Melissa Burelli, age 11, of Merrillville, Indiana, for her question:

What were the first plants like?

The earth's first plants left no fossil remains so we can only guess what they were like. However, we can make an educated guess, based on indirect evidence. Scientists agree that life on the planet Earth began with very simple designs that gradually, very gradually grew more complex. In many cases, the simplified ancestors continued to survive while other life forms became more sophisticated. Most likely some of the simplest living plants are very similar to the original old timers.

The modern world is clothed with a green mantle of more than 350,000 different plants. The multi green mantle is fringed and tasseled with grasses and vines, clustered with nuts and seeds and berries and gaily embroidered with at least 200,000 different blossoms. But all this wondrous beauty did not happen in a hurry. Scientists suspect that the patient story started in a very small way    perhaps four billion years ago.

We can be pretty sure that the earth's first plants were at home in the watery seas. We can also assume that nature followed her usual plans, in which case, the first plants would be tiny single celled organisms. Right from the start, they must have been able to manufacture their basic supplies from plentiful raw materials around them. Almost certainly, they use the energy of sunlight to manufacture their basic food from carbon dioxide, water and dissolved chemicals.

A floating, single celled plant of this sort is not hard to imagine. It so happens that zillions just like it still drift in the salty seas and also in fresh inland waters. They are the simple, one celled algae that still populate the waters of the world. Most scientists suspect that these modern midgets are very similar to the first plants that appeared on earth, perhaps four billion years ago.

Naturally those tiny specks of tender living tissue were too fragile to leave fossils or even imprints in the ancient rocks. However, their busy cells carried on the complex chemical processes of life.

Some experts suggest that certain deposits of iron and graphite may have been modified by ancient plant life. Some also suspect that decomposing early water plants may have contributed to underground deposits of petroleum.

However, though we can make some educated guesses, we cannot be certain about the plant world's first billion years or so. We can assume that during this period some of the original midgets became multi celled plants. They were small, simple alga types, stemless and rootless  ¬and three billion years ago they left us our first fossil record of the plant world.

At long last, the early plants were joined by the earth's first simple animals. For ages and ages they shared the ancient seas. Then, about 435 million years ago, a few stranded water weeds managed to survive on the beaches. In time, their descendants developed roots and sturdy stems, seeds and finally flowers. Our wondrous modern plant world was established about 26 million years ago.