Agadez Region is one of the seven regions of Niger . At 667,799 square kilometres (257,839 sq mi), it covers more than half of Niger's land area, and is the largest region in the country, as well as the largest African state subdivision . The capital of the department is Agadez .
90-533: The region is a centre for palaeontology , with numerous dinosaur skeletons being found here, including the Ouranosaurus nigeriensis . Cave painting and the remains of ancient human settlements are also located here. Tuareg peoples began migrating to the region from the mid-8th century. From the mid-15th century to the early 20th, much of the region was under the control of the Sultanate of Agadez , except for
180-471: A jigsaw puzzle . Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil's age must lie between the two known ages. Because rock sequences are not continuous, but may be broken up by faults or periods of erosion , it is very difficult to match up rock beds that are not directly next to one another. However, fossils of species that survived for
270-552: A collision that formed the Moon about 40 million years later, may have cooled quickly enough to have oceans and an atmosphere about 4,440 million years ago . There is evidence on the Moon of a Late Heavy Bombardment by asteroids from 4,000 to 3,800 million years ago . If, as seems likely, such a bombardment struck Earth at the same time, the first atmosphere and oceans may have been stripped away. Paleontology traces
360-602: A common ancestor. Ideally the "family tree" has only two branches leading from each node ("junction"), but sometimes there is too little information to achieve this, and paleontologists have to make do with junctions that have several branches. The cladistic technique is sometimes fallible, as some features, such as wings or camera eyes , evolved more than once, convergently – this must be taken into account in analyses. Evolutionary developmental biology , commonly abbreviated to "Evo Devo", also helps paleontologists to produce "family trees", and understand fossils. For example,
450-456: A constant rate. These " molecular clocks ", however, are fallible, and provide only a very approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, and estimates produced by different techniques may vary by a factor of two. Earth formed about 4,570 million years ago and, after
540-576: A country's development status. They conclude that 11%, 21% and 34% of all countries can be interpreted as currently misclassified in the development bins due to the three sources of data error, respectively. Wolff, Chong and Auffhammer suggest that the United Nations should discontinue the practice of classifying countries into development bins because the cut-off values seem arbitrary, and the classifications can provide incentives for strategic behavior in reporting official statistics, as well as having
630-403: A data source that is not limited to animals with easily fossilised hard parts, and they reflect organisms' behaviours. Also many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them. Whilst exact assignment of trace fossils to their makers is generally impossible, traces may for example provide the earliest physical evidence of
720-573: A fortunate accident during other research. For example, the 1980 discovery by Luis and Walter Alvarez of iridium , a mainly extraterrestrial metal, in the Cretaceous – Paleogene boundary layer made asteroid impact the most favored explanation for the Cretaceous–Paleogene extinction event – although debate continues about the contribution of volcanism. A complementary approach to developing scientific knowledge, experimental science ,
810-821: A minor group until the first jawed fish appeared in the Late Ordovician . The spread of animals and plants from water to land required organisms to solve several problems, including protection against drying out and supporting themselves against gravity . The earliest evidence of land plants and land invertebrates date back to about 476 million years ago and 490 million years ago respectively. Those invertebrates, as indicated by their trace and body fossils, were shown to be arthropods known as euthycarcinoids . The lineage that produced land vertebrates evolved later but very rapidly between 370 million years ago and 360 million years ago ; recent discoveries have overturned earlier ideas about
900-530: A number of grounds, including focusing exclusively on national performance and ranking, lack of attention to development from a global perspective, measurement error of the underlying statistics, and on the UNDP's changes in formula which can lead to severe misclassification of "low", "medium", "high" or "very high" human development countries. There have also been various criticism towards the lack of consideration regarding sustainability (which later got addressed by
