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- Our body has plenty of water! Earth is almost entirely covered by water.
- But, how was all this water formed?
Let's take a closer look. - I'm the Oxygen and I have 8 electrons:
two in the first level and six in my upper level. - We are the Hydrogen and we have only one electron.
Atoms that have an incomplete upper level are not stable.
- I would like to have 8 electrons in my upper level!
- Hey! If you guys stick together, everything is gonna be fine.
This way of sharing electrons is called "chemical bond".
The molecule of water has two atoms of Hydrogen and one of Oxygen.
This bond makes the molecule be stable for billions of years.
- Cool! So the water can be much older than Earth?
- Sure! We have met in the sideral space!
- We were in the same material that formed the solar system.
The space among the stars, called Interstellar Medium, contains unbound atoms.
Eventually the atoms bound among each other to form the molecules.
However, the ultraviolet radiation from stars may destroy the molecules.
- Then how can the molecules escape from the stellar radiation?
The Interstellar Medium contains molecular clouds with plenty of gas and dust.
Dust grains can protect the molecules... - We can be hidden by grains!
- ... that are in the dark, impeaching the access of ultraviolet rays.
- How could the water coming from the interstellar medium arrive here on Earth?
Our Solar system was formed inside a molecular cloud.
- I got it! When the Earth was formed, the water came here inside dust grains!
- Oh no! - The primeval Earth was too warm.
Near the Sun only the rocky planets were formed, composed by refractory materials that are resistant to high temperatures.
- Seriously? And how about all this water we have here? Where did it come from?
From the agglutination of grains covered with ice...
... the primeval water was retained in objects that were formed away from the Sun.
Among them, the asteroids and comets that are orbiting the Sun.
- That's true! Comets and asteroids fell on Earth bringing water!
When heat was lost by Earth, water remained here forming the oceans.
The same water that came from space was used by dinosaurs, for instance...
... and also by all the living beings on Earth.
- Awesome! So the water that we drink... ... came from space!