Isochron dating site
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.After Henri Becquerel's initial discovery in 1896, Marie and Pierre Curie discovered the radioactive elements polonium and radium in 1898; and in 1903, Pierre Curie and Albert Laborde announced that radium produces enough heat to melt its own weight in ice in less than an hour.
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.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.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.
However, they assumed that the Sun was only glowing from the heat of its gravitational contraction.