Coal beds, which can be up to 11 to 12 ters thick, characterize the late Carboniferous. The forests of seedless vascular plants that existed in the tropical swamp forests of Europe and North Arica provided the organic material that beca coal.
Dead plants did not completely decay and were turned to peat in these swamp forests. When the sea covered the swamps, marine sedints covered the peat. Eventually, heat and pressure transford these organic remains into coal. Coal balls, pockets of plant debris that were preserved as fossils and not converted to coal, are sotis found within the coal layers.
Multiple transgressions and regressions of the Pennsylvanian seas across the continent can be seen in the rocks, and even counted, because they leave a telltale sequence of layers. As sea levels rise, the layers may go from sandstone (beach), to silty shale or siltstone (tidal), to freshwater listone (lagoon), to underclay (terrestrial), to coal (terrestrial swampy forest). Then as sea levels fall, one may see a shale (nearshore tidal) grade to listone (shallow marine) and finally to black shale (deep marine).
Index fossils are the remains of plants and animals that characterize a well-defined ti span and occur over a wide range of geography. Fossils of marine life characterize the Mississippian, as shallow epicontinental seas covered the United States at that ti.
These fossils include solitary corals and Syringopora, tubular colonial corals. Other fossil colonial corals include Stelechophyllum and Siphonodendron. Because conodont fossils are distributed all over the world, they are utilized internationally to date Mississippian rocks.
Index fossils used for the Pennsylvanian Subsystem are fusulinid foraminifers and the pollen and spores from the coal forests prevalent during that ti.
The Mississippian-Pennsylvanian boundary is marked by the appearance of the fusulinid Pseudostaffella antiqua. Other fossils used to identify the early Pennsylvanian are the three ammonoid cephalopod genera Gastrioceras, Daiboloceras, and Paralegoceras, all found in marine deposits.
After completing this one next on line was Permian Period. Which was a major evolutionary period in the geographical tiline of earth.
The Permian Period was the final period of the Paleozoic Era. Lasting from 299 million to 251 million years ago, it followed the Carboniferous Period and preceded the Triassic Period.
By the early Permian, the two great continents of the Paleozoic, Gondwana and Eurarica, had collided to form the supercontinent Pangaea. Pangaea was shaped like a thickened letter "C."
The top curve of the "C" consisted of landmasses that would later beco modern Europe and Asia. North and South Arica ford the curved back of the "C" with Africa inside the curve.
India, Australia and Antarctica made up the low curve. Inside the "C" was the Tethys Ocean, and most of the rest of Earth was the Panthalassic Ocean. Because Pangaea was so imnse, the interior portions of the continent had a much cooler, drier climate than had existed in the Carboniferous.
Little is known about the huge Panthalassic Ocean, as there is little exposed fossil evidence available. Fossils of the shallower coastal waters around the Pangaea continental shelf indicate that reefs were large and diverse ecosystems with nurous sponge and coral species.
Ammonites, similar to the modern nautilus, were common, as were brachiopods. The lobe-finned and spiny fishes that gave rise to the amphibians of the Carboniferous were being replaced by true bony fish. Sharks and rays continued in abundance.
On land, the giant swamp forests of the Carboniferous began to dry out. The mossy plants that depended on spores for reproduction were being replaced by the first seed-bearing plants, the gymnosperms.
Gymnosperms are vascular plants, able to transport water internally. Gymnosperms have exposed seeds that develop on the scales of cones and are fertilized when pollen sifts down and lands directly on the seed. Today's conifers are gymnosperms, as are the short palm like cycads and the gingko.
During this ti arthropods continued to diversify during the Permian Period to fill the niches opened up by the more variable climate. True bugs, with mouthparts modified for piercing and sucking plant materials, evolved during the Permian. Other new groups included the cicadas and beetles.
Two important groups of animals dominated the Permian landscape: Synapsids and Sauropsids. Synapsids had skulls with a single temporal opening and are thought to be the lineage that eventually led to mammals. Sauropsids had two skull openings and were the ancestors of the reptiles, including dinosaurs and birds.
In the early Permian, it appeared that the Synapsids were to be the dominant group of land animals. The group was highly diversified. The earliest, most primitive Synapsids were the Pelycosaurs, which included an apex predator, a genus known as Ditrodon.
