Geophysical global cooling

This article is about the obsolete theory of global cooling. For the theory positing an overall cooling of the Earth and perhaps the commencement of glaciation or even an ice age, see Global cooling.

Before the concept of plate tectonics, global cooling was a reference to a geophysical theory by James Dwight Dana, also referred to as the "contracting earth" theory. It suggested that the Earth had been in a molten state, and features such as mountains formed as it cooled and shrank.^[1] As the interior of the Earth cooled and shrank, the rigid crust would have to shrink and crumple. The crumpling could produce features such as mountain ranges.

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Some of the objections include:

• A shrinking planet would increase its speed of rotation. There is no evidence of such an increase.
• There was no overall pattern to mountain ranges. When this theory was rejected, the patterns did not fit what was expected if continents never moved, nor the known evidence of drifting continents (the plate movement causing continental drift had not been identified at the time). Plate tectonics now explains many mountain range patterns.
• Some large scale features of the Earth are tensional rather than compressive.
• After radioactive decay was discovered, it was realized it would release heat inside the planet. This undermines the cooling effect upon which the shrinking planet theory is based.^[2]

This theory is now disproven and considered obsolete. In contrast to Earth, however, global cooling remains the dominant explanation for scarp (cliff) features on the planet Mercury.

References

1. ^ http://www.bbm.me.uk/portsdown/PH_061_History_a.htm
2. ^ Wilcoxson, Kent H. (1967). Chains of Fire, 1, Philadelphia: Chilton Company, 140-141.