Қоғамдық салқындану теориясы: Ескірген геофизикалық көзқарас

the obsolete theory of global cooling
Before the concept of plate tectonics, global cooling was 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. 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.

The Earth was compared to a cooling ball of iron, or a steam boiler with shifting boiler plates. By the early 1900s, it was known that temperature increased with increasing depth. With the thickness of the crust, the "boiler plates", being estimated at ten to fifty miles, the downward pressure would be hundreds of thousands of pounds per square inch. Although groundwater was expected to turn to steam at a great depth, usually the downward pressure would contain any steam. Steam's effect upon molten rock was suspected of being a cause of volcanoes and earthquakes, as it had been noticed that most volcanoes are near water. It was not clear whether the molten rock from volcanoes had its origin in the molten rock under the crust, or if increased heat due to pressure under mountains caused the rock to melt. One of the reasons for volcanoes was as a way in which "the contracting earth disposes of the matter it can no longer contain." A relationship between earthquakes and volcanoes had been noted, although the causes were not known. Fault lines and earthquakes tended to happen along the boundaries of the shifting "boiler plates", but the folding of mountains indicated that sometimes the plates buckled. Similarly, Professor Robert T. Hill explained at that time that "the rocks are being folded, fractured and otherwise broken or deformed by the great shrinking and settling of the earth's crust as a whole. The contraction of the earth's sphere is the physical shrinkage of age that is measured in aeons instead of years. The prehistoric convulsions of the earth before man inhabited this planet were terrific, almost inconceivable." There "was no doubt that earthquakes are diminishing." The displacement of the 1906 San Francisco earthquake was only a few feet, while prehistoric earthquakes made fissures and slides of 20,000 feet.

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. After resumption of Lunar exploration in the 1990s, it was discovered there are scarps across the Moon's surface which are caused by contraction due to cooling.