Beth Crawley, age 11, of Casper, Wyo., for her question:
WHEN DID THE FIRST FOREST DEVELOP?
Scientists tell us that the first forests of the earth developed in marshlands about 365 million years ago, during the Devonian Period. They consisted of tree sized mosses and ferns, some of which had trunks nearly 40 feet high and about three feet thick.
These first forests then became the home of the first amphibians and insects.
By the start of the Carboniferous Period about 345 million years ago vast swamps covered much of North America. Forests of giant club mosses and horsetails up to 125 feet tall grew in these warm swamps.
Ferns about 10 feet tall formed a thick underground that sheltered huge cockroaches, dragonflies, scorpions and spiders in these early forests. In time, seed ferns and primitive conifers developed in the swamp forests.
When plants of the swamp forests died, they fell into the mud and water that covered the forest floor. The mud and water did not contain enough oxygen to support decomposition. As a result, the fallen plants did not decay but became buried under layer after layer of mud. Over millions of years, the weight and pressure on the dead plants turned them into great coal deposits.
The Mesozoic Era started about 225 million years ago. Severe changes in climate and in the earth's surface wiped out the swamp forests. In the new, drier environment, gymnosperm trees became dominant. Gymnosperms are plants whose seeds are not enclosed in a fruit or pod.
The gymnosperm trees included seed ferns and primitive conifers like those that grew in the swamp forests. But they also included cycad and ginko trees which became widespread.
The first flowering plants appeared about 130 million years ago, during the Cretaceous Period. Flowering plants, which are called angiosperms, produce seeds enclosed in a fruit or seedcase. Angiosperm trees included magnolias, maples, poplars and willows.
Flowering shrubs and herbs became common undergrowth plants.
At the start of the Cenozoic Era, about 65 million years ago, the earth's climate turned cooler. Magnificent temperate forests then spread across North America, Europe and Asia. The forests included a wealth of flowering broadleaf trees and needleleaf conifers. Many birds and mammals lived in these forests.
About a million and a half years ago, the earth's climate continued to turn colder and the Pleistocene Ice Age started. Several great waves of glaciers advanced over much of North America and Europe and then retreated.
By the time the last great glacier retreated about 10,000 years ago the ice sheets had destroyed large areas of the temperate forests of North America and Europe. Only the temperate forests of southeastern Asia remained largely untouched.
The forests of the world took on their modern distribution after the Ice Age came to an end.