990-569: A period when the area came under the rule of the Songhai Empire in the 1500s. The region suffered with the advent of French colonialism as power shifted away to the southwest; Tuareg disaffection with French rule resulted in the Kaocen revolt in 1916–17. This process continued following Niger's independence in 1960; local Tuareg saw little recompense from the uranium mining boom in Arlit in
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#17327655664981080-555: A rapid increase in knowledge about the history of life on Earth and to progress in the definition of the geologic time scale , largely based on fossil evidence. Although she was rarely recognised by the scientific community, Mary Anning was a significant contributor to the field of palaeontology during this period; she uncovered multiple novel Mesozoic reptile fossils and deducted that what were then known as bezoar stones are in fact fossilised faeces . In 1822 Henri Marie Ducrotay de Blainville , editor of Journal de Physique , coined
1170-543: A relatively short time can be used to link up isolated rocks: this technique is called biostratigraphy . For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period. If rocks of unknown age are found to have traces of E. pseudoplanus , they must have a mid-Ordovician age. Such index fossils must be distinctive, be globally distributed and have a short time range to be useful. However, misleading results are produced if
1260-608: A steady increase in brain size after about 3 million years ago . There is a long-running debate about whether modern humans are descendants of a single small population in Africa , which then migrated all over the world less than 200,000 years ago and replaced previous hominine species, or arose worldwide at the same time as a result of interbreeding . Life on earth has suffered occasional mass extinctions at least since 542 million years ago . Despite their disastrous effects, mass extinctions have sometimes accelerated
1350-435: Is a statistical composite index of life expectancy , education (mean years of schooling completed and expected years of schooling upon entering the education system ), and per capita income indicators, which is used to rank countries into four tiers of human development . A country scores a higher level of HDI when the lifespan is higher, the education level is higher, and the gross national income GNI (PPP) per capita
1440-595: Is composed only of eukaryotic cells, and the earliest evidence for it is the Francevillian Group Fossils from 2,100 million years ago , although specialisation of cells for different functions first appears between 1,430 million years ago (a possible fungus) and 1,200 million years ago (a probable red alga ). Sexual reproduction may be a prerequisite for specialisation of cells, as an asexual multicellular organism might be at risk of being taken over by rogue cells that retain
1530-412: Is considered central — someone choosing to be hungry (e.g. when fasting for religious reasons ) is considered different from someone who is hungry because they cannot afford to buy food, or because the country is going through a famine . The index does not take into account several factors, such as the net wealth per capita or the relative quality of goods in a country. This situation tends to lower
1620-482: Is hard to decide at what level to place a new higher-level grouping, e.g. genus or family or order ; this is important since the Linnaean rules for naming groups are tied to their levels, and hence if a group is moved to a different level it must be renamed. Paleontologists generally use approaches based on cladistics , a technique for working out the evolutionary "family tree" of a set of organisms. It works by
1710-608: Is higher. It was developed by Pakistani economist Mahbub ul-Haq and was further used to measure a country's development by the United Nations Development Programme (UNDP)'s Human Development Report Office. The 2010 Human Development Report introduced an inequality-adjusted Human Development Index (IHDI). While the simple HDI remains useful, it stated that "the IHDI is the actual level of human development (accounting for this inequality ), while
1800-443: Is often said to work by conducting experiments to disprove hypotheses about the workings and causes of natural phenomena. This approach cannot prove a hypothesis, since some later experiment may disprove it, but the accumulation of failures to disprove is often compelling evidence in favor. However, when confronted with totally unexpected phenomena, such as the first evidence for invisible radiation , experimental scientists often use
1890-594: Is one that contained an extinct "crocodile-like" marine reptile, which eventually came to be known as the mosasaurid Mosasaurus of the Cretaceous period. The first half of the 19th century saw geological and paleontological activity become increasingly well organised with the growth of geologic societies and museums and an increasing number of professional geologists and fossil specialists. Interest increased for reasons that were not purely scientific, as geology and paleontology helped industrialists to find and exploit natural resources such as coal. This contributed to
