a time when rock was worn away before new layers were laid down on top."

Step by step:

1. The fault cuts layer D, so D already existed when the fault moved. The fault is younger than D.
2. The fault does not cut layer E, so E was laid down after the fault stopped moving. The fault is older than E.
3. The fault also stops at the unconformity, so erosion planed off the broken surface before E was deposited.
4. So the fault moved after D was deposited and before E was deposited.

The answer is the fault moved after layer D was deposited but before layer E was deposited.

Check: In the diagram, the right side of the fault dropped down, but layer E lies smoothly across both sides, with a thicker part filling the low side. That only makes sense if E came later ✓.

Tip: A feature that cuts some layers but not others is sandwiched in time between the last layer it cuts and the first layer it does not cut.