Earth's Changing Surface — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Rivers carries sediment downstream and shape wide valleys over time.
Corrected: Rivers carry sediment downstream and shape wide valleys over time.
Grade 4 students learn rivers are powerful erosion agents, and plural subjects use base form verbs.
2. Fix the sentence:
Wind erosion in a desert form tall sand dunes from loose grains.
Corrected: Wind erosion in a desert forms tall sand dunes from loose grains.
Grade 4 NGSS includes wind erosion shaping deserts, and singular subjects take -s verb endings.
3. Fix the sentence:
Glaciers slowly carves U-shaped valleys as they move down mountains.
Corrected: Glaciers slowly carve U-shaped valleys as they move down mountains.
Grade 4 students learn glaciers carve U-shaped valleys, and plural subjects don't add -s to verbs.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. A river cutting deeper into its channel is an example of water erosion.
Grade 4 students identify water as the leading erosion agent, shaping canyons and river valleys.
2. Sand dunes in deserts are shaped mostly by wind erosion.
Grade 4 NGSS standards include wind erosion creating dunes in dry, plant-poor regions.
3. A slowly moving sheet of frozen water that carves valleys is called a glacier.
Grade 4 earth science uses glacier as the key vocabulary term for ice-driven erosion.
4. When loose rocks slide down a steep slope, the agent of erosion is gravity.
Grade 4 students learn gravity drives landslides and rockfalls, moving sediment downhill.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Describe how a glacier shapes the land as it moves downhill.
Sample answer: A glacier is a thick river of ice that drags rocks frozen into its base. As it slides, those rocks scrape and gouge the ground, carving wide U-shaped valleys and leaving piles of sediment when the ice melts.
Grade 4 NGSS explains glaciers as erosion agents that reshape landscapes through abrasion.
2. Why is wind erosion stronger in deserts than in forests?
Sample answer: Deserts have few plants and dry, loose sand, so wind picks up grains easily. Forests have many trees and roots that hold soil in place and slow the wind, so wind erosion is much weaker there.
Grade 4 students compare ecosystems to understand how vegetation reduces wind erosion.