Layer in the atmosphere found from the surface to a height of between 8 to 16 kilometers of altitude (average height 11 kilometers). The troposphere is thinnest at poles and gradually increases in thickness as one approaches the equator. This atmospheric layer contains about 80% of the total mass of the atmosphere. It is also the layer where the majority of our planet’s weather occurs. Maximum air temperature occurs near the Earth’s surface in this layer. With increasing altitude air temperature drops uniformly with increasing height at an average rate of 6.5° Celsius per 1000 meters (commonly called the Environmental Lapse Rate), until an average temperature of -56.5° Celsius is reached at the top of the troposphere.