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 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?

   • The rate is too small: 1 cm a year adds just 10 km in 10 million years, not 100 km
   • Uplift slows when erosion piles sediment on the peaks
   • Mountains cannot rise, since weathering wins over uplift in the long run
   • It ignores erosion and changing rates over millions of years
4. 3.

   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: 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
   • Yes: sites A and C both hold soil, so their rates must be equal
   • No: they match only at site A; site B is bare and site C is deepening

5. 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.

6. 4.

   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 1.65 million years
   • About 37 million years
   • About 165 million years
7. 5.

   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

8. River terraces above a river (example data)

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

9. 6.

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

   • It sped up: 50 m per million years at first, then 75 m
   • It slowed: 100 m per million years at first, then 40 m
   • It slowed: 75 m per million years before 0.8 million years ago, then 50 m
   • It stayed constant at 62.5 m per million years, the overall average
10. 7.

    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
    • Limestone layers that lie flat
    • More marine fossils found in the plateau rock, of many kinds and ages
11. 8.

    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
    • Rainfall totals measured before and after logging
    • Sediment carried past the gauge after logging, measured in one very wet year
12. 9.

    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?

    • 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
    • Strongly supported: a measured rate applies everywhere in a range

13. 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

14. 10.

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

    • Height follows uplift minus erosion: steady at P, falling at Q, rising at R
    • Height follows uplift alone, so P at 5 mm a year must be rising
    • 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