A child mummy is found high in the Andes and the archaeologist says the child lived more than 2,000 years ago.How do scientists know how old an object or human remains are?

­ ­You probably have seen or read news stories about fascinating ancient artifacts.

At an ar­chaeological dig, a piece of wooden tool is unearthed and the archaeologist finds it to be 5,000 years old.

A plot is constructed of Pb-206/Pb-204 versus Pb-207/Pb-204.

If the solar system formed from a common pool of matter, which was uniformly distributed in terms of Pb isotope ratios, then the initial plots for all objects from that pool of matter would fall on a single point.

What methods do they use and how do these methods work?

In this article, we will examine the methods by which scientists use radioactivity to determine the age of objects, most notably carbon-14 dating.

Further, the processes of erosion and crustal recycling have apparently destroyed all of the earliest surface.

The oldest rocks which have been found so far (on the Earth) date to about 3.8 to 3.9 billion years ago (by several radiometric dating methods).

The most direct means for calculating the Earth's age is a Pb/Pb isochron age, derived from samples of the Earth and meteorites.

This involves measurement of three isotopes of lead (Pb-206, Pb-207, and either Pb-208 or Pb-204).

Note that young-Earthers cannot accuse us of selective use of data -- the above table includes a significant fraction of all meteorites on which isotope dating has been attempted. 286) , less than 100 meteorites have been subjected to isotope dating, and of those about 70 yield ages with low analytical error.