estone and beds of iron ore are signs of the presence of life. The
first animals and plants lived in the ancient seas.

From the traces that are left, we judge that the earliest life forms
were of the simplest kind, like some plants and animals that swim in a
drop of water. Have you ever seen a drop of pond water under a compound
microscope? It is a wonder world you look into, and you forget all the
world besides. You are one of the wonderful higher animals, the highest
on the earth. You focus on a shapeless creature that moves about and
feels and breathes, but hasn't any eyes or mouth or stomach--in fact, it
is the lowest form of animal life, and one of the smallest. It is but
one of many animal forms, all simple in structure, but able to feed and
grow and reproduce their kind.

Gaze out of the window on the garden, now. The flowering plants, the
green grass, and the trees are among the highest forms of plants. In the
drop of water under the microscope tiny specks of green are floating.
They belong to the lowest order of plants. Among the plant and the
animal forms that have been studied and named, are a few living things
the places of which in the scale are not agreed upon. Some say they are
animals; some believe they are plants. They are like both in some
respects. It is probable that the first living things were like these
confusing, minute things--not distinctly plants or animals, but the
parent forms from which, later on, both plants and animals sprang.

The lowest forms of life, plant and animal, live in water to-day. They
are tiny and their bodies are made of a soft substance like the white of
an egg. If these are at all like the living creatures that swarmed in
the early seas, no wonder they left no traces in the rocks of the early
part of the age when life is first recorded by fossils. Soft-bodied
creatures never do.

Some of the animals and the plants in the drop of water under the
microscope have body walls of definite shapes, made of lime, or of a
glassy substance called silica. When they die, these "skeletons" lie at
the bottom of the water, and do not decay, as the living part of the
body does, because they are mineral. Gradually a number of these shells,
or hard skeletons, accumulate. In a glass of pond water they are found
at the bottom, amongst the sediment. In a pond how many thousands of
these creatures must live and their shells fall to the bottom at last,
buried in the mud!

So it is easy to u