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#17327655664981980-401: Is our only means of giving rocks greater than about 50 million years old an absolute age, and can be accurate to within 0.5% or better. Although radiometric dating requires very careful laboratory work, its basic principle is simple: the rates at which various radioactive elements decay are known, and so the ratio of the radioactive element to the element into which it decays shows how long ago
2070-506: Is sparsely populated. Its 487,620 inhabitants (as per the 2012 census) account for only 2.8% of the total population of Niger, with a population density of 0.73 inhabitants per square kilometre (1.9/sq mi). Much of its population comprises nomadic or semi-nomadic peoples, including Arabs , Fulani , Kanuri , Dazaga Toubou and various Tuareg groups. The Tagdal language and Tasawaq language , thought to be mixed Songhai -Tuareg languages, are also spoken. Traversed for centuries by
2160-666: Is the year when the report was published. The HDI has extended its geographical coverage: David Hastings, of the United Nations Economic and Social Commission for Asia and the Pacific , published a report geographically extending the HDI to 230+ economies, whereas the UNDP HDI for 2009 enumerates 182 economies and coverage for the 2010 HDI dropped to 169 countries. The Human Development Index has been criticized on
2250-503: Is thought to have been propelled by coevolution with pollinating insects. Social insects appeared around the same time and, although they account for only small parts of the insect "family tree", now form over 50% of the total mass of all insects. Humans evolved from a lineage of upright-walking apes whose earliest fossils date from over 6 million years ago . Although early members of this lineage had chimp -sized brains, about 25% as big as modern humans', there are signs of
2340-582: The Middle Ages the Persian naturalist Ibn Sina , known as Avicenna in Europe, discussed fossils and proposed a theory of petrifying fluids on which Albert of Saxony elaborated in the 14th century. The Chinese naturalist Shen Kuo (1031–1095) proposed a theory of climate change based on the presence of petrified bamboo in regions that in his time were too dry for bamboo. In early modern Europe ,
2430-538: The Neogene - Quaternary . In deeper-level deposits in western Europe are early-aged mammals such as the palaeothere perissodactyl Palaeotherium and the anoplotheriid artiodactyl Anoplotherium , both of which were described earliest after the former two genera, which today are known to date to the Paleogene period. Cuvier figured out that even older than the two levels of deposits with extinct large mammals
2520-637: The Permian–Triassic extinction event . Amphibians Extinct Synapsids Mammals Extinct reptiles Lizards and snakes Extinct Archosaurs Crocodilians Extinct Dinosaurs Birds Naming groups of organisms in a way that is clear and widely agreed is important, as some disputes in paleontology have been based just on misunderstandings over names. Linnaean taxonomy is commonly used for classifying living organisms, but runs into difficulties when dealing with newly discovered organisms that are significantly different from known ones. For example: it
2610-516: The Permian–Triassic extinction event . A relatively recent discipline, molecular phylogenetics , compares the DNA and RNA of modern organisms to re-construct the "family trees" of their evolutionary ancestors. It has also been used to estimate the dates of important evolutionary developments, although this approach is controversial because of doubts about the reliability of the " molecular clock ". Techniques from engineering have been used to analyse how
2700-530: The Trans-Saharan trade routes, the oasis towns of the Aïr and the eastern Kaouar Cliffs are known for their gardens, salt manufacture, and date cultivation. Arlit is the centre of Niger's uranium industry, a prominent economic sector in the region with uranium pits and mines operated by foreign companies providing substantial revenue for the country. The French discovered Niger's first uranium deposits in
2790-454: The embryological development of some modern brachiopods suggests that brachiopods may be descendants of the halkieriids , which became extinct in the Cambrian period. Paleontology seeks to map out how living things have changed through time. A substantial hurdle to this aim is the difficulty of working out how old fossils are. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating . This technique
