Which term encompasses all the water present on Earth?

The term that encompasses all the water present on Earth is the hydrosphere. This includes not only the water found in oceans, rivers, and lakes, but also groundwater, glaciers, and water vapor in the atmosphere. The hydrosphere is a critical component of the Earth’s system, interacting with the atmosphere, lithosphere (the Earth's solid outer layer), and biosphere (the zone of life on Earth). Understanding the hydrosphere is essential for water resource management, climate studies, and ecological balance.

The other terms, while related to Earth's systems, refer to different concepts. Hydrology is the study of water, its movement, distribution, and properties, but does not represent the entirety of water on Earth. The atmosphere refers to the layer of gases surrounding the planet, and the lithosphere pertains to the Earth's solid crust and the upper part of the mantle, which deals with rock and soil rather than all water. Thus, the hydrosphere is the most accurate term for describing the collective whole of Earth's water resources.