Stages of development and general laws of the geographic envelope
The envelope developed in three stages. In the pre-biogenic stage (from about 4.6 billion years ago to 570 million years ago) the lithosphere, atmosphere and hydrosphere formed; life existed even then, but it consisted of very simple organisms and did not noticeably affect the envelope. In the biogenic stage organisms developed and the biosphere formed (in modern geochronology the Paleozoic began 541 million years ago, the Mesozoic 252 million and the Cenozoic 66 million years ago). The anthropogenic stage began with the appearance of humans (the textbook says 2 million years; modern Homo sapiens appeared about 300 000 years ago), and today economic activity has caused environmental problems such as the Aral Sea crisis. The laws are: wholeness (if one component changes, the others change too), cycling of matter and energy, rhythmicity (daily, from the Earth’s rotation on its axis; annual, from its revolution around the Sun), and zonation and altitudinal belts. Zonation is caused by the sphericity of the Earth, because sunlight decreases from the equator toward the poles.
“Time line”: draw a 4.6-billion-year line on the wall (1 billion years = 20 cm) and students stick on the pre-biogenic, biogenic and anthropogenic stages, the dinosaurs and the appearance of humans.