The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago, to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, where rocks from this period were first studied; the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods became well-established. Fish reached substantial diversity during this time, leading the Devonian to be dubbed the "Age of Fishes." The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating every known aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral and pelvic fins evolved into legs.
In the oceans, primitive sharks became more numerous than in the Late Ordovician. The first ammonites, species of molluscs, appeared. Trilobites, the mollusc-like brachiopods and the great coral reefs, were still common; the Late Devonian extinction which started about 375 million years ago affected marine life, killing off all placodermi, all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, the early formation of the small continent of Euramerica in between; the period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found distributed throughout the county was resolved by the definition of the Devonian period in the geological timescale. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough.
Murchison and Sedgwick named the period they proposed as the Devonian System. While the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, to the beginning of the Carboniferous 358.9 Mya. In nineteenth-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is "Age of the Fishes", referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian and Farlovian stages, the latter three of which are placed in the Devonian; the Devonian has erroneously been characterised as a "greenhouse age", due to sampling bias: most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America, which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid but in fact the climate in the Devonian differed during its epochs and between geographic regions.
For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, North America, China, but Africa and South America had a warm temperate climate. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common; the Devonian Period is formally broken into Early and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower and Upper parts of the Devonian System. Early DevonianThe Early Devonian lasted from 419.2 ± 2.8 to 393.3 ± 2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ± 2.8 to 407.6 ± 2.5, was followed by the Emsian, which lasted until the Middle Devonian began, 393.3± 2.7 million years ago. During this time, the first ammonoids appeared. Ammonoids during this time period differed little from their nautiloid counterparts; these ammonoids belong to the order Agoniatitida, which in epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida.
This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic era. Middle DevonianThe Middle Devonian comprised two subdivisions: first the Eifelian, which gave way to the Givetian 387.7± 2.7 million years ago. During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments due to drastic environmental changes and due to the increasing competition and diversity of jawed fishes; the shallow, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop such essential characteristics as well developed lungs, the ability to crawl out of the water and onto the land for short periods of time. Late DevonianFinally, the Late Devonian started with the Frasnian, 382.7 ± 2.8 to 372.2 ± 2.5, during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing Famennian subdivisi
Mississippi is a state located in the southeastern region of the United States. Mississippi is the 32nd most 34th most populous of the 50 United States, it is bordered by Tennessee to the north, Alabama to the east, the Gulf of Mexico and Louisiana to the south, Arkansas and Louisiana to the west. The state's western boundary is defined by the Mississippi River. Jackson, with a population of 167,000 people, is both the state's capital and largest city; the state is forested outside the Mississippi Delta area, the area between the Mississippi and Yazoo rivers. Before the American Civil War, most development in the state was along riverfronts, as the waterways were critical for transportation. Large gangs of slaves were used to work on cotton plantations. After the war, freedmen began to clear the bottomlands to the interior, in the process selling off timber and buying property. By the end of the 19th century, African Americans made up two-thirds of the Delta's property owners, but timber and railroad companies acquired much of the land after the financial crisis, which occurred when blacks were facing increasing racial discrimination and disfranchisement in the state.
Clearing of the land for plantations altered the Delta's ecology, increasing the severity of flooding along the Mississippi by taking out trees and bushes that had absorbed excess waters. Much land is now held by agribusinesses. A rural state with agricultural areas dominated by industrial farms, Mississippi is ranked low or last among the states in such measures as health, educational attainment, median household income; the state's catfish aquaculture farms produce the majority of farm-raised catfish consumed in the United States. Since the 1930s and the Great Migration of African Americans to the North and West, the majority of Mississippi's population has been white, although the state still has the highest percentage of black residents of any U. S. state. From the early 19th century to the 1930s, its residents were majority black, before the American Civil War that population was composed of African-American slaves. Democratic Party whites retained political power through disfranchisement and Jim Crow laws.