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2880-481: The lowest and highest values the variable x {\displaystyle x} can attain, respectively. The Human Development Index (HDI) then represents the uniformly weighted sum with 1 ⁄ 3 contributed by each of the following factor indices: The Human Development Report 2023/24 by the United Nations Development Programme was released on 13 March 2024; the report calculates HDI values based on data collected in 2022. Ranked from 1 to 69 in
2970-488: The planetary pressures-adjusted HDI ), social inequality (which got addressed by the inequality-adjusted HDI ), unemployment or democracy . Economists Hendrik Wolff, Howard Chong and Maximilian Auffhammer discuss the HDI from the perspective of data error in the underlying health, education and income statistics used to construct the HDI. They have identified three sources of data error which are: (i) data updating, (ii) formula revisions and (iii) thresholds to classify
3060-526: The " jigsaw puzzles " of biostratigraphy (arrangement of rock layers from youngest to oldest). Classifying ancient organisms is also difficult, as many do not fit well into the Linnaean taxonomy classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of molecular phylogenetics , which investigates how closely organisms are related by measuring
3150-472: The 1970s, and Agadez Region was struck by repeated droughts and famines. Since then there have been two Tuareg rebellions: from 1990–95 and 2007–09 . In recent years the region has also been affected by an insurgency in the Maghreb by Islamist groups. The Agadez Region borders Algeria ( Tamanrasset Province and Illizi Province ) and Libya ( Murzuq District ) to the north, Chad ( Tibesti Region ) to
3240-1222: The 2010 Human Development Report calculated the HDI combining three dimensions: In its 2010 Human Development Report, the UNDP began using a new method of calculating the HDI. The following three indices are used: 1. Life Expectancy Index (LEI) = LE − 20 85 − 20 = LE − 20 65 {\displaystyle ={\frac {{\textrm {LE}}-20}{85-20}}={\frac {{\textrm {LE}}-20}{65}}} 2. Education Index (EI) = MYSI + EYSI 2 {\displaystyle ={\frac {{\textrm {MYSI}}+{\textrm {EYSI}}}{2}}} 3. Income Index (II) = ln ( GNIpc ) − ln ( 100 ) ln ( 75 , 000 ) − ln ( 100 ) = ln ( GNIpc ) − ln ( 100 ) ln ( 750 ) {\displaystyle ={\frac {\ln({\textrm {GNIpc}})-\ln(100)}{\ln(75,000)-\ln(100)}}={\frac {\ln({\textrm {GNIpc}})-\ln(100)}{\ln(750)}}} Finally,
3330-555: The Early Cambrian , along with several "weird wonders" that bear little obvious resemblance to any modern animals. There is a long-running debate about whether this Cambrian explosion was truly a very rapid period of evolutionary experimentation; alternative views are that modern-looking animals began evolving earlier but fossils of their precursors have not yet been found, or that the "weird wonders" are evolutionary "aunts" and "cousins" of modern groups. Vertebrates remained
3420-463: The Earth's organic and inorganic past". William Whewell (1794–1866) classified paleontology as one of the historical sciences, along with archaeology , geology, astronomy , cosmology , philology and history itself: paleontology aims to describe phenomena of the past and to reconstruct their causes. Hence it has three main elements: description of past phenomena; developing a general theory about
3510-591: The HDI can be viewed as an index of 'potential' human development (or the maximum level of HDI) that could be achieved if there was no inequality." The index is based on the human development approach, developed by Mahbub ul-Haq, anchored in Amartya Sen 's work on human capabilities, and often framed in terms of whether people are able to "be" and "do" desirable things in life. Examples include — being: well-fed, sheltered, and healthy; doing: work, education, voting, participating in community life. The freedom of choice
3600-522: The HDI is the geometric mean of the previous three normalized indices: LE: Life expectancy at birth MYS: Mean years of schooling (i.e. years that a person aged 25 or older has spent in formal education) EYS: Expected years of schooling (i.e. total expected years of schooling for children under 18 years of age, incl. young men and women aged 13–17) GNIpc: Gross national income at purchasing power parity per capita The HDI combined three dimensions last used in its 2009 report: This methodology
3690-546: The Tim Mersoi Basin of the Agadez Region in 1958 and since then French companies such as Areva have maintained a large footprint in the region, employing a large quantity of locals. Depressed uranium prices since the 1980s have hit the region hard, though uranium remains one of the main foreign exchange earners for the country and a main export. The region is less poor than other regions of the country. It has
