Betty Zelcovitz, Age 14, of Philadelphia, PA., and Audry Lee Strong, Age 16, of Winterweld, Georgia, for their questions:

How is carbon 14 used to date objects?

It took billions of years to prepare this luxury planet for the race of man the curious. Strange to say, the records of the age long preparations for his home are preserved in the rocks of the earth’s crust. When at last we become smart enough and brave enough they were there for us to read. Sometimes, as in the case of carbon 14, our.,scientists have to use their best brains to figure out the code in which the old records are written.

Carbon 14 is a radioactive substance and the secrets of radioactivity were cracked at the close of the last century by the Curies, a husband and wife team of scientists working together. Many other scientists enlarged on their work and the useful qualities, of carbon 14 were discovered only in 19.7. The atomic weight of ordinary carbon is 12 and among the countless ordinary carbon atoms in the world there are a number of carbon atoms with extra neutron particles which give them the extra weight.

These overweight. atoms are isotopes and carbon its is a carbon isotope with two extra neutrons. These extra neutrons in the nucleus upset the balance of the atom and make it unstable. In time, the overweight nucleus of carbon l4 bursts with a spurt of radio active energy. , leaving behind an atom of ordinary everyday carbon.

Now carbon is a very common S element in our world. It is used in the making of all plant and animal life .and it stays right there in the cells long after the plants and animals have ceased to live, About_one carbon atom in every trillion is an isotope of carbon 14. The isotopes trapped in the remains of once living things continue to decay by radioactivity  and they decay at an absolutely fixed rate.

After 5,600 years exactly half of the carbon 14 atoms have decayed. When we find that a fossil tree contains half the percentage of carbon 14 atoms found in a living tree, we know that it stopped its life processes about 5,600 years ago. In the next 5,600 years exactly half of the remaining carbon 14 will decay. For this reason we say that carbon 14 has a half life of about 5,600 years. With time, the evidence of this radioactive decay becomes weaker, but with delicate instruments scientists can test the carbon 14 decay still going on in ancient fossils and from this they can date the age of fossil plant and animal remains.

Carbon 14 is a radioactive calendar which can give us accurate dates to about 50,000 years ago. This is but recant history in the age. old story of our planet. Other radioactive calendars take the probing scientists even farther back into the records. One of these is the recently discovered potassium argon test. This radioactive calendar can be used to data the age of rooks formed billions of years ago.