Has the Earth always been blue?

The blue planet... Everyone knows this nickname attributed to our Earth. However, over the ages, our planet has not always sported the same colors. From blue to white, it has gone through orange and now offers a beautiful mix of shades.

[IN VIDEO] What color is the Sun? If the Sun is yellow, it's because the sky is blue... That's what this video explains, which reminds us that the peak of sunlight is located more in the green. Strange but explainable.

When it was formed, about 4.6 billion years ago, the Earth was made up entirely of rocks. Its appearance must then, more or less, recall that of Mercury. But soon, a meteor shower falls on our planet. Meteorites that bring it water, at least that's what researchers think. Thus, a few hundred million years after its formation, the Earth is covered with oceans. And, as we all know, the sea is blue. Our planet is then adorned with this color.

It wasn't until later, around 3.2 billion years ago, that continents -- as we know them today -- appear. Rock surfaces that reflect some of the energy our planet receives from the Sun. The Earth is cooling and some regions are experiencing glaciation. And here is our blue planet which sports a few orange spots here, and white there.

It is around 2.9 billion years old, and the massive presence of aerosols – formed by interactions between methane and sunlight – in the Earth's atmosphere gives it an orange color. A color reminiscent of that of Titan, one of Saturn's satellites.

The atmosphere of Titan, one of the satellites of Saturn, contains, as was the case for that of the Earth, aerosols which give it an orange color. © NASA, Wikipedia, Public domain

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After blue, ocher and orange, white and green

A little later still, 2.45 to 2.2 billion years ago, what specialists call the Great Oxidation Event (GEO) occurs. A few water molecules reach the stratosphere and are broken up by the Sun's ultraviolet radiation. Oxygen then falls to the ground and a phase of oxidation of the earth's crust -- which will last hundreds of millions of years -- begins. Oxygen seeps into the oceans and gradually invades the atmosphere. The quantity of methane is decreasing, accompanied by a drop in temperatures which leads to the first glaciation 2.4 billion years ago.

Between 717 and 660 million years ago, then around 645 and 635 million years ago, the Earth once again transformed into a veritable ball of ice. This time, probably because of the breakup of the supercontinent Rodinia. This would indeed have caused a considerable increase in silicate erosion and thus a sharp drop in CO ₂ .

It is only between 419 and 358 million years ago that the continents will welcome life and that the green color will extend over previously rather brown or ocher surfaces. Leaving an Earth with the colors that we know today: blue for the most part, for the oceans, but also green and brown on the side of the continents, and finally white at the poles.

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