Sunlight gives energy to the surface of earth, in other words, it warms the earth. Some is blocked by clouds and some is reflected away by large white masses of ice cap and glaciers.

Sunlight comes as light and heat, but not all of it reaches the earth. Ultra-violet light C, very dangerous to humans, is completely blocked by the ozone layer. Ultra-violet B, which causes sunburn and skin cancer is mostly blocked by the ozone layer. Most ultra-violet A light reaches the earth, where it does little damage.