Why are some cliffs white?
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Answer: Made of chalk or limestone
Made of chalk or limestone ✓ — Correct! White cliffs (like Dover) are made of chalk—soft white limestone formed from compressed microscopic marine organisms (coccolithophores) over millions of years. When these calcium carbonate-rich organisms died, they accumulated on ancient seabeds. Tectonic uplift raised them, erosion exposed them. Pure white calcium carbonate creates the distinctive color!
Bird droppings accumulate — Wrong. Droppings don't create white cliffs (though they may add stains!). Cliffs are white because they're made of chalk/limestone rock.
Bleached by sunlight — Wrong. Sunlight doesn't bleach rock. White cliffs are naturally white because they're composed of calcium carbonate (chalk/limestone).