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There are lots of physical factors that may affect the current condition of our environment. These factors may include water, light and atmosphere. First and foremost is water. As we all know, water is the basic ingredient of life. It makes up three-fourths or seventy five percent of the earth. It is also the habitat of most organisms. Another factor is the light. Light is a limiting factor to terrestrial organisms. It is needed by green plants for photosynthesis. In large bodies of water like the oceans, plants are limited by the depth to which sunlight can penetrate. In the clear lakes, green plants survive only in first thirty meters or so. However when waters become turbid, sufficient light may reach only about a meter beneath the surface.
Light conditions vary from place to place in the same ways as organisms vary in places with bright or dim supply of light. Deep valleys, forest floors and the sides of the hill are places where organisms with low requirement can stay. Some examples of plants here are ferns and mosses, while examples of animals may be the snails, toads, salamanders and snakes. Some animals are capable of living in total darkness. Blind fishes with empty sockets, where their evolutionary ancestors have eyes, survive in the darkness of the ocean floor in underground streams and rivers. Other organisms like bacteria, live without light. They simply survive by the food and energy they store.
Last factor is the atmosphere. The air surrounding us has an important effect on living things except the anaerobic bacteria. Anaerobic bacteria are a species of bacteria that can survive without the presence of air. Land dwellers obtain oxygen directly from the atmosphere. Water dwellers obtain their supply from the oxygen dissolved in water where they live. However, deep ocean life does not receive the same supply of oxygen as the other aquatic forms of life. Since water receives its supply of oxygen from air, the oxygen content of water decreases as water goes deeper.
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