The process of solar nuclear fusion was not yet known to science.
In 1895 John Perry challenged Kelvin's figure on the basis of his assumptions on conductivity, and Oliver Heaviside entered the dialogue, considering it "a vehicle to display the ability of his operator method to solve problems of astonishing complexity." Other scientists backed up Thomson's figures. Darwin, proposed that Earth and Moon had broken apart in their early days when they were both molten.
Because the time this accretion process took is not yet known, and predictions from different accretion models range from a few million up to about 100 million years, the difference between the age of Earth and of the oldest rocks is difficult to determine.
This led him to estimate that Earth was about 75,000 years old.
For biologists, even 100 million years seemed much too short to be plausible.
In Darwin's theory of evolution, the process of random heritable variation with cumulative selection requires great durations of time.
material and is consistent with the radiometric ages of the oldest-known terrestrial and lunar samples.
Following the development of radiometric age-dating in the early 20th century, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old.
Huxley, attacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions.