This means that after approximately 4.5 billion years, half of an original sample containing this isotope will decay into its decay product, forming the new isotope, Pb 206 (lead 206).
If another 4.5 billion years were to pass, then half of the remaining half of uranium-238 would also decay, leaving 25% uranium to 75% lead.
The half-life is so predictable that it is also referred to as an atomic clock.
Can you guess how much uranium-238 would remain after the passing of another half-life?
When an atom varies in the number of neutrons, the variation is called an isotope. During radioactivity, the unstable isotope breaks down and changes into a different substance.
A new, more stable isotope, called the decay or daughter product, takes its place.
An isotope disintegrates at a constant rate called the half-life --the time it takes for half the atoms of a sample to decay. By counting the number of half-lives and the percentages remaining of parent and daughter isotopes, scientists are able to determine what they call the absolute age of a discovery.
two half-lives went by at a rate of 4.5 billion years per half-life; therefore, the sample is approximately 2 times 4.5 billion or 9 billion years old. So you see, Earth scientists are able to use the half-lives of isotopes to date materials back to thousands, millions and even to billions of years old.Ever wonder how scientists concluded the age of the earth to be about 4.6 billion years old or how geologists determined the ages of caverns, rocks, volcanoes and the Himalayas? Well, scientists are able to answer all of these wondrous questions and more by use of a process called radiometric or radioactive dating.