Forces that build land up and wear it down

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 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.

2. 1.

   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
   • About 600 m, since the crust rebounds about 2,700 m as the load is removed
   • The peaks rise 2,700 m, since erosion lifts the crust
   • About 2,700 m, since the rebound is the lowering
3. 2.

   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?

   • No: they match only at site A; site B is bare and site C is deepening
   • Yes: soil is made at 0.04 mm a year everywhere, so erosion must match it
   • 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

4. 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.

5. 3.

   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 1.65 million years
   • About 30 million years
   • About 165 million years
   • About 37 million years
6. 4.

   Kira studies a basin of 2,000 km² that loses 1.6 million tonnes of rock a year (rock is 2.6 tonnes per m³; example data). What is the average lowering per year?

   • About 0.3 m a year
   • About 2.1 mm a year
   • About 0.8 mm a year
   • About 0.3 mm a year

7. River terraces above a river (example data)

   Terrace	Height above river (m)	Age (million years)
   Lower	40	0.8
   Upper	100	1.6

8. 5.

   Pia compares incision rates. How did the river's cutting rate change from 1.6 to 0.8 million years ago and since?

   • It stayed constant at 62.5 m per million years, the overall average
   • It slowed: 100 m per million years at first, then 40 m
   • It sped up: 50 m per million years at first, then 75 m
   • It slowed: 75 m per million years before 0.8 million years ago, then 50 m
9. 6.

   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
   • Rainfall totals measured before and 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
10. 7.

    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
    • Supported: a precise measurement at one place is precise everywhere
    • Weakly supported: one outcrop cannot represent a varied range
    • Not supported: erosion rates cannot be measured

11. 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

12. 8.

    Zee reads the table. Which summary of what sets height fits all three sites?

    • 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
    • Height follows erosion alone, so R at 2 mm a year is the lowest site

13. 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.

14. 9.

    Esme reads the table. Which summary of weathering fits all three sites?

    • The three sites show chemical weathering at the same rate
    • Wet sites break rock into blocks, while cold sites turn it to clay
    • Warmth alone drives chemical weathering, since the 22 °C desert made clay
    • Cold sites favor physical breakup; warm, wet sites favor chemical change
15. 10.

    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 1,000 m, and a small rate error cannot change it much
    • 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 9,000 m, since both processes move rock
    • Net gain is 5,000 m, the larger total, whatever the erosion rate