The earth grew by a process called collisional accretion. This is a process whereby big rocks collide in space and the collisions build up the planet... this all happened about 4,500,000,000 years ago!!!

The build blocks had in them about 5 wt % water; the residual water left over is where the oceans came from.

Note from ScienceLine: Wt/wt % is a way to express the concentration of an aqueous solution, wt/wt% typically means the number of grams of solute in 100 grams of solution.