Seawater is a fascinating substance with a multitude of properties that make it vital for life on Earth. It is the water that makes up the world's oceans and seas, and it covers more than 70% of the Earth's surface.

Seawater is a complex mixture of water, salt, minerals, and other substances that are essential for life.

One of the most interesting things about seawater is that it is a veritable liquid mineral. It contains an average of 35.7 million tons of minerals per cubic kilometer of seawater, which is significantly more than the amount of minerals found in freshwater sources.

In fact, 80% of the world's more than 100 known elements can be found in seawater. These minerals are essential for the health and growth of many marine organisms, and they also have important industrial and economic uses.

Seawater is also a source of fresh water on land and a regulator of climate. Every year, 4.5 million cubic kilometers of fresh water evaporates from the world's oceans, and 90% of it returns to the ocean through rainfall.

The remaining 10% turns into rain and snow falling on the earth, and then returns to the ocean along rivers. This process of evaporation and precipitation is a critical component of the Earth's water cycle, which helps to regulate the planet's climate.

However, despite the abundance of seawater, access to fresh water is a major challenge in many parts of the world. This is where desalination technology comes in. Desalination is the process of removing salt and other minerals from seawater, making it safe and usable for human consumption.

As the ecological environment deteriorates, the last way for humans to solve the water shortage is likely to be the desalination of seawater. The technology for desalination is developing into an industry, and it has the potential to provide a sustainable source of fresh water for communities around the world.

The blue color of seawater is another fascinating aspect of this substance. The nature of sunlight is electromagnetic waves, and visible light is made up of seven colors: red, orange, yellow, green, blue, indigo, and violet.

When sunlight shines on seawater, red light has a longer wavelength and less penetrating ability, and is most easily absorbed by seawater and sea creatures. Blue or purple light is not easily absorbed by seawater and sunlight, and has a stronger penetrating ability.

At the same time, blue light is also easy to be reflected back by the seawater or sea creatures. Seawater reflects blue light and absorbs other colors of light, which is why seawater appears blue in the human eye. However, this is only true for water at a certain depth.

If the water is not deep enough, it will not be able to absorb the other colors of light. In shallower waters or waves, the blue color may not be as visible. The penetration of light is also limited, and light can only penetrate up to around 200 meters, beyond which there will not be any bright light.

The University of California, Santa Barbara (UCSB) has a page on ocean color science that explains that the ocean appears blue because of its absorption spectrum, rather than (Rayleigh) scattering.

In the visible region, the long-wavelength region (red and orange light) is absorbed the most, followed by the medium wavelengths of yellow and green light. The short wavelengths of blue and violet light are absorbed the least. This also explains why very pure water that does not contain any particles will exhibit a dark blue color.