The planet that we live on; terrestrial globe. It is the fifth largest planet of the solar system and the third in distance from the sun diameter, c.12,760 km; period of revolution, one earth year; period of rotation, 24 hours.

Any of the metallic oxides formerly classed as elements, which are reduced with difficulty to an alkaline earth metal, rare earth metal, or certain other metals.

The composition of the crust is oxygen 47%, silicon 28%, aluminum 8%, iron 4.5%, calcium 3.5%, sodium and potassium 2.5% each and magnesium 2.2%. Hydrogen, carbon phosphorus, and sulphur are all present to an extent of less than 1%.