Due to the presence of water covering a major portion of its surface
Explanation
The Earth is unique in the solar system due to the abundance of liquid water on its surface. This physical characteristic is the primary determinant of its color when viewed from outer space, earning it the title "The Blue Planet."
Option Analysis:
- Because of the reflection of the blue sky is Incorrect: The "blue sky" is a phenomenon experienced from the Earth's surface looking up, caused by atmospheric scattering. While related to light physics, the reflection of the sky is not the reason the planet itself looks blue from the outside.
- Due to the presence of water covering a major portion of its surface is Correct: Approximately 71% (or two-thirds) of the Earth's surface is covered by water. Water molecules absorb longer wavelengths of light (such as red and yellow) and scatter or reflect shorter wavelengths (blue). Because water dominates the surface area, the overall appearance of the planet from space is blue.
- Because of the scattering of light by the atmosphere is Incorrect: The scattering of light by the atmosphere (Rayleigh scattering) is primarily responsible for the color of the sky as seen from the ground and the thin blue "halo" around the Earth's horizon. However, the solid blue color of the planetary disk is attributed to the vast oceans, not solely the atmosphere.
- Because it is composed primarily of blue rocks is Incorrect: The Earth's crust is composed of various minerals and rocks (silicates, basalts, granites) which appear brown, green, or grey, not blue.
Key Takeaway:
The Earth appears blue from outer space primarily because the majority of its surface is covered by water, which reflects blue wavelengths of sunlight.