Forces that build land up and wear it down
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
Read this first
Model card (example data)
Crust 2.7 g/cm³ floats on mantle 3.3 g/cm³. As rock is removed, the crust floats up by 2.7/3.3 of the thickness removed.
A student says removing 3,300 m of rock lowers a range's peaks by 3,300 m. Milo uses the model card. What is the net lowering?
- About 3,300 m, since peaks drop by the thickness eroded
- The peaks rise 2,700 m, since erosion lifts the crust
- About 600 m, since the crust rebounds about 2,700 m as the load is removed
- About 2,700 m, since the rebound is the lowering
A student says a range rising 1 cm a year (USGS) will be 100 km taller in 10 million years. Luz checks the claim. What is its main flaw?
- Mountains cannot rise, since weathering wins over uplift in the long run
- It ignores erosion and changing rates over millions of years
- Uplift slows when erosion piles sediment on the peaks
- The rate is too small: 1 cm a year adds just 10 km in 10 million years, not 100 km
A, 0.04, 0.04, 60 cm, steady; B, 0.04, 0.25, bare rock; C, 0.04, 0.01, 120 cm, thickening. A student claims weathering and erosion always run at the same rate. Jun checks the table. Which reply fits?
- Yes: sites A and C both hold soil, so their rates must be equal
- No: weathering moves soil away at sites B and C, which leaves rock bare
- Yes: soil is made at 0.04 mm a year everywhere, so erosion must match it
- No: they match only at site A; site B is bare and site C is deepening
Model card (example data)
Crust 2.7 g/cm³ floats on mantle 3.3 g/cm³. As rock is removed, the crust floats up by 2.7/3.3 of the thickness removed.
Erosion removes 20 m of rock per million years from a range. Bo uses the model card. How long to lower its peaks by 600 m?
- About 30 million years
- About 165 million years
- About 37 million years
- About 1.65 million years
Sea-floor limestone now lies 2,700 m up. Noah weighs two explanations: the land rose, or the sea once stood that high. Which evidence would best decide?
- A date showing the limestone formed on the sea floor
- The same marine layer lies at sea level on a coast 300 km away
- More marine fossils found in the plateau rock, of many kinds and ages
- Limestone layers that lie flat
A catchment was logged in 2015. Ren designs a test of whether erosion there has increased. Which measurement is most informative?
- Soil depth measured at one hilltop after logging
- Sediment past a gauge before and after, in years with matching rainfall
- Sediment carried past the gauge after logging, measured in one very wet year
- Rainfall totals measured before and after logging
A study measures 0.2 mm a year of erosion at one rock outcrop. A writer claims the whole range erodes at that rate. Tala grades the claim. What is the best verdict?
- Strongly supported: a measured rate applies everywhere in a range
- Not supported: erosion rates cannot be measured
- Weakly supported: one outcrop cannot represent a varied range
- Supported: a precise measurement at one place is precise everywhere
Three sites (example data)
Site Uplift (mm/yr) Erosion (mm/yr) Height trend P 5 5 steady Q 0 1 falling R 6 2 rising Zee reads the table. Which summary of what sets height fits all three sites?
- Height follows erosion alone, so R at 2 mm a year is the lowest site
- Height follows uplift alone, so P at 5 mm a year must be rising
- Height follows uplift minus erosion: steady at P, falling at Q, rising at R
- Height follows whichever rate is larger, so P is falling
Table, Three climates (example data), with columns Site, Mean temperature (°C), Rain (mm/yr), Weathering seen
Alpine, -2, 900, frost-split blocks, little clay; Rainforest, 25, 3,000, deep clay soil, few fragments; Desert, 22, 100, thin rock crumbs, little clay.
Esme reads the table. Which summary of weathering fits all three sites?
- Cold sites favor physical breakup; warm, wet sites favor chemical change
- Warmth alone drives chemical weathering, since the 22 °C desert made clay
- The three sites show chemical weathering at the same rate
- Wet sites break rock into blocks, while cold sites turn it to clay
Ari runs uplift of 0.5 mm a year against erosion of 0.4 mm a year for 10 million years (example data). Which summary fits?
- Net gain is 9,000 m, since both processes move rock
- Net gain is 1,000 m, the gap between 5,000 m and 4,000 m, so a 10% error in erosion shifts it by 400 m
- Net gain is 1,000 m, and a small rate error cannot change it much
- Net gain is 5,000 m, the larger total, whatever the erosion rate