Water

demonstrate an understanding that the presence of liquid water is probably an essential requirement for life
describe the present theories about the origin of water on Earth
describe methods used by astronomers to determine the origin of water on Earth (for example analysis of water on a comet by the Rosetta probe)

More than 70% of the Earth's surface is covered in water. Water on Earth is vital to the life present now and it was vital to our own evolution as all life originated in the oceans.

Where did the water on Earth come from?

There is not a definite answer to this just several theories.

• Water may have been brought to Earth when comets or water rich meteorites collided with the prehistoric Earth.
• Gases from the numerous chemical reactions happening on the surface of the early Earth may have contained sufficient water to form the oceans. The collision of Theia, which resulted in the formation of the Moon, may have had a significant role in this process.
• Bacteria in the Earth's early oceans may have produced water using Hydrogen Sulphide and Carbon Dioxide.