If we do not want to go into the intricacies of the term, then we can define environment as everything that surrounds us. Whatever we see around us is confined to the living component of the human eco-system. With time, the concept has undergone modifications. Today, environment means a single system of the interacting living and non-living natural components of the earth.
But the earth is not the only planet of the solar family, which again belongs to our home Galaxy — the Milky Way. There are about 100 billion such galaxies floating in the vast universe, each containing about 100 billion stars!! In this universe, not a single event can be said to be isolated, and no object is independent of the rest.
Since everything is interrelated with every other thing, logic demands-that the entire universe is our environment. But, for practical reasons, environmental study deals only with the system of interaction between non-living and living components of the globe.