Richard McCarter age 13, of Philadelphia, Penna, for his question:

How can they tell the age of the earth?

In the early 18001s, almost any learned scholar would have told you that the earth was about 6,000 years old. He reached this estimate by totting up events in the Bible. And, as people so often dos he misunderstood this greatest of all books. After all, how long is a day? Is it 12 hours of daylight or a 24‑hour date on a calendar? What do we mean when we say something was common in grandmotherts day? How long a period was the day of the dinosaurs?

In common speech a day is a period of time varying from 12 hours or less to millions of years. Some people tend to forget this when they interpret the Great Book. The early geologists forgot that a day could also mean a period covering millions of years, Their estimate of the earths age was far, far too short.

Around 1840 a young Swiss professor became interested in the glacial damage done to the Alps. His studies led to the discovery of the Ice Ages, when glaciers covered vast areas of the land. Tha evidence showed that these glaciers occured long, long before 6,000 years ago, Experts began to realize that the earth was far older than they had supposed.

They set to work to make a more accurate estimate. One group worked out an estimated age from studying the seas. They figured it from the amount of salt added to the oceans each year. It took at least 100 million years for the sea to gather its salt from the land. If the oceans were this old: then the land must be older still.

Then radioactivity was discovered, Science learned that certain rocks constant were in a state of decay. Uranium 238 and other radioactive elements are in the process of becoming lead, The process is a slows steady chain reaction of larger atoms breaking into smaller atoms, step by step.

This radioactivity in certain natural rocks cannot be slowed down or hurried. In four and one half billion years exactly half of any quantity of uranium will of uranium will decay. In the next four and and a half billion years, exactly half of the remaining uranium will decay. This decaying process repeats and repeats on schedule. We say thnt four and one half billion years is the half life of uranium, in which time half the supply will decay by radioactivity.

The end product of radioactive decay is a special kind of lead. A certain amount of this lead is always found in naturally radioactive rocks. And these rocks occur herd and there throughout the earth's crust. This special lead, in proportion to the radioactive content, tells how long the decay has been in process end hence the age of the rock.

Radioactivity is the most up‑to‑date method for estimating the age of the earth. Certain rocks found in Manitoba reveal their radioactive age as 2.3 billion yours. This method shows the solid crust of the north to be between two and throe billion yenrs. The true ago of the earth must be greater, not less, than this. Our planet, like any lovely lady, does not make it easy for us to estimate the exact number of her birthdys.