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3780-499: The Wolff et al. paper. The Human Development Report Office states that they undertook a systematic revision of the methods used for the calculation of the HDI, and that the new methodology directly addresses the critique by Wolff et al. in that it generates a system for continuously updating the human-development categories whenever formula or data revisions take place. In 2013, Salvatore Monni and Alessandro Spaventa emphasized that in
3870-412: The ability to reproduce. The earliest known animals are cnidarians from about 580 million years ago , but these are so modern-looking that they must be descendants of earlier animals. Early fossils of animals are rare because they had not developed mineralised , easily fossilized hard parts until about 548 million years ago . The earliest modern-looking bilaterian animals appear in
3960-515: The appearance of moderately complex animals (comparable to earthworms ). Geochemical observations may help to deduce the global level of biological activity at a certain period, or the affinity of certain fossils. For example, geochemical features of rocks may reveal when life first arose on Earth, and may provide evidence of the presence of eukaryotic cells, the type from which all multicellular organisms are built. Analyses of carbon isotope ratios may help to explain major transitions such as
4050-625: The atmosphere increased their effectiveness as nurseries of evolution. While eukaryotes , cells with complex internal structures, may have been present earlier, their evolution speeded up when they acquired the ability to transform oxygen from a poison to a powerful source of metabolic energy. This innovation may have come from primitive eukaryotes capturing oxygen-powered bacteria as endosymbionts and transforming them into organelles called mitochondria . The earliest evidence of complex eukaryotes with organelles (such as mitochondria) dates from 1,850 million years ago . Multicellular life
4140-415: The bodies of ancient organisms might have worked, for example the running speed and bite strength of Tyrannosaurus , or the flight mechanics of Microraptor . It is relatively commonplace to study the internal details of fossils using X-ray microtomography . Paleontology, biology, archaeology, and paleoneurobiology combine to study endocranial casts (endocasts) of species related to humans to clarify
4230-729: The border between biology and geology , but it differs from archaeology in that it excludes the study of anatomically modern humans . It now uses techniques drawn from a wide range of sciences, including biochemistry , mathematics , and engineering. Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life , almost back to when Earth became capable of supporting life, nearly 4 billion years ago. As knowledge has increased, paleontology has developed specialised sub-divisions, some of which focus on different types of fossil organisms while others study ecology and environmental history, such as ancient climates . Body fossils and trace fossils are
4320-401: The causes of various types of change; and applying those theories to specific facts. When trying to explain the past, paleontologists and other historical scientists often construct a set of one or more hypotheses about the causes and then look for a " smoking gun ", a piece of evidence that strongly accords with one hypothesis over any others. Sometimes researchers discover a "smoking gun" by
4410-763: The characteristics and evolution of humans as a species. When dealing with evidence about humans, archaeologists and paleontologists may work together – for example paleontologists might identify animal or plant fossils around an archaeological site , to discover the people who lived there, and what they ate; or they might analyze the climate at the time of habitation. In addition, paleontology often borrows techniques from other sciences, including biology, osteology , ecology, chemistry , physics and mathematics. For example, geochemical signatures from rocks may help to discover when life first arose on Earth, and analyses of carbon isotope ratios may help to identify climate changes and even to explain major transitions such as
4500-520: The chronological order in which rocks were formed, is useful to both paleontologists and geologists. Biogeography studies the spatial distribution of organisms, and is also linked to geology, which explains how Earth's geography has changed over time. Although paleontology became established around 1800, earlier thinkers had noticed aspects of the fossil record. The ancient Greek philosopher Xenophanes (570–480 BCE) concluded from fossil sea shells that some areas of land were once under water. During
4590-445: The date when lineages first appeared. For instance, if fossils of B or C date to X million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved more than X million years ago. It is also possible to estimate how long ago two living clades diverged – i.e. approximately how long ago their last common ancestor must have lived – by assuming that DNA mutations accumulate at