This animal had a lizard-like body and a large bony "sail" fin on its back that was probably used for thermoregulation.
Despite its lizard-like appearance, recent discoveries have concluded that Ditrodon skulls, jaws and teeth are closer to mammal skulls than to reptiles.
Another genus of Synapsids, Lystrosaurus, was a small herbivore about 3 feet long (almost 1 ter) that looked sothing like a cross between a lizard and a hippopotamus. It had a flat face with two tusks and the typical reptilian stance with legs angled away from the body.
In the late Permian, Pelycosaurs were succeeded by a new lineage known as Therapsids. These animals were much closer to mammals. Their legs were under their bodies, giving them the more upright stance typical of quadruped mammals.
They had more powerful jaws and more tooth differentiation. Fossil skulls show evidence of whiskers, which indicates that so species had fur and were endothermic. The Cynodont ("dog-toothed") group included species that hunted in organized packs. Cynodonts are considered to be the ancestors of all modern mammals.
At the end of the Permian, the largest Synapsids beca extinct, leaving many ecological niches open. The second group of land animals, the Sauropsid group, weathered the Permian Extinction more successfully and rapidly diversified to fill them. The Sauropsid lineage gave rise to the dinosaurs that would dominate the sozoic Era.
The Permian Period ended with the greatest mass extinction event in Earth's history. In a blink of Geologic Ti in as little as 100,000 years the majority of living species on the planet were wiped out of existence. Scientists estimate that more than 95 percent of marine species beca extinct and more than 70 percent of land animals. Fossil beds in the Italian Alps show that plants were hit just as hard as animal species. Fossils from the late Permian show that huge conifer forests blanketed the region. These strata are followed by early Triassic fossils that show few signs of plants being present but instead are filled with fossil remnants of fungi that probably proliferated on a glut of decaying trees.
Scientists are unclear about what caused the mass extinction. So point to evidence of catastrophic volcanic activity in Siberia and China (areas in the northern part of the "C" shaped Pangaea).
This series of massive eruptions would have initially caused a rapid cooling of global temperatures leading to increased glaciations.
This "nuclear winter" would have led to the demise of photosynthetic organisms, the basis of most food chains.
Lowered sea levels and volcanic fallout would account for the evidence of much higher levels of carbon dioxide in the oceans, which may have led to the collapse of marine ecosystems.
Other scientists point to indications of a massive asteroid impacting the southernmost tip of the "C" in what is now Australia. Whatever the cause, the Great Dying closed the Paleozoic Era.
After the great extinction it was the ti of a new beginning, the sozoic era. During the sozoic, or "Middle Life" era, life diversified rapidly and giant reptiles, dinosaurs and other monstrous beasts road the Earth. The period, which spans from about 252 million years ago to about 66 million years ago, was also known as the age of reptiles or the age of dinosaurs.
The sozoic era began roughly around the ti of the end-Permian extinction, which wiped out 96 percent of marine life and 70 percent of all terrestrial species on the planet. Life slowly rebounded, eventually giving way to a flourishing diversity of animals, from massive lizards to monstrous dinosaurs.
The Triassic period, from 252 million to 200 million years ago, saw the rise of reptiles and the first dinosaurs. The Jurassic period, from about 200 million to 145 million years ago, ushered in birds and mammals. And the Cretaceous period, from 145 million to 66 million years ago is known for its iconic dinosaurs, such as Triceratops, and pterosaurs such as Pteranodon.
Coniferous plants, or those that have cone-bearing seeds, already existed at the beginning of the era, but they beca much more abundant during the sozoic. Flowering plants erged during the late Cretaceous period. The lush plant life during the sozoic era provided plenty of food, allowing the biggest of the dinosaurs, such as the Argentinosaurus, to grow up to 80 tons, according to a 2005 study in the journal Revista del Museo Argentino de Ciencias Naturales.
Earth during the sozoic era was much warr than today, and the planet had no polar ice caps. During the Triassic period, Pangaea still ford one massive supercontinent. Without much coastline to moderate the continent's interior temperature, Pangaea experienced major temperature swings and was covered in large swaths of desert.
Yet the region still had a belt of tropical rainforest in regions around the equator, said Brendan Murphy, an earth scientist at St. Francis Xavier University in Antigonish, Canada.
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