The upper layers of water in a deep well are cool but those in a pond are warm
Answers
Explanation:
It’s because water is a very unusual substance. It contracts and becomes denser as it gets colder, like most liquids, but only down to 4C. It then starts expanding, and as we all know ice floats on water.
A pond in winter will actually be colder on top; ice, and water colder than 4C, will float on the underlying water at 4C. There won’t be any convection currents to mix the water, so cooling is a very slow process from the top down. Before the pond can freeze all the way down, Spring arrives.
Come Spring, and heat transfers from the air and sun above to the surface of the pond. The ice melts. The surface water warms from below 4C to above 4C, at no point becoming denser than the underlying water at 4C so convection does not mix warmer water on top with the underlying water. So the pond can only warm slowly from the top down …
And before it does, Winter is back.
If ice sank in liquid water like the solid phase of most materials does in the liquid phase, oceans would be thin skins of seasonally liquid water sitting on top of kilometers of ice, and life would in all likelyhood not ever have got started.