Probability Definition. The probability of an event is a number between $0$ to $1$ which measures the chance of that event occurring. The likelihood of the occurrence of the event increases as the probability varies from $0$ to $1$. The probability of the occurrence of an impossible event is $0$ and that of a certain to occur event is $1$.
As altitude increases, air pressure decreases. Gravity causes the atmosphere to become heavier the closer you are to the ground. The atmosphere may seem weightless but all the â¦ air molecules add up to a tremendous amount of mass.
In general, temperature increases with depth below the earth's surface. The rate of temperature increase is called the geothermal gradient. The geothermal gradient varies depending on the geology beneath the surface. The following map shows how the geothermal gradients vary within the United States: