of evolution was rejected by some. Darwin's contemporaries eventually came to accept the transmutation of species based upon fossil evidence, and the X Club (operative from 1864 to 1893) formed to defend the concept of evolution against opposition from the church and wealthy amateurs. At that time the specific evolutionary mechanism which Darwin provided - natural selection - was actively disputed by scientists in favour of alternative theories such as Lamarckism and orthogenesis. Darwin's gradualistic account was also opposed by the ideas of saltationism and catastrophism. Lord Kelvin led scientific opposition to gradualism on the basis of his thermodynamic calculations for the age of the Earth at between 24 and 400 million years, and his views favoured a version of theistic evolution accelerated by divine guidance. Geological estimates disputed Kelvin's age of the earth, and the geological approach gained strength in 1907 when radioactive dating of rocks revealed the Earth as billions of years old. The specific hereditary mechanism which Darwin hypothesized, pangenesis, which supported gradualism, also lacked any supporting evidence and was disputed by the empirical tests (1869 onwards) of Francis Galton. Although evolution itself was scientifically unchallenged, uncertainties about the mechanism in the era of "the eclipse of Darwinism" persisted from the 1880s until the 1930s' inclusion of Mendelian inheritance and the rise of the modern evolutionary synthesis. The modern synthesis rose to universal acceptance among biologists with the help of new evidence, such as that from genetics, which confirmed Darwin's predictions and refuted the competing hypotheses. Protestantism, especially in America, broke out in "acrid polemics" and argument about evolution from 1860 to the 1870s—with the turning point possibly marked by the death of Louis Agassiz in 1873—and by 1880 a form of "Christian evolution" was becoming the consensus. In Britain, while publication of The Descent of Man by Darwin in 1871 reinvigorated debate from the previous decade, Sir Henry Chadwick (1920-2008) notes a steady acceptance of evolution "among more educated Christians" between 1860 and 1885. As a result, evolutionary theory was "both permissible and respectable" by 1876. Frederick Temple's lectures on The Relations between Religion and Science (1884) on how evolution was not "antagonistic" to religion highlighted this trend. Temple's appointment as Archbishop of Canterbury in 1896 demonstrated the broad acceptance of evolution within the church hierarchy. For decades the Roman Catholic Church avoided officially rejecting evolution. However, the Church would rein in Catholics who proposed that