Welcome to You Ask Andy

Craig Houch, age 12, of Lancaster, Pa., for his question:

Is it true that the earth is more than a million years old?

It took the earth more than a million years to fill her watery oceans. This big job had to be finished before the first little plants and animals could survive. And they arrived more than a billion years ago. Some of the lovely old mountains in Pennsyl¬vania started growing 200 million years ago. These ancient events tell us that our wondrous planet is indeed very, very much older than one million years.

No doubt you have seen those glamorous portraits of the earth, taken from outer space. Its round globe is tinted with brown green continents and frosty ice caps, set in the sparkling silver blue seas. Surely, you would think, this is the space portrait of a gorgeous young planet.

We get the same idea when we behold its beauties from down here on the ground. True, the world looks somewhat old and worn at summer's end, when the wide outdoors is strewn with fallen leaves and faded flowers. But in a few short months, spring comes, and our wintery old world is renewed and becomes a lovely young lady or so it seems.

As you know, a lovely lady often strives very hard indeed to conceal her true age. So it is with the earth. Generations of scientists strained their brains to solve this problem    and they still cannot give the exact age of the earth. The evidence is there, most of it in buried rocks. But it is concealed very cunningly in secret codes.

For example, scientists learned that the sea is getting saltier, year by year. A century ago, they used this data to estimate the age of the oceans. It took the sea many millions of years to steal all its salts from the land. And obviously the earth must be older than its oceans.

In the 1800s, a geologist traced the havoc left by ancient glaciers. In the last million years, four ice ages came and went in our hemisphere. Evidence of earlier ice ages was found elsewhere. One occurred 500 million years ago. Obviously the earth is older than its ice ages.

'Modern scientists are using newer methods to solve the well kept secret. For example, most rocks contain traces of radioactive materials that decay at a fixed rate. By measuring these slight but dependable changes it is possible to estimate the age of ancient rocks. The oldest rocks found so far were formed three and a half billion years ago. Scientists estimate teat the earth must be a billion tears older than its oldest surviving rocks. So our best guess is that our planet has celebrated 4500 million birthdays  which adds up to four and a half billion years.

Another line of investigation, strange to say, is out in space. The sun, its planets and their satellites are related in an orderly system. A lot of evidence, plus a lot of common sense, indicates that the whole thing originated at more or less the same time. In this case, the earth's crust would be the same age as the moon    where parts of the original surface may be exposed or near the surface. As you know, scientists are very eager to date these ancient lunar rocks. If some prove to be older than four and a half billion years, then most likely our glamorous earth is even older than we thought.

 

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