How to solve radiometric dating problems
the elements beyond bismuth (Bi) in the Periodic Table of the Elements display radioactivity.
There are natually occurring radioactive isotopes of many of the other elements as well.
Studies of strata, the layering of rocks and earth, gave naturalists an appreciation that Earth may have been through many changes during its existence.
These layers often contained fossilized remains of unknown creatures, leading some to interpret a progression of organisms from layer to layer.
A short half-life, such as a few hours, means that the radiation is reduced to harmless levels quickly.
A longer half-life, such as hundreds or thousands of years, means that the radioisotope continues to emit harmful radiation for a very long period of time.
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.
Huxley, attacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions.Even more constraining were Kelvin's estimates of the age of the Sun, which were based on estimates of its thermal output and a theory that the Sun obtains its energy from gravitational collapse; Kelvin estimated that the Sun is about 20 million years old.Geologists such as Charles Lyell had trouble accepting such a short age for Earth.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.