Crust (geology) depth, reaching values typically in the range from about to at the boundary with the underlying mantle. The temperature increases by as much as for every kilometer locally in the upper part of the crust, but the geothermal gradient is smaller in deeper crust. The continental crust has an average composition similar to that of andesite. The most abundant minerals in Earth's continental crust are feldspars, which make up about 41% of the crust by weight, followed by quartz at 12%, and pyroxenes at 11%. Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much
Age of the Earth the Earth itself. In 1892, Thomson had been made Lord Kelvin in appreciation of his many scientific accomplishments. Kelvin calculated the age of the Earth by using thermal gradients, and he arrived at an estimate of about 100 million years. He did not realize that the Earth mantle was convecting, and this invalidated his estimate. In 1895, John Perry produced an age-of-Earth estimate of 2 to 3 billion years using a model of a convective mantle and thin crust. Kelvin stuck by his estimate of 100 million years, and later reduced it to about 20 million years. The discovery of