Forces that build land up and wear it down
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
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?
- 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
- It ignores erosion and changing rates over millions of years
- Mountains cannot rise, since weathering wins over uplift in the long run
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: 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
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 0.8 mm a year
- About 0.3 mm a year
- About 2.1 mm a year
- About 0.3 m a year
Read this first
River terraces above a river (example data)
Terrace Height above river (m) Age (million years) Lower 40 0.8 Upper 100 1.6 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: 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
- It slowed: 100 m per million years at first, then 40 m
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?
- More marine fossils found in the plateau rock, of many kinds and ages
- The same marine layer lies at sea level on a coast 300 km away
- Limestone layers that lie flat
- A date showing the limestone formed on the sea floor
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 carried past the gauge after logging, measured in one very wet year
- Rainfall totals measured before and after logging
- Sediment past a gauge before and after, in years with matching rainfall
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
- 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
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 uplift minus erosion: steady at P, falling at Q, rising at R
- 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 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?
- 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
- The three sites show chemical weathering at the same rate
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, 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 9,000 m, since both processes move rock
- Net gain is 5,000 m, the larger total, whatever the erosion rate