In the first half of the 20th century, nearly 400,000 rural blacks left the state for work and opportunities in northern and midwestern cities, with another wave of migration around World War II to West Coast cities. In the early 1960s, Mississippi was the poorest state in the nation, with 86% of its non-whites living below the poverty level. In 2010, 37% of Mississippians were African Americans, the highest percentage of African Americans in any U. S. state. Since regaining enforcement of their voting rights in the late 1960s, most African Americans have supported Democratic candidates in local and national elections. Conservative whites have shifted to the Republican Party. African Americans are a majority in many counties of the Mississippi-Yazoo Delta, an area of historic slave settlement during the plantation era; the state's name is derived from the Mississippi River. Settlers named it after the Ojibwe word misi-ziibi. Mississippi is bordered to the north by Tennessee, to the east by Alabama, to the south by Louisiana and a narrow coast on the Gulf of Mexico.
In addition to its namesake, major rivers in Mississippi include the Big Black River, the Pearl River, the Yazoo River, the Pascagoula River, the Tombigbee River. Major lakes include Ross Barnett Reservoir, Arkabutla Lake, Sardis Lake, Grenada Lake with the largest lake being Sardis Lake. Mississippi is composed of lowlands, the highest point being Woodall Mountain, in the foothills of the Cumberland Mountains, 807 feet above sea level; the lowest point is sea level at the Gulf Coast. The state's mean elevation is 300 feet above sea level. Most of Mississippi is part of the East Gulf Coastal Plain; the coastal plain is composed of low hills, such as the Pine Hills in the south and the North Central Hills. The Pontotoc Ridge and the Fall Line Hills in the northeast have somewhat higher elevations. Yellow-brown loess soil is found in the western parts of the state; the northeast is a region of fertile black earth. The coastline includes large bays at Bay St. Louis and Pascagoula, it is separated from the Gulf of Mexico proper by the shallow Mississippi Sound, sheltered by Petit Bois Island, Horn Island and West Ship Islands, Deer Island, Round Island, Cat Island.
The northwest remainder of the state consists of the Mississippi Delta, a section of the Mississippi Alluvial Plain. The plain widens north of Vicksburg; the region has rich soil made up of silt, deposited by the flood waters of the Mississippi River. Areas under the management of the National Park Service include: Brices Cross Roads National Battlefield Site near Baldwyn Gulf Islands National Seashore Natchez National Historical Park in Natchez Natchez Trace National Scenic Trail in Tupelo Natchez Trace Parkway Tupelo National Battlefield in Tupelo Vicksburg National Military Park and Cemetery in Vicksburg Mississippi City Population Rankings of at least 50,000: Mississippi City Population Rankings of at least 20,000 but fewer than 50,000: Mississippi City Population Rankings of at least 10,000 but fewer than 20,000: Mississippi has a humid
The American alligator, sometimes referred to colloquially as a gator or common alligator, is a large crocodilian reptile endemic to the southeastern United States. It is one of two living species in the genus Alligator within the family Alligatoridae. Adult male American alligators measure 3.4 to 4.6 m in length, can weigh up to 453 kg. Females are smaller; the American alligator inhabits freshwater wetlands, such as marshes and cypress swamps from Texas to southeastern and coastal Virginia. It is distinguished from the sympatric American crocodile by its broader snout, with overlapping jaws and darker coloration, is less tolerant of saltwater but more tolerant of cooler climates than the American crocodile, found only in tropical climates. American alligators are apex predators and consume fish, reptiles and mammals. Hatchlings feed on invertebrates, they play an important role as ecosystem engineers in wetland ecosystems through the creation of alligator holes, which provide both wet and dry habitats for other organisms.
