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:
Physical weathering happen when ice freezes inside rock cracks.
Corrected: Physical weathering happens when ice freezes inside rock cracks.
Grade 4 students learn ice wedging is physical weathering, and the singular subject takes the -s verb form.
2. Fix the sentence:
Acid rain dissolve the limestone on old statues slowly.
Corrected: Acid rain dissolves the limestone on old statues slowly.
Acid rain causing chemical weathering is a Grade 4 NGSS example, and singular subjects need verbs ending in -s.
3. Fix the sentence:
Tree roots growing into cracks breaks rocks apart over time.
Corrected: Tree roots growing into cracks break rocks apart over time.
Biological weathering by plant roots is a Grade 4 concept, and plural subjects use the base verb form.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. When water freezes inside a rock crack, it expands and causes physical weathering.
Grade 4 students learn ice wedging is a physical weathering process that fractures rocks mechanically.
2. Acid rain reacting with limestone to dissolve it is an example of chemical weathering.
Grade 4 NGSS standards include chemical weathering, where substances alter rock composition.
3. Tree roots pushing into stone cracks is called biological weathering.
Grade 4 earth science recognizes biological weathering as breakdown caused by organisms.
4. All weathering processes work to break down rocks into smaller pieces called sediment.
Grade 4 students learn weathered rock becomes sediment, which connects to deposition later.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Explain how freezing water can crack a large rock over many winters.
Sample answer: Water seeps into tiny rock cracks, then freezes and expands about 9 percent. The ice pushes the crack walls apart. After many freeze-thaw cycles, the crack grows until the rock splits.
Grade 4 students explain ice wedging as a physical weathering mechanism driven by water's expansion when frozen.
2. Give one example of biological weathering you might see near your school.
Sample answer: Tree roots growing under a sidewalk can crack the concrete as they push upward. Mosses and lichens on rocks also release weak acids that slowly break the rock surface.
Grade 4 NGSS encourages observing local examples of biological weathering by plants and organisms.