How can fossils be used to determine a relationship between living species and extinct ones?

Fossils are significant in showing the evolution of species. Fossils can be used to determine features that are shared between the current living organisms and ancient organism which they are related. This can be used to study how organisms evolve and how this is related to the ecological conditions of the time compared to now. Organisms evolve so they can adapt to a changing habitat.  

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answer: ice crystals in air

the water from the water body or another source of water gets evaporated as water vapor as an effect of heat on water. these water vapor rises in the upper layers of the earth atmosphere under high atmospheric pressure. the atmospheric pressure of these water molecules starts to decrease due to the effect of cold air. the invisible water vapor condenses into visible water droplets and ice crystals.these ice crystals and water droplets being less denser than the surrounding air floats on air as clouds.