They observed that every rock formation, no matter how ancient, appeared to be formed from still older rocks.
Comparing these rocks with the products of present erosion, sedimentation, and earth movements, these earliest geologists soon concluded that the time required to form and sculpt the present Earth was immeasurably longer than had previously been thought.
The methods work because radioactive elements are unstable, and they are always trying to move to a more stable state. This process by which an unstable atomic nucleus loses energy by releasing radiation is called radioactive decay.
The thing that makes this decay process so valuable for determining the age of an object is that each radioactive isotope decays at its own fixed rate, which is expressed in terms of its half-life.
he question of the ages of the Earth and its rock formations and features has fascinated philosophers, theologians, and scientists for centuries, primarily because the answers put our lives in temporal perspective.
Until the 18th century, this question was principally in the hands of theologians, who based their calculations on biblical chronology.
James Joly calculated that the Earth’s age was 89 million years on the basis of the time required for salt to accumulate in the oceans.Most people think that radioactive dating has proven the earth is billions of years old.After all, textbooks, media, and museums glibly present ages of millions of years as fact.To achieve stability, some ‘particles’ are ejected from the atoms, and these moving ‘particles’ constitute the radioactivity measured by Geiger counters and the like.The end result is stable atoms of the ‘daughter’ elements lead, argon, and strontium respectively.