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#17327655664984680-594: The development of mammalian traits such as endothermy and hair. After the Cretaceous–Paleogene extinction event 66 million years ago killed off all the dinosaurs except the birds, mammals increased rapidly in size and diversity, and some took to the air and the sea. Fossil evidence indicates that flowering plants appeared and rapidly diversified in the Early Cretaceous between 130 million years ago and 90 million years ago . Their rapid rise to dominance of terrestrial ecosystems
4770-561: The development of the body plans of most animal phyla . The discovery of fossils of the Ediacaran biota and developments in paleobiology extended knowledge about the history of life back far before the Cambrian. Increasing awareness of Gregor Mendel 's pioneering work in genetics led first to the development of population genetics and then in the mid-20th century to the modern evolutionary synthesis , which explains evolution as
4860-482: The different levels of deposits represented different time periods in the early 19th century. The surface-level deposits in the Americas contained later mammals like the megatheriid ground sloth Megatherium and the mammutid proboscidean Mammut (later known informally as a "mastodon"), which were some of the earliest-named fossil mammal genera with official taxonomic authorities. They today are known to date to
4950-499: The east, Diffa Region , Zinder Region , Tahoua Region and Maradi Region to the south, and Mali ( Kidal Region ) to the west. It is by far the largest region of the country, representing 52% of the total area of Niger. The region is dominated by the Sahara desert , and includes the vast Ténéré portion of that desert, as well as dune seas such as the Erg of Bilma . The Aïr Mountains ,
5040-409: The end of the 20th century have been particularly important as they have provided new information about the earliest evolution of animals, early fish, dinosaurs and the evolution of birds. The last few decades of the 20th century saw a renewed interest in mass extinctions and their role in the evolution of life on Earth. There was also a renewed interest in the Cambrian explosion that apparently saw
5130-453: The evolution of life on earth. When dominance of an ecological niche passes from one group of organisms to another, this is rarely because the new dominant group outcompetes the old, but usually because an extinction event allows a new group, which may possess an advantageous trait, to outlive the old and move into its niche. Human Development Index This is an accepted version of this page The Human Development Index ( HDI )
5220-410: The evolution of the human brain. Paleontology even contributes to astrobiology , the investigation of possible life on other planets , by developing models of how life may have arisen and by providing techniques for detecting evidence of life. As knowledge has increased, paleontology has developed specialised subdivisions. Vertebrate paleontology concentrates on fossils from the earliest fish to
5310-466: The evolutionary history of life back to over 3,000 million years ago , possibly as far as 3,800 million years ago . The oldest clear evidence of life on Earth dates to 3,000 million years ago , although there have been reports, often disputed, of fossil bacteria from 3,400 million years ago and of geochemical evidence for the presence of life 3,800 million years ago . Some scientists have proposed that life on Earth
5400-555: The exceptional events that cause quick burial make it difficult to study the normal environments of the animals. The sparseness of the fossil record means that organisms are expected to exist long before and after they are found in the fossil record – this is known as the Signor–Lipps effect . Trace fossils consist mainly of tracks and burrows, but also include coprolites (fossil feces ) and marks left by feeding. Trace fossils are particularly significant because they represent
5490-416: The focus of development economics from national income accounting to people-centered policies ". He believed that a simple composite measure of human development was needed to convince the public, academics and politicians that they can, and should, evaluate development not only by economic advances but also improvements in human well-being . Published on 4 November 2010 (and updated on 10 June 2011),
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#17327655664985580-515: The focus of paleontology shifted to understanding evolutionary paths, including human evolution , and evolutionary theory. The last half of the 19th century saw a tremendous expansion in paleontological activity, especially in North America. The trend continued in the 20th century with additional regions of the Earth being opened to systematic fossil collection. Fossils found in China near
