earth, in geology and astronomy: The Geologic Earth

Knowledge of the earth's interior has been gathered by three methods: by the analysis of earthquake waves passing through the earth (see seismology), by analogy with the composition of meteorites, and by consideration of the earth's size, shape, and density. Research by these methods indicates that the earth has a zoned interior, consisting of concentric shells differing from one another by size, chemical makeup, and density. The earth is undoubtedly much denser near the center than it is at the surface, because the average density of rocks near the surface is c.2.8 g/cc, while the average density of the entire earth is c.5.5 g/cc.

Sections in this article:

• Introduction
• The Origin of the Earth
• The Change in Seasons
• Rotation and Revolution
• The Astronomical Earth
• The Earth's Core
• The Earth's Mantle
• The Earth's Crust and the Moho
• The Geologic Earth
• Bibliography

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