Water exhibits unique properties, particularly in its density, which significantly influences its behavior in different states. In its liquid form, water molecules are closely packed, resulting in a high density. These molecules are in constant motion, forming and breaking hydrogen bonds. Conversely, when water freezes into ice, the molecules arrange themselves into a stable lattice structure, which causes them to expand and occupy more space. This arrangement leads to a lower density in solid ice compared to liquid water.

The lower density of ice is crucial because it allows ice to float on liquid water. This phenomenon is vital for sustaining life, as it means that bodies of water freeze from the top down. The ice layer that forms on the surface acts as an insulator, protecting the liquid water beneath from freezing completely. This insulation is essential for aquatic life, especially during extreme temperature fluctuations, such as those experienced during ice ages. Without this property, oceans could have frozen solid, threatening the survival of many species.

To visualize this concept, consider the comparison between the two states of water. In liquid form, water molecules are densely packed, while in solid form, they are arranged in a less dense lattice structure. This difference in density is a fundamental characteristic of water that plays a critical role in ecological systems and the survival of life on Earth.