Radiometric dating timeline
Before then, the Bible had provided the only estimate for the age of the world: about 6,000 years, with Genesis as the history book.
Hutton's theories were short on evidence at first, but by 1830 most scientists concurred that Noah's ark was more allegory than reality as they documented geological layering.
Certain isotopes are unstable and undergo a process of radioactive decay, slowly and steadily transforming, molecule by molecule, into a different isotope.
This rate of decay is constant for a given isotope, and the time it takes for one-half of a particular isotope to decay is its radioactive half-life.
By dating rocks of known ages which give highly inflated ages, geologists have shown this method can’t give reliable absolute ages.
Many geologists claim that radiometric “clocks” show rocks to be millions of years old.
But for humans whose life span rarely reaches more than 100 years, how can we be so sure of that ancient date? Even the Greeks and Romans realized that layers of sediment in rock signified old age.
By measuring the ratio of lead to uranium in a rock sample, its age can be determined.
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.
giving a lower limit for the age of the solar system.
Using fossils as guides, they began to piece together a crude history of Earth, but it was an imperfect history.
After all, the ever-changing Earth rarely left a complete geological record.