Dating on earth summary
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.
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.
It is used in dating things such as bone, cloth, wood and plant fibers that were created in the relatively recent past by human activities.
By measuring the concentration of the stable end product of the decay, coupled with knowledge of the half life and initial concentration of the decaying element, the age of the rock can be calculated.
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.
You probably have seen or read news stories about fascinating ancient artifacts.
At an archaeological dig, a piece of wooden tool is unearthed and the archaeologist finds it to be 5,000 years old.