The expansion of the universe gives an age for the universe as a whole: 13.7 billion years old.
Astronomers and geologists have determined that the universe and Earth are billions of years old.
There are many ways to keep track of time, the most reliable of which is to use actual records such as counting hours, days, weeks, and years.
However, when we speak of the distant past, there are no historical records and thus no verifiable way to prove that a certain 'date' is correct.
After the passage of two half-lives only 0.25 gram will remain, and after 3 half lives only 0.125 will remain etc.Many independent measurements have established that the Earth and the universe are billions of years old.Geologists have found annual layers in ice that are easily counted to multiple tens of thousands of years, and when combined with radio isotope dating, we find hundreds of thousands of years of ice layers.The age of the carbon in the rock is different from that of the carbon in the air and makes carbon dating data for those organisms inaccurate under the assumptions normally used for carbon dating.This restriction extends to animals that consume seafood in their diet.There are at least 67 different uniformitarian (the present is the key to the past) methods of dating the earth other than long-age radiometric dating: each of which yield ages of less than 500 million years.