Photo Gallery: Carboniferous Period
Characteristic of the Carboniferous period (from about 360 million to 300 million years ago) were its dense and swampy forests, which gave rise to large deposits of peat. Over the eons the peat transformed into rich coal stores in Western Europe and North America. The name "Carboniferous" refers to this coal.
Perfectly preserved for more than 300 million years, a horsetail carries secrets from the Carboniferous period. Primitive vascular plants, horsetails (genus Equisetum) are often found in coal deposits.
The Carboniferous period saw the appearance of the first extensive forests on Earth. The growth of these forests removed huge amounts of carbon dioxide from the atmosphere, leading to a surplus of oxygen. Atmospheric oxygen levels peaked around 35 percent, compared to 21 percent today.
From : Nationalgeographic