The ocean covers 71% of the Earth’s surface. If seawater were spread evenly across the land, it would create a hydrosphere layer approximately 2,700 meters thick.
However, around 4-5 billion years ago, when the Earth was newly formed, its surface had no water and no life. As the Earth gradually cooled, water vapor in the atmosphere condensed into liquid water, which then fell as rain, accumulating in depressions over time and eventually forming primordial lakes and oceans. The first living organisms emerged in these oceans, which were primordial lakes.
The Earth’s hydrosphere exists between the atmosphere and the geosphere. It includes oceans, lakes, rivers, wetlands, groundwater, and streams (in liquid form) as well as glaciers (in solid form). According to scientific estimates, the total volume of water on Earth’s surface is about 1.4 billion cubic kilometers, with oceans accounting for 97.3% and glaciers on land comprising 2.7%. The amount of water in the atmosphere compared to these two types is negligible.
The Cyclic Movement of the Hydrosphere (Image: cmmacs)
Under the sunlight, the Earth’s hydrosphere is in constant cyclical motion. Water on the surface evaporates into vapor in the atmosphere, and under suitable conditions, this vapor condenses into rain that falls back to the Earth and oceans. Surface water gathers into streams, rivers, and lakes, flowing into oceans or seeping into the ground, where it becomes groundwater through cracks in the rock, or it may directly evaporate back into the atmosphere. In the water cycle, the atmosphere serves as the primary transport medium for water. Thanks to this large-scale, continuous water cycle, the Earth’s surface is constantly changing, and life flourishes.
