Mystery #2Tier 1rivers and erosion
Why are pebbles in a river so smooth and round when mountain rocks are jagged?
Up in the mountains, the rocks are rough and jagged, all sharp points and broken edges. Yet the pebbles in the river below are smooth and round enough to hold like an egg. They are made of the same stuff, so something must have changed them. Why is a river pebble so smooth and round?
Your guess
What is your best idea? What made that pebble so smooth and round?
There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.
Make a guess to unlock the hints and the answer.