The Plantae includes all land plants: mosses,
ferns,
conifers,
flowering plants, and so on - an amazing range of diverse forms. With more
than 250,000 species, they are second in size only to the
arthropoda.
Plants have been around for a very long time. The plants first appeared in
the Ordovician,
but did not begin to resemble modern plants until the Late Silurian. By the
close of the
Devonian, about 360 million years ago, there were a wide variety of shapes
and sizes of plants around, including tiny creeping plants and tall forest
trees.
The most striking, and important, feature of plants is their green color, the
result of a pigment called
chlorophyll.
Plants use chlorophyll to capture light energy, which fuels the manufacture of
food—sugar, starch, and other carbohydrates. Without these food sources, most
life on earth would be impossible. There would still be mushrooms and algae, but
there would be no fruits, vegetables, grains, or any animals (which ultimately
rely on plants for their food too!)
Another important contribution of plants is their shaping of the environment.
Think of a place without plants. The only such places on earth are the arctic
wastelands, really arid deserts, and the deep ocean. Everywhere else, from the
tundra to the rainforest to the desert, is populated by plants. In fact, when we
think of a particular landscape, it is the plants which first come to mind. Try
to picture a forest without trees, or a prairie without grasses. It is the
plants which produce and maintain the terrestrial environment as we know it.
The Paleozoic is bracketed by two of the most important events in the history
of animal life. At its beginning, multicelled animals underwent a dramatic
"explosion" in
diversity, and almost all living
animal phyla
appeared within a few millions of years. At the other end of the Paleozoic, the
largest mass extinction in history wiped out approximately 90% of all marine
animal species. The causes of both these events are still not fully understood
and the subject of much research and controversy. Roughly halfway in between,
animals,
fungi, and
plants alike
colonized the land, the
insects
took to the air, and the limestone shown in this picture was deposited near
Burlington, Missouri.
The Paleozoic took up over half of the Phanerozoic, approximately 300
million years. During the Paleozoic there were six major continental land
masses; each of these consisted of different parts of the modern continents. For
instance, at the beginning of the Paleozoic, today's western coast of North
America ran east-west along the equator, while Africa was at the South Pole.
These Paleozoic continents experienced tremendous mountain building along their
margins, and numerous incursions and retreats of shallow seas across their
interiors. Large limestone outcrops, like the one shown above, are evidence of
these periodic incursions of continental seas.
Many Paleozoic rocks are economically important. For example, much of the
limestone quarried for building and industrial purposes, as well as the
coal deposits of western Europe and the eastern United States, were formed
during the Paleozoic.
