When a mutation has an effect that helps a species adapt to an environment, and specimens of both genders have it, it will end up taking over, causing evolution to gradually happen.
The polarity of the water molecule helps it to cohere to nearby water molecules, forming a skin over it.
The process by which molten material moves through the Earth's mantle is known as convection current. This is simply demonstrated within a liquid, in this case molten material, in which the hottest materials rise and the colder materials sink. Convection currents in the mantle are the forces that help move plate tectonics.
