Fast & Slow Earth Changes
Understand that Earth's surface can change quickly in an earthquake or eruption, while rock can also wear away little by little over many years
What a learner can do afterwards
- Give an example of a quick change to Earth's surface like a volcanic eruption
- Give an example of a slow change to Earth's surface like erosion by wind or water
- Compare quick and slow changes and explain the difference
1 · Read
Earth's surface can change at different speeds. An earthquake can shift or crack the ground in seconds. An eruption can cover land with lava or ash quickly. Some eruptions keep going for weeks or longer. Check how long the change took.
Waves can wear away a rocky cliff little by little over many years. Wind and water can carry away tiny rock pieces. These gradual changes are slow. Water can also change land quickly, such as when a flood washes soil away.
Compare the time taken. Ground shifting in seconds is quick. Rock wearing away over many years is slow. Quick changes may take seconds, minutes, hours, or days. A single picture of smooth rock does not tell you the time. Dated pictures or notes taken again and again can show how long a change took.
Use the time as a clue. Ground can shift in seconds, while rock can wear away little by little over many years.
Readings and flashcards written for this dataset. Earth-science resource records informed the facts and comparison activities; their prose is not reproduced.
More to read
After heavy ice melts
A thick ice sheet puts a heavy weight on the land beneath it. That weight can push the land down. When the ice melts, the weight is removed.
Some land then rises slowly. The rise can continue for many years. Watching the ground for a moment will not show such a small movement. Scientists compare measurements taken at different times to find it.
Keep a record of change
To compare changes, you need to know both what changed and how long it took. A note might record ground moving during a short earthquake. Photos taken over years might show a cliff getting smaller.
A smooth rock alone gives no date for its change. Records made at known times give better clues. Compare the same place or object so that a difference between two places is not mistaken for a change over time.
2 · Watch
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8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.