Throughout the year, in particular during the breeding season, American alligators bellow to declare territory and locate suitable mates. Male American alligators use infrasound to attract females. Eggs are laid in a nest of vegetation, sticks and mud in a sheltered spot in or near the water. Young are born with yellow bands around their bodies and are protected by their mother for up to one year; the conservation status of the American alligator is listed as Least Concern by the International Union for Conservation of Nature. Hunting had decimated their population, the American alligator was listed as an endangered species by the Endangered Species Act of 1973. Subsequent conservation efforts have allowed their numbers to increase and the species was removed from endangered status in 1987. American alligators are now harvested for their skins and meat; the species is the official state reptile of three states: Florida and Mississippi. The American alligator was first classified by French zoologist François Marie Daudin as Crocodilus mississipiensis in 1801.
In 1807 Georges Cuvier created the genus Alligator. They are grouped in the family Alligatoridae with the caimans; the superfamily Alligatoroidea includes all crocodilians that are more related to the American alligator than to either the Nile crocodile or the gharial. Members of this superfamily first arose in about 100 -- 66 million years ago. Leidyosuchus of Alberta is the earliest known fossil, from the Campanian era 83 to 72 million years ago. Fossil alligatoroids have been found throughout Eurasia, because bridges across both the North Atlantic and the Bering Strait connected North America to Eurasia about 66 to 23 million years ago. Alligators and caimans split in North America during the late Cretaceous, the caimans reached South America by the Paleogene, before the closure of the Isthmus of Panama during the Neogene period, from about 23 to 2.58 million years ago. The Chinese alligator descended from a lineage that crossed the Bering land bridge during the Neogene. Fossils identical to the existing American alligator are found throughout the Pleistocene, from 2.5 million to 11.7 thousand years ago.
In 2016, a Miocene fossil skull of an alligator was found at Florida. Unlike the other extinct alligator species of in the same genus, the fossil skull was indistinguishable from that of the modern American alligator; this alligator and the American alligator are now considered to be sister taxa, meaning that the Alligator mississippiensis lineage has existed in North America for over 8 million years. The alligator's full mitochondrial genome was sequenced in the 1990s and it suggests the animal evolved at a rate similar to mammals and greater than birds and most cold-blooded vertebrates. However, the full genome, published in 2014, suggests that the alligator evolved much more than mammals and birds. Domestic American alligators range from long and slender to short and robust in response to variations in factors such as growth rate and climate; the American alligator is a large species of crocodilian. On average it is the second largest species in the family Alligatoridae, behind only the black caiman.
Weight varies depending on length, health and available food sources. Similar to many other reptiles that range expansively into temperate zones, American alligators from the northern end of their range, such as southern Arkansas and northern North Carolina, tend to reach smaller sizes. Large adult American alligators tend to be robust and bulky compared to other length crocodilians, for example captive males measuring 3 to 4 m were found to weigh 200 to 350 kg - although captive specimens may outweigh wild specimens due to lack of hunting behavior and other stressors; as with all crocodilians, as opposed to many mammals where size diminishes with old age, healthy American alligators may continue to expand throughout their lives and the oldest specimens are the largest. Old, large male American alligators reach an expected maximum size of up to 4.6 m in length, weighing up to 453 kg, while females reach a maximum of 3 m. On rare occasions, a large, old male may grow to an greater length. During the 19th and 20th centuries, larger males reaching 5 to 6 m (16 ft 5 in to 19 ft 8
The Chinese alligator known as the Yangtze alligator, China alligator, or the muddy dragon, is a critically endangered crocodilian endemic to China. It and the American alligator are the only living species in the genus Alligator of the family Alligatoridae. Dark gray or black in color with a armored body, the Chinese alligator grows to 1.5–2.1 metres in length and weighs 36–45 kilograms as an adult. It is nocturnal in summer. Mating occurs in early summer, with females most producing 20–30 eggs, which are smaller than those of any other crocodilian; the species is an opportunistic feeder eating fish and invertebrates. A vocal species, adults bellow during the mating season and young vocalize to communicate with their parents and other juveniles. Captive specimens have reached age 70, wild specimens can live to over 50. Living in bodies of fresh water, the Chinese alligator's range is restricted to six regions in the province of Anhui, as well as the provinces of Jiangsu and Zhejiang. Living as far away from its current range as Japan, the species had a wide range and population, but beginning in 5000 BC, multiple threats, such as habitat destruction, caused the species' population and range to decline.