5670-449: The following: At the end of the 18th century Georges Cuvier 's work established comparative anatomy as a scientific discipline and, by proving that some fossil animals resembled no living ones, demonstrated that animals could become extinct , leading to the emergence of paleontology. The expanding knowledge of the fossil record also played an increasing role in the development of geology, particularly stratigraphy . Cuvier proved that
5760-580: The fossil record: different environments are more favorable to the preservation of different types of organism or parts of organisms. Further, only the parts of organisms that were already mineralised are usually preserved, such as the shells of molluscs. Since most animal species are soft-bodied, they decay before they can become fossilised. As a result, although there are 30-plus phyla of living animals, two-thirds have never been found as fossils. Occasionally, unusual environments may preserve soft tissues. These lagerstätten allow paleontologists to examine
5850-687: The history and driving forces behind their evolution. Land plants were so successful that their detritus caused an ecological crisis in the Late Devonian , until the evolution of fungi that could digest dead wood. During the Permian period, synapsids , including the ancestors of mammals , may have dominated land environments, but this ended with the Permian–Triassic extinction event 251 million years ago , which came very close to wiping out all complex life. The extinctions were apparently fairly sudden, at least among vertebrates. During
5940-533: The history of Earth's climate and the mechanisms that have changed it – which have sometimes included evolutionary developments, for example the rapid expansion of land plants in the Devonian period removed more carbon dioxide from the atmosphere, reducing the greenhouse effect and thus helping to cause an ice age in the Carboniferous period. Biostratigraphy , the use of fossils to work out
6030-542: The immediate ancestors of modern mammals . Invertebrate paleontology deals with fossils such as molluscs , arthropods , annelid worms and echinoderms . Paleobotany studies fossil plants , algae , and fungi. Palynology , the study of pollen and spores produced by land plants and protists , straddles paleontology and botany , as it deals with both living and fossil organisms. Micropaleontology deals with microscopic fossil organisms of all kinds. Instead of focusing on individual organisms, paleoecology examines
6120-434: The index fossils turn out to have longer fossil ranges than first thought. Stratigraphy and biostratigraphy can in general provide only relative dating ( A was before B ), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of the problems involved in matching up rocks of the same age across different continents . Family-tree relationships may also help to narrow down
6210-538: The interactions between different ancient organisms, such as their food chains , and the two-way interactions with their environments. For example, the development of oxygenic photosynthesis by bacteria caused the oxygenation of the atmosphere and hugely increased the productivity and diversity of ecosystems . Together, these led to the evolution of complex eukaryotic cells, from which all multicellular organisms are built. Paleoclimatology , although sometimes treated as part of paleoecology, focuses more on
6300-463: The internal anatomy of animals that in other sediments are represented only by shells, spines, claws, etc. – if they are preserved at all. However, even lagerstätten present an incomplete picture of life at the time. The majority of organisms living at the time are probably not represented because lagerstätten are restricted to a narrow range of environments, e.g. where soft-bodied organisms can be preserved very quickly by events such as mudslides; and
6390-456: The investigation of evolutionary "family trees" by techniques derived from biochemistry , began to make an impact, particularly when it was proposed that the human lineage had diverged from apes much more recently than was generally thought at the time. Although this early study compared proteins from apes and humans, most molecular phylogenetics research is now based on comparisons of RNA and DNA . Fossils of organisms' bodies are usually
6480-409: The logic that, if groups B and C have more similarities to each other than either has to group A, then B and C are more closely related to each other than either is to A. Characters that are compared may be anatomical , such as the presence of a notochord , or molecular , by comparing sequences of DNA or proteins . The result of a successful analysis is a hierarchy of clades – groups that share
6570-409: The most informative type of evidence. The most common types are wood, bones, and shells. Fossilisation is a rare event, and most fossils are destroyed by erosion or metamorphism before they can be observed. Hence the fossil record is very incomplete, increasingly so further back in time. Despