05/01/2012 · From the Contracting Earth to ..
EARTH520 Contracting Earth Hypothesis - YouTube
Artists have been depicting Carboniferous swamps for more than a century, and the . That represents a key Carboniferous issue and perhaps why the period ended. That , and others like it, appeared in the fossil record about 300 mya, when oxygen levels were Earth’s highest ever, at somewhere between 25% and 35%. The almost universally accepted reason for that high oxygen level is that for the entire Carboniferous Period removed carbon dioxide from the atmosphere in vast amounts. Today, the estimate is that carbon dioxide fell from about 1,500 PPM at the beginning of the Carboniferous to 350 PPM by the end, which is lower than today’s value. That tandem effect of sequestering carbon and freeing oxygen not only may have led to huge arthropods and amphibians, but also intensified . The idea that high oxygen levels led to those giants was first proposed more than a century ago and dismissed, but has recently come back into favor. Flying insects have the highest metabolisms of all animals, but they do not have diaphragmatic lungs as mammals have, or air sac lungs as birds have, and although they may have some way of actively breathing by contracting their tracheas, it is not the bellows action of vertebrate lungs. The for early insect gigantism is that high oxygen, as well as a denser atmosphere (the nitrogen mass would not have fallen, so increased oxygen would have added to the atmosphere’s mass), would have enabled such leviathans to fly, and the other is that flying insects got a head start in the arms race and could grow large until predators that could catch them evolved. The late Permian had an even larger dragonfly, when oxygen levels had crashed back down. The evolution of flight is another area of great controversy, and insects accomplished it long before vertebrates did. The general idea is that flight structures evolved from those used for other purposes. For insects, wings appear to have evolved from aquatic “oars,” and gills became lungs. Reptiles did not develop flight until the Triassic, and .
contracting Earth hypothesis - oi - Oxford Index Home
When the beginning about 307 mya, Earth’s oxygen levels were at their highest ever. About 75% of Earth’s coal deposits were formed in the Carboniferous, with most of it laid down in the 25-million-year Pennsylvanian Epoch. There will never be a coal-forming period like that again on Earth, as organisms about 290 mya. Even if humans burned all fossil fuel deposits, carbon dioxide levels will never again reach the levels that preceded the Carboniferous, at many times today’s concentrations.