Earth's four spheres are the atmosphere, biosphere, hydrosphere, and lithosphere - air, life, water, and rock, respectively. At first glance, it seems that an isolated event may affect one or two spheres, but not all of them. The truth is that all the spheres are connected with one another. An easy example is a forest fire. The fire itself destroys plants and trees (biosphere), and pollutes the air (atmosphere). The air pollutants may cause harm to birds or other life (biosphere) in the atmosphere. The lack of trees and plants increases the possibility of erosion (lithosphere), and erosion can cause pollution, or murkiness in the water (hydrosphere). This ultimately causes increased harm and hardship to the animals (biosphere), depending on the water and the shelter of the forest.