The impeller made out of cast material in many cases may be called rotor, also. It is cheaper to cast the radial impeller right in the support it is fitted on, which is put in motion by the gearbox from an electric motor, combustion engine or by steam driven turbine.
Earth remains the only known planet to host life, due to a unique combination of factors. However, continued monitoring of alien worlds might one day change that, by finding other planets that share these attributes or by discovering other ways that life has found to blossom in the universe.
Earth, our life supporting planet. Earth, the third closest planet to the Sun, is also the only known planet that supports life. The atmosphere contains 78% nitrogen, 21% oxygen, and 1% argon. The atmospheric layers are  in order of distance from sea level  the troposphere (10 km), stratosphere (45 km), mesosphere (80 km), thermosphere (200 km), and exosphere (400 km).