The population in the wild was about 1000 in the 1970s, decreased to below 130 in 2001, grew after 2003, with its population being about 300 as of 2017. Listed as critically endangered by the International Union for Conservation of Nature, multiple conservation actions have been taking place for this species. Several breeding facilities, both in China and foreign countries, have bred specimens in captivity and sometimes released them back into the wild; the Chinese alligator has been a part of Chinese literature since the third century. In the late 1200s, Marco Polo became the first person outside of China to write about it. In some writings, the Chinese alligator has been associated with the Chinese dragon. Many pieces of evidence suggest that the Chinese alligator was the inspiration for the Chinese dragon. Chinese alligators have appeared in Chinese literature since 222–227 AD. Marco Polo was the first person outside of China to write about the alligator, when he came to China and discovered it in the late 1200s.
He said that the alligator lived in "caverns" in the day and hunted at night, that humans targeted its meat and skin, with its gall bladder having multiple medical purposes. He stated that it was found in lakes and springs in the province "Karazan". In 1656, Martino Martini, a priest, wrote that the Chinese alligator lived in the river Yangtze and was "much feared by the local residents". Unlike Polo, Martini wrote his description using information from Chinese literature. Chinese alligators were thought to give Buddhist priests merit if the priests were to buy alligators held in captivity and release them. In 1869, Robert Swinhoe saw a Chinese alligator in an exhibit in Shanghai and wrote the following year: In February, 1869, some Chinese were exhibiting in the native city of Shanghai what they called a dragon, which they declared had been dug out of a hole in the province of Shense, it was a young crocodile about four feet long. They made so much money by showing it. I can not, of course, guess its species.
The alligator was described by French naturalist Albert-Auguste Fauvel in 1879 as Alligator sinensis. The genus Alligator had contained only the American alligator since its creation in 1807. Fauvel wrote a detailed description of the species in a book titled Alligators in China: Their History, Description & Identification, including information about its historical account. In 1947, it was suggested to group the Chinese alligator in a separate genus from its American relative, due to the Chinese alligator's bony plate on its upper eyelid; this bony plate is present in caimans, but is present in the American alligator. At the time, the plate was thought to not appear in the American alligator at all; this produced the belief that the Chinese alligator's relationship with other crocodilians was between caimans and American alligators. Paulus Edward Pieris Deraniyagala described the genus Caigator the same year, which only contained the Chinese alligator, making its scientific name Caigator sinensis.
However, paleontology has shown that the Chinese alligator has evolved from other now-extinct members of the genus Alligator. This and the fact that the American alligator does infrequently have a bony plate on its eyelid have caused Caigator sinensis to now be classified as a synonym of Alligator sinensis. There is still not a consensus among biologists that the American and Chinese alligators belong to the same genus, despite multiple studies comparing the biochemistry and various other aspects of the two crocodilians; the genus, Alligator, is based on the Spanish word el lagarto, which translates to "the lizard". The specific name, sinensis, is from the Latin plural possessive sinaensis, meaning "belonging to China". One of the smallest species of crocodilians, the Chinese alligator attains a length of 1.5–2.1 metres and weight of 36–45 kilograms as an adult. Females are three-quarters the length of males, it is less than half the size of the American alligator, which grows to a length of 3.4 metres for males and 2.5 metres for females.
Reports are known of alligators in China reaching 3.0 metres in past centuries, but these are no longer thought to be accurate. The C
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most animals, allowing cells to be differentiated into specialised tissues and organs.
