- Gagarin, Yuri A. (1934-1968)
- Gaia Hypothesis
- Galilei, Galileo (1564-1642)
- Gell-Mann, Murray (1929- )
- Gemstones
- Geochemistry
- Geographic and Magnetic Poles
- Geologic Map
- Geologic Time
- Geology
- Geothermal Deep-ocean Vents
- Geothermal Energy
- Geothermal Gradient
- Gesner, Konrad von (1516-1565)
- Geyser
- GIS
- Glacial Landforms
- Glaciation
- Glaciers
- Glass
- Glenn Jr., John H. (1921- )
- Global Warming
- Gneiss
- Goddard, Robert H. (1882-1945)
- Goldschmidt, Victor (1888-1947)
- GPS (Global Positioning System)
- Granite
- Graphite
- Gravitational Constant
- Gravity and the Gravitational Field
