Why does Earth look blue when seen from space?

Earth appears blue when viewed from space primarily due to the presence of its vast oceans and its atmosphere.

The blue appearance of the oceans is a result of how water interacts with sunlight. While water is transparent, it absorbs longer wavelengths of light (such as red and yellow) more readily than shorter wavelengths. Blue-green light penetrates deeper and is scattered by water molecules and suspended particles, reflecting back to the observer's eye.1

Simultaneously, the atmosphere contributes to the planet's blue hue through a phenomenon known as Rayleigh scattering. As sunlight enters the atmosphere, gas molecules and small particles scatter shorter, blue wavelengths of light more intensely than longer wavelengths. This scattered light is what gives the sky its blue color when viewed from the surface and contributes to the blue appearance of the planet from space. Together, these optical processes involving the hydrosphere and the atmosphere create the characteristic blue marble effect seen from orbit.2341