All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement, it first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm. In most cases, a third germ layer, the mesoderm develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
Louisiana is a state in the Deep South region of the South Central United States. It is the 25th most populous of the 50 United States. Louisiana is bordered by the state of Texas to the west, Arkansas to the north, Mississippi to the east, the Gulf of Mexico to the south. A large part of its eastern boundary is demarcated by the Mississippi River. Louisiana is the only U. S. state with political subdivisions termed parishes. The state's capital is Baton Rouge, its largest city is New Orleans. Much of the state's lands were formed from sediment washed down the Mississippi River, leaving enormous deltas and vast areas of coastal marsh and swamp; these contain a rich southern biota. There are many species of tree frogs, fish such as sturgeon and paddlefish. In more elevated areas, fire is a natural process in the landscape, has produced extensive areas of longleaf pine forest and wet savannas; these support an exceptionally large number of plant species, including many species of terrestrial orchids and carnivorous plants.
Louisiana has more Native American tribes than any other southern state, including four that are federally recognized, ten that are state recognized, four that have not received recognition. Some Louisiana urban environments have a multicultural, multilingual heritage, being so influenced by a mixture of 18th-century French, Spanish, Native American, African cultures that they are considered to be exceptional in the US. Before the American purchase of the territory in 1803, present-day Louisiana State had been both a French colony and for a brief period a Spanish one. In addition, colonists imported numerous African people as slaves in the 18th century. Many came from peoples of the same region of West Africa. In the post-Civil War environment, Anglo-Americans increased the pressure for Anglicization, in 1921, English was for a time made the sole language of instruction in Louisiana schools before a policy of multilingualism was revived in 1974. There has never been an official language in Louisiana, the state constitution enumerates "the right of the people to preserve and promote their respective historic and cultural origins."
Louisiana was named after Louis XIV, King of France from 1643 to 1715. When René-Robert Cavelier, Sieur de La Salle claimed the territory drained by the Mississippi River for France, he named it La Louisiane; the suffix -ana is a Latin suffix that can refer to "information relating to a particular individual, subject, or place." Thus Louis + ana carries the idea of "related to Louis." Once part of the French Colonial Empire, the Louisiana Territory stretched from present-day Mobile Bay to just north of the present-day Canada–United States border, including a small part of what is now the Canadian provinces of Alberta and Saskatchewan. The Gulf of Mexico did not exist 250 million years ago when there was but one supercontinent, Pangea; as Pangea split apart, the Atlantic Ocean and Gulf of Mexico opened. Louisiana developed, over millions of years, from water into land, from north to south; the oldest rocks are exposed in areas such as the Kisatchie National Forest. The oldest rocks date back to the early Cenozoic Era, some 60 million years ago.
The history of the formation of these rocks can be found in D. Spearing's Roadside Geology of Louisiana; the youngest parts of the state were formed during the last 12,000 years as successive deltas of the Mississippi River: the Maringouin, Teche, St. Bernard, the modern Mississippi, now the Atchafalaya; the sediments were carried from north to south by the Mississippi River. In between the Tertiary rocks of the north, the new sediments along the coast, is a vast belt known as the Pleistocene Terraces, their age and distribution can be related to the rise and fall of sea levels during past ice ages. In general, the northern terraces have had sufficient time for rivers to cut deep channels, while the newer terraces tend to be much flatter. Salt domes are found in Louisiana, their origin can be traced back to the early Gulf of Mexico, when the shallow ocean had high rates of evaporation. There are several hundred salt domes in the state. Salt domes are important not only as a source of salt. Louisiana is bordered to the west by Texas.
