* They are all compounds: They are made up of two or more elements chemically bonded together.

* They are all found naturally: They occur in nature, although salt is often mined or extracted from the ocean.

* They are all essential to life: Water is crucial for hydration and biological processes. Carbon dioxide is used by plants for photosynthesis. Salt is an essential mineral for humans and animals.

* They all have a role in the Earth's systems: Water is a key component of the water cycle. Carbon dioxide is a greenhouse gas that plays a role in climate regulation. Salt influences the salinity of oceans and plays a role in geological processes.

While they are all important, they have some key differences:

* States of matter: Water can exist as a liquid, solid (ice), or gas (water vapor). Carbon dioxide is typically a gas at room temperature, although it can be solid (dry ice) under specific conditions. Salt is a solid.

* Chemical composition: Water is H₂O (two hydrogen atoms and one oxygen atom). Carbon dioxide is CO₂ (one carbon atom and two oxygen atoms). Salt is NaCl (one sodium atom and one chlorine atom).

Overall, water, carbon dioxide, and salt are all crucial components of the Earth's environment and have significant roles in maintaining life on our planet.