World Water Day: How the Color of the Water Determined Everything That Sees Our Eyes

– Look, Mama! I can pour through the water.

about 3 hours ago

– Hey, that’s just because the water is almost transparent.

– Y, ¿Por qué no puedo ver si miro a través de un vase de leche?

– Because the water is so special that thousands of millions of years ago we lived right there…

Surely you have asked yourself at some time, like this fictional child, why some objects have some colors and others have others. Why are some almost transparent like water?

The answer to this question has to do with the human eye, with the water and, above all, with something as fascinating as our ancestors from thousands of years ago.

Perhaps there is a simple explanation for this fictitious child to understand, but BBC Mundo works with Spanish physicist Alberto Aparici to decipher it.

visible light

Our journey in search of an answer begins with something as basic as understanding what light consists of, that which allows us to see our surroundings.

Light, or visible light, is the part of electromagnetic radiation that is transmitted in the form of waves and that can be perceived by the human eye.

Because within electromagnetic waves there is a whole spectrum or classification according to the call wavelengthes decir, the distance between the peaks of the waves.

This is how, from longer to shorter wavelengths, we divide the electromagnetic spectrum into radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.

“The more strenght in the wave length, the more energy this wave contains and from there it can produce more important physical effects. They can do more damage if it is a living being or burn more if it is a material”, explains Aparici.

This is why, for example, while radio waves or microwaves are practically harmless to humans, X-rays or gamma rays can be harmful.

It is clear that we can get to see other ranks through, for example, equipment such as X-rays, but in what concerns the human eye, the visible range is our only refuge.

However, as Alberto Aparici clarifies, “there is no physical border between a range and another. I believe that the frontier is defined by our eyes, by what we can see”.

Within the tiny range that our eyes are able to see, humans have defined a spectrum of colors that resembles what we understand by the rainbow.

It was Isaac Newton who gave the first explanation about the visible spectrum and who dared to divide it into seven colors: red, orange, yellow, green, blue, blue and violet.

It is not surprising, therefore, that, in the electromagnetic spectrum, on both sides of the visible light, two ranges are found with references to the colors, the infrared and the ultraviolet.

The reflected colors

Arriving at this point safely thinking, if the objects receive the same visible light, why do we see one of a color and another of another color?

“When an object receives light, it absorbs some colors and bounces or reflects others. This has to do with the internal structure of the atoms that make up the object. Y the color you see is defined by the colors that do not absorb”, describe Aparici.

For example, if we have a blue book it is because, due to its composition, it absorbs all the red and green tones, but it rebounds the blue or violet ones.

If we see a yellow-colored plane tree, it means that its structure absorbs the blue color and reflects the green and red, which sums up what we see in the yellow color.

Once explained the reason for the colors we see, remove the bather because it touches the water.

¿Transparent or blue?

If we observe a water vase and it has no impurities, we can assure you that it is colorless or transparent. But if we echamos un vistazo al mar, there the thing changes. The majority will coincide in that it has a blue tone, or even sometimes green.

The explanation of its transparency is that “the water, being liquid, let the light pass through. In solid objects, the ones we are used to, there are all kinds of internal surfaces with which the light is found and ends up bouncing -and generating color in our view-. In the water, the light enters, it is not absorbed but neither is it rebounded. The light simply passes through the water”, explains Aparici.

However, when water is present in large quantities, other factors come into play.

Basándonos in the sea, at a cable of 7 or 8 meters, the water is able to absorb the red color, while the blue reaches a deeper depth without being absorbed or rebotado by the water. The reason why we see the blue sea is because of the impurities that there are that are capable of rebounding the only color that falls, which is the blue.

If you have a large mass of water completely still and without impurities, we would see the bottom. Except that it was so big that it could also absorb the blue color, which would cause us to see it black.

See under the water

The transparency of the water may seem taken for granted, but if we find a view of the electromagnetic spectrum, we will realize that this only occurs in visible light.

In the ultraviolet and infrared ranges, the water is not transparent at all, since it absorbs the colors very easily.

And it is precisely this particularity that explains the fascinating nature of our evolution. When more than 3,000 million years ago we were only unicellular bacteria and lived under water, the light started to become an essential element.

“Because a great part of our ancestors, the bien lived thanks to the light, because they were photosynthetic, like the plants today, the bien moved in surroundings in which someone would go to eat if they saw them. Those beings were interested in knowing where there was light and where there was no light. Those who were photosynthetic wanted to go to the light and those who wanted to escape from predators wanted to go to the dark to hide”, says Alberto.

These bacteria developed a type of organ or sensor to detect where the light came from. In what range of the spectrum could these sensors work? In the only one where the water was almost transparent and the light reached them, it was decir, in the range of visible light.

It was that need to be able to move through the water that led our unicellular ancestors to develop those proto-eyes. But these light sensors evolved in such a way that, it is estimated that at least 550 million years ago the first versions of an animal eye existed.

Therefore, that today you see a red tomato or a green plant is thanks to which your unicellular ancestors bet on their survival to that small yield in which the water is almost transparent. (I)