Have you ever heard blue planet and didn’t know what it meant? The blue planet is another way of calling our planet, that is, Earth, as well as Mars is also known as the red planet. If we look at the photographs taken from space, we can get an idea of why the Earth is called a blue planet, however, why is it like that? What does that color bring to the Earth?
Why is Earth called a blue planet?
It is only necessary to look at a photograph of the Earth seen from space to understand why our planet is known as the blue planet, because it mainly stands out as a large blue sphere . But why does it have this color? The blue tones of our planet are due to two basic factors: the water of the seas and oceans and our atmosphere . In this section we will talk about the first one, and in the next one about the atmosphere.
The hydrosphere is the water found on the surface of our planet, that is, the seas, oceans, rivers, poles, glaciers, swamps and lakes that cover the surface of the earth. During the life of the earth it has not always been this way, in fact, it was not until volcanic eruptions released a large amount of steam into the air that condensed and caused intense rains for thousands of years that the earth was not flooded For the water.
The fact is that, today, water occupies 360 million square kilometers of the earth’s surface while the earth only occupies 148. This means that on our planet there are more than 1,400 cubic kilometers of water . But, why is it blue? Why, when observed from space, or from the beach, do we see blue water while the one we drink is transparent?
There are many people who believe that sea water is blue because it reflects the blue of the sky, but that is not the case. Sea water is blue simply because water is blue . In a glass or a bottle we see it transparent, however, that is why a larger mass of water is needed to be able to observe it.
The reason is that when light passes through water, it absorbs a large part of this light, specifically, it absorbs the colors red, yellow and orange, while the colors green and blue manage to penetrate it. That is why when the water is shallow, like in a glass or when we are right on the shore, the water is transparent, while the deeper the amount of water, the more blue it will be.
The Earth has not always been blue, in fact, the Earth has changed a lot throughout its millions of years of existence. In the beginning, the Earth’s atmosphere had a composition very different from what it has today – the one that gives the color blue to the sky, from Earth, or to Earth, from space. The constant volcanic eruptions that occurred on our planet released a large amount of water vapor into the air, which when they fell, eventually formed the oceans and seas.
In those seas and oceans algae began to be born and grow. They consume carbon dioxide and make oxygen. If we take into account that at that time carbon dioxide was very abundant and that no animal consumed oxygen, the proliferation of algae meant that over the centuries they managed to transform the composition of the atmosphere until they reached something similar to what we have today.
The fact is that when we observe the sky during the day it is blue , the same happens when we look at the earth from space, whose atmosphere is revealed to us in a bluish tone. This has a lot to do with the composition of our atmosphere and with the theory of light.
The source that emits light towards our planet is the sun. This star emits different types of light, which combined we can receive as a white light. This light, which reaches our planet 8 minutes after leaving the sun, must first pass through the different layers of our atmosphere. As we have mentioned, there are different molecules that make up our atmosphere, but among all of them, the main one is nitrogen. One of the characteristics of nitrogen molecules is that when they receive light they re-emit it in another direction depending on their wavelength.
When light reaches the atmosphere, long-length lights (red, green, and yellow) hit the surface or are re-emitted into space, while short-length blue light is reflected and scattered.
Since when is Earth called the blue planet?
The reality is that the nickname of the blue planet is quite recent, something logical if we consider that it is not so long ago that we have been able to observe the appearance of the Earth from space. The reality is that this name made a fortune, became popular and survived to this day from the 60s and 70s .
At that time, the world was divided into two great political-economic blocs, the capitalist bloc headed by the US and the communist bloc commanded by the USSR. This historical epoch is known as the cold war, because although a direct conflict was not reached, these two countries did face each other in the rest of the possible areas. In these years, what was known as the space race arose , a race in which both States tried to be the first to make manned trips to space and to reach the moon.
The fact is that the Russian cosmonauts and the American astronauts who left our atmosphere and observed the Earth for the first time stressed that from “out there” our planet looks like a large blue sphere , it is the blue planet.