Hydrosphere: definition for children

On Earth, water is one of the most important elements for life, being vital for humans and all living beings. The hydrosphere is the set of liquid parts of the planet, both seas and oceans such as lakes, rivers, glaciers or groundwater.

Next, in this lesson from unPROFESOR.com we are going to offer you a definition of hydrosphere for kids and that, thus, they can better understand this concept. We will also know the evolution of water throughout the earth's crust.

Water circulates throughout the planet, transforming its physical state into a series of cyclical processes that we call hydrological cycle. We call this layer of liquid element that surrounds the Earth hydrosphere and it has its origin in the condensation and solidification of the existing water vapor in the earth's primitive atmosphere.

Through water and its changes within the hydrological cycle there is a constant transformation of the planetary surface, shaping the relief, being also responsible for the climate regulation.

In this other lesson we discover you How is rain formed with a simple explanation and suitable for all ages.

The water covers almost three quarters of the Earth's surface and its distribution is as follows:

• The 97% of water in the hydrological cycle is located in seas, oceans and lakes saline.
• The 3% of the planet's water It is sweet, with the following distribution: 75% of glaciers and ice sheets, 24% of groundwater and less than 0.5% corresponds to rivers, lakes, the soil and the atmosphere (which is in the form of water vapor and accounts for a minimal part of the total -0,001%-).
• We cannot forget the one of the biosphere found in the body of living beings, assuming a 0,0005%.

At the time of the ice ages, the percentage of water in glaciers and ice sheets was higher, and lower in the oceans.

The density of ocean water is greater than fresh water due to its salinity, since the greater the quantity of salts, the more density. The reverse occurs with temperature, the higher the temperature, the less density. Therefore, the densest water is found in the polar seas.

Changes in the state of water and the hydrological cycle take place thanks to the energy from the sun (causes evaporation and evapotranspiration) and the force of gravity (produces precipitation, runoff and infiltration), giving rise to a closed circuit that sets in motion large masses of energy and water in the hydrosphere.

The energy of the Sun is responsible for the production of the water evaporation of the surface of the planet, both of the seas and oceans and of the continents, taking place an accumulation of much energy as latent heat. In addition, we must not forget the water vapor that living beings perspire. The two processes are called evapotranspiration.

Following the cycle, when ascending there is a cooling and condensation from the water, forming clouds. Through the rainfall, the water returns to the continents and oceans in the form of rain or snow, giving rise to several processes:

• Surface runoff: in soils saturated with water there is retention and the liquid passes over the surface with various currents, forming rivers, streams, etc.
• Underground runoff: soils that are permeable and do not saturate produce infiltration on the ground, forming groundwater and aquifers that eventually flow into the sea.
• Withholdings: there are also water retentions that form lakes, swamps, glaciers, etc.

Regarding the balance of the hydrological cycle, in the oceans there is greater evaporation of water than it precipitates. On the other hand, more water precipitates on the continents than it evaporates. The continents have a positive balance of water and the oceans, negative. This is offset by the water that returns to the oceans from the continents, balancing the global balance of the hydrological cycle.