The lower density of ice compared to liquid water does not only mean that ice cubes float in your water cup. This property of water is important for life on Earth because both
all the water on Earth's surface, is an essential part of the Earth system. It interacts with
liquid water and ice are part of Earth's hydrosphere. The hydrosphere, which contains
the atmosphere and biosphere in many ways. For example, large pieces of floating ice
provide penguins, polar bears, and walruses with a resting place as they look for food in
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Water on Eart
the ocean.
3. Think about what happens in the hydrosphere and biosphere when ice forms at the
top of a lake. What might happen instead if ice were denser than liquid water?

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.