Corrected sentences (pick one):
- Mountains are huge creases in the Earth's rocky coat.
- Mountains are big folds in the Earth's rocky crust.
- Mountains are big bumps on the Earth's rocky surface.
Why these changes?
- Earth's needs an apostrophe (') because it shows the rocky coat belongs to Earth.
- rocky-stony sounds odd and repeats the same idea. Use just rocky or stony, or say rocky, stony with a comma.
- on vs in: Mountains are part of the Earth's crust, so in the Earth's crust or on the Earth's surface both work. For kids, on the Earth's surface is easy to understand.
- coat is a poetic word. If you want a scientific word, use crust.
- Always start with a capital letter and end with a period: Mountains are ... .
Short explanation of mountains (for a 7-year-old): Mountains form when big pieces of the Earth push together and fold up, a bit like when you push a rug and it makes bumps.
If you want, try writing your favorite corrected sentence and I can check it for you!