The state may properly be divided into two parts, the uplands of the north, the alluvial along the coast. The alluvial region includes low swamp lands, coastal marshlands and beaches, barrier islands that cover about 20,000 square miles; this area lies principally along the Gulf of Mexico and the Mississippi River, which traverses the state from north to south for a distance of about 600 mi ) and empties into the Gulf of Mexico. The breadth of the alluvial region along the Mississippi is from 10 to 60 miles, along the other rivers, the alluvial region averages about 10 miles across; the Mississippi River flows along a ridge formed by its own natural deposits, from which the lands decline toward a river beyond at an average fall of six feet per mile. The alluvial lands along other streams present similar features; the higher and contiguous hill lands of the north and northwestern part of the state have an area of more than 25,000 square miles. They consist of prairie and woodl
The Carboniferous is a geologic period and system that spans 60 million years from the end of the Devonian Period 358.9 million years ago, to the beginning of the Permian Period, 298.9 Mya. The name Carboniferous means "coal-bearing" and derives from the Latin words carbō and ferō, was coined by geologists William Conybeare and William Phillips in 1822. Based on a study of the British rock succession, it was the first of the modern'system' names to be employed, reflects the fact that many coal beds were formed globally during that time; the Carboniferous is treated in North America as two geological periods, the earlier Mississippian and the Pennsylvanian. Terrestrial animal life was well established by the Carboniferous period. Amphibians were the dominant land vertebrates, of which one branch would evolve into amniotes, the first terrestrial vertebrates. Arthropods were very common, many were much larger than those of today. Vast swaths of forest covered the land, which would be laid down and become the coal beds characteristic of the Carboniferous stratigraphy evident today.
The atmospheric content of oxygen reached its highest levels in geological history during the period, 35% compared with 21% today, allowing terrestrial invertebrates to evolve to great size. The half of the period experienced glaciations, low sea level, mountain building as the continents collided to form Pangaea. A minor marine and terrestrial extinction event, the Carboniferous rainforest collapse, occurred at the end of the period, caused by climate change. In the United States the Carboniferous is broken into Mississippian and Pennsylvanian subperiods; the Mississippian is about twice as long as the Pennsylvanian, but due to the large thickness of coal-bearing deposits with Pennsylvanian ages in Europe and North America, the two subperiods were long thought to have been more or less equal in duration. In Europe the Lower Carboniferous sub-system is known as the Dinantian, comprising the Tournaisian and Visean Series, dated at 362.5-332.9 Ma, the Upper Carboniferous sub-system is known as the Silesian, comprising the Namurian and Stephanian Series, dated at 332.9-298.9 Ma.
The Silesian is contemporaneous with the late Mississippian Serpukhovian plus the Pennsylvanian. In Britain the Dinantian is traditionally known as the Carboniferous Limestone, the Namurian as the Millstone Grit, the Westphalian as the Coal Measures and Pennant Sandstone; the International Commission on Stratigraphy faunal stages from youngest to oldest, together with some of their regional subdivisions, are: A global drop in sea level at the end of the Devonian reversed early in the Carboniferous. There was a drop in south polar temperatures; these conditions had little effect in the deep tropics, where lush swamps to become coal, flourished to within 30 degrees of the northernmost glaciers. Mid-Carboniferous, a drop in sea level precipitated a major marine extinction, one that hit crinoids and ammonites hard; this sea level drop and the associated unconformity in North America separate the Mississippian subperiod from the Pennsylvanian subperiod. This happened about 323 million years ago, at the onset of the Permo-Carboniferous Glaciation.
The Carboniferous was a time of active mountain-building as the supercontinent Pangaea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America–Europe along the present line of eastern North America; this continental collision resulted in the Hercynian orogeny in Europe, the Alleghenian orogeny in North America. In the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural Mountains. Most of the Mesozoic supercontinent of Pangea was now assembled, although North China, South China continents were still separated from Laurasia; the Late Carboniferous Pangaea was shaped like an "O." There were two major oceans in the Carboniferous—Panthalassa and Paleo-Tethys, inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and closed - Rheic Ocean, the small, shallow Ural Ocean and Proto-Tethys Ocean. Average global temperatures in the Early Carboniferous Period were high: 20 °C.
However, cooling during the Middle Carboniferous reduced average global temperatures to about 12 °C. Lack of growth rings of fossilized trees suggest a lack of seasons of a tropical climate. Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are referred to as Permo-Carboniferous in age; the cooling and drying of the climate led to the Carboniferous Rainforest Collapse during the late Carboniferous. Tropical rainforests fragmented and were devastated by climate change. Carboniferous rocks in Europe and eastern North America consist of a repeated sequence of limestone, sandstone and coal beds. In North America, the early Carboniferous is marine