Donna Namiotho, age 12, of Philadelphia, Pa., for her question:

What was the archeozoic era like?

Geologists have divided the age old diary of the earth into chapters called eras. The story began some four billion years ago, and four eras have been completed. The fifth, called the Cenozoic era, began a mere 60 million years ago, and we are still living in it.

The archeozoic era takes us back, way back to the beginning of the history of our planet. The experts try to figure out what it was like from the rocks that were formed in those ancient days. But for more than 500 million years, never and newer rocks have been forming on top of the archeozoic layers. In some places We have to dig a mile or more to reach them. But in other places, nature has made the expert's job easier.

Here and there the earths crust humps to form a ridge of mountains, and sometimes the strain causes a deep crack. If the pushing continues, a massive block of rocky layers may be shoved out of place and slide over the other side of the crack. This brings to the surface the minerals that are buried deep below our feet, and here We are likely to find evidence of what the world was like in this ancient era.

Our world must have been a dull place indeed, but life was just beginning to stir in the fresh Water Seas. There were tiny shell building sea dwellers, perhaps somewhat like the little fellows that formed limestones in later eras. There were miniature water plants, perhaps somewhat like the single celled algae that still swarm in our seas.

The rocks formed in archeozoic times have been crushed under the pressure Of the m8$sive layers above them. Their muddy shales have long since been turned into hard slates, and much of their limestone has become waxy marble. We call these metamorphic rocks, because they have been metamorphized or altered frost their original states.