Question

the earth looks blue from space why?

Answer 1

It's due to scattering of light since our earth contains almost 70% of water, when sunlight goes through our earths atmosphere, the water starts absorbing the red light in this way water also enhances the scattering of blue light in its environment. 

Answer 2

Because 2/3 rd of the earth is covered by water so it is often called blue green planet