The rocks that gave birth to Earth already contained water, according to our partner The Conversation.
When the Earth's surface began to cool down forming a solid crust, the atmosphere filled with water vapor.
And it was this vapor that formed ever larger bodies of water.
The analysis of this phenomenon was carried out by Guillaume Paris, geochemist and CNRS researcher at the Nancy Petrographic and Geochemical Research Center (University of Lorraine).
What is an ocean?
It is a large expanse of salt water between two continents.
To form oceans, you then need three ingredients: water on the seabed, continents, and a very large pinch of salt.
To understand the formation of the oceans, we will go back in time, very far, more than 4.5 billion years ago.
At that time, the Solar System was just a huge cloud of gas and dust which carried within it all the ingredients that will make it possible to form the Sun, the planets, and therefore the Earth and its oceans.
The core of this cloud is very hot and will become the sun.
The dust present in the cloud will revolve around the young Sun and gradually stick to one another, thus creating rocks, which will form small planets, then larger planets, but also comets or asteroids.
Asteroids (artist's view) © Gam-Ol / Pixabay
So where does the water come from in all of this?
For a long time, scientists thought that the Earth was built from waterless rocks formed too close to the Sun.
They therefore thought that the water had been brought to Earth, after its formation, by comets and asteroids.
These, formed further from the Sun, contained water in the form of ice.
However, this hypothesis was recently questioned by a researcher, Laurette Piani.
She showed that in fact, the rocks that gave birth to Earth already contained water!
To understand how the first oceans were formed, let's move forward a few million years.
At first, Earth is a very different planet from the one we know.
It is very hot on its surface.
There are still neither oceans nor continents: there is only molten rock, magma.
This will cool down forming a solid crust and an atmosphere that contains water vapor.
Gradually, this water vapor falls back in the form of rain, first forming small lakes, then larger and larger bodies of water.
Atlantic coast photography © Luc Dobigeon / Unsplash
Over time, the surface of the Earth changes.
Its surface is organized into tectonic plates, these large groups that move in relation to each other, generating earthquakes or even mountain ranges.
The plates have relief, in particular because of the nature of the rocks which constitute them.
It is the structure of the plates on the surface of the Earth that explains why there are oceans and continents.
The thickest parts of tectonic plates are the continents, the thinner parts form at the level of ocean ridges (a kind of large submarine volcano chain).
When rainwater or rivers flow, they go up and down.
So water accumulates on the fine parts of the tectonic plates and ends up forming large areas there: the oceans.
There you go, the oceans are ready.
Our dossier "SOLAR SYSTEM"
Oh no, we forgot the salt!
Salt comes from the wear and tear of rocks on which rainwater flows.
Water removes chemical elements from these rocks, mineral salts, which are then transported by rivers and gradually accumulate in the oceans, giving it its special taste ...
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This analysis was written by Guillaume Paris, geochemist and CNRS researcher at the Nancy Petrographic and Geochemical Research Center (University of Lorraine).
The original article was published on The Conversation website.
Declaration of interests
Guillaume Paris does not work, does not advise, does not own shares, does not receive funds from an organization that could benefit from this article, and has not declared any affiliation other than his research organization.
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