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In the mid-18th century, the naturalist Mikhail Lomonosov suggested that Earth had been created separately from, and several hundred thousand years before, the rest of the universe. In 1779 the Comte du Buffon tried to obtain a value for the age of Earth using an experiment: He created a small globe that resembled Earth in composition and then measured its rate of cooling.
This led him to estimate that Earth was about 75,000 years old.
giving a lower limit for the age of the solar system.
It is hypothesised that the accretion of Earth began soon after the formation of the calcium-aluminium-rich inclusions and the meteorites.
Thus the age of the oldest terrestrial rock gives a minimum for the age of Earth, assuming that no rock has been intact for longer than the Earth itself.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.He calculated the amount of time it would have taken for tidal friction to give Earth its current 24-hour day.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.However, they assumed that the Sun was only glowing from the heat of its gravitational contraction.The process of solar nuclear fusion was not yet known to science.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.The physicist Hermann von Helmholtz (in 1856) and astronomer Simon Newcomb (in 1892) contributed their own calculations of 22 and 18 million years respectively to the debate: they independently calculated the amount of time it would take for the Sun to condense down to its current diameter and brightness from the nebula of gas and dust from which it was born.Their values were consistent with Thomson's calculations.