The earth is a vast, complex system powered by two sources of energy: an internal source (the decay of radioactive elements in the geosphere, which generates geothermal heat) and an external source (the solar radiation received from the Sun); the vast majority of the energy in the earth system comes from the Sun.
Everything in Earth's system can be placed into one of four major subsystems: land, water, living things, or air. These four subsystems are called "spheres." Specifically, they are the "lithosphere" (land), "hydrosphere" (water), "biosphere" (living things), and "atmosphere" (air).
Microscopical observations show the presence of simple in structure, abundant, and pervasive microorganisms. Researchers at the time came to the conclusion that there was a life force in the air.
A pair of nephridia is present on each segment of the earthworm, They are similar to flame cells in that they have tubules with cilia and function like a kidney to remove wastes.
