Boundaries and properties of the geographic envelope
The geographic envelope is the single unit of four interacting parts: the lower layer of the atmosphere (troposphere), the upper porous layer of the lithosphere, the whole hydrosphere and the biosphere. Scientists often put its thickness at 30–35 km; according to the textbook its upper boundary runs near the ozone layer and its lower boundary at the base of the porous rocks (different scientists draw the boundary differently). The ozone layer protects living things on Earth from the Sun’s ultraviolet rays. The envelope has three main properties: its parts constantly act on one another; matter and energy are exchanged; and life, including human society, exists in it. Most processes run on solar energy and fewer on the Earth’s internal energy. Exchange speeds differ: ocean water is renewed about once in 3 000 years, while moisture in the atmosphere is renewed in only 10 days. The vertical structure is the placement of the parts along height, and the horizontal structure is seen in the succession of climate zones and natural zones along latitude.
“Chain of four parts”: four groups represent the atmosphere, lithosphere, hydrosphere and biosphere. They take turns telling a water drop’s journey, showing how it passes through each part.