Where Does Earth Get Its Water

We live on Earth, the so-called blue planet. Without water, Earth would not be "blue" at all, not to mention the life that is bred on the planet because of the existence of the universal solvent.

Although minerals at the Earth's crust contain ingredients for making water, the majority of water, which exist on the surface of the planet, is believed to be delivered from the space. Scientists contemplated two possible carriers that might have brought us water: asteroids and comets. 

There are millions of asteroids in a belt shape zone between Mars and Jupiter, with the size ranging from 1 to 1000 kilometer in diameter, no wonder some of them are considered minor planets, especially those of the inner Solar System. The composition of asteroids varies, but some of them have a lot of water. For example, Ceres the most massive object in the asteroid belt is covered by an icy mantle.

Comets, the second possible carrier of water, are small icy bodies that have highly eccentric orbits. When a comet gets close enough to the Sun, the irradiated heat from the Sun evaporates its water and gaseous molecules, producing a visible tail. Comets are made of loosely packed ice, dust, and small rocky particles. 

Through isotopic analysis of the hydrogens, scientists have concluded that asteroids are likely the primary source of Earth's water because their deuterium to hydrogen ratio match better.

Source: It's Okay to Be Smart via Youtube