Lynn Smithf aged 13, of Peoria, Illinois, for her question

What is a fossil?

The old earth, it seems, keeps a diary. It is written in age long chapters dating back millions of years. The pages of the diary are the rocky layers of her crust. From time to time she keeps a specimen of this creature or that. The bones of some ancient creature are preserved deep in the rocky pages. A footprint is saved forever in hardened mud. The imprint of a feather or shell is saved through the long ages.

Sometimes the earth presses plant specimens between the pages of her diary. She does these things in a big way. Whole forests are pressed and saved deep in the rocky ground. We call them beds of coal. They are some of the most valuable fossils.

Leonardo da Vinci was a great painter of the sixteenth century. He was also one of the most thoughtfully curious men who ever lived. He was puzzled by some shell‑like designs in certain stones with which he worked, And Leonardo was, one of the first to recognize these things for what they were, They were, he thought, the relics of bygone animals.

We call all these preserved specimens fossils. The word fossil comes from an older word meaning to dig up. This is because fossils are usually found deep in the ground. Dead bodies of animals soon decay in the open air. In order to become a fossil, a creature must be buried in some way.

Only so can it be preserved. It may be buried in the wet mud of a sea bed or under piles of dry earth. But it will not endure if its burial place tends to change from wet to dry,

Some fossils are preserved in ice. A fossilized mammoth was found in the glacial ice of Siberia. Its bones, its flesh and most of its skin were preserved in an age‑old deep freeze.

The most perfect fossils are preserved in amber. Such a fossil started when some insect became trapped in the sticky resin given off by an ancient tree. In time, the resin hardened into a glob of golden amber. The little creature was trapped forever in a glassy tomb. Sometimes these creatures are so perfectly preserved that we can see their delicate wings and fine hairs.

Most fossils, however, are the buried bones of animals who lived on earth long, long ago. Experts study them to see what kind of creatures once lived and died here, They can trace back the history of life on earth. The floor of an old cave is a good place to dig for such fossils. Many are found preserved in beds of asphalt. Old volcanic vents often yield up fossil bones. Animals fell into holes and tar pits and were buried there.

Sometimes the remains of plants and animals become turned into stone. There are such petrified bones, shells and trees. This work is done by running water. Each particle is replaced by stony; chemical, It is a long job, When it is done, a perfect copy of the original creature or plant exists in stone, sometimes in precious opal, Strictly speaking, these petrified objects are not fossils. But they often tell us as much about the ancient world as does a real fossil.