In truth, both the human body and the planet Earth contain a number of interconnected systems that enable life to exist. The respiratory, digestive, reproductive, musculoskeletal, neurological, and immunological systems are all vital to human survival. The stability of the planet is dependent on the balance of its air, water, land, and life systems. Without all these components there can be no life as we know it. The human body is similar to the earth in many ways. Both have an atmosphere, water, land, and living organisms. The human body is also similar to the earth in that it relies on a balance of energy to function properly. If the amount of energy received by the body is not equal to the amount used by the body, then damage may occur. For example, if the amount of sunlight received by the earth is too much or too little, then excessive heat or cold could cause serious injury or death. The human body is also similar to the earth in that it needs oxygen to live. Oxygen is a gas that makes up half of the earth's atmosphere. Without it, none of us would be able to survive more than a few minutes. The human body requires fresh oxygen every minute to stay alive. This fact explains why most accidents happen on the road: people are trying to get from A to B as quickly as possible by going as fast as they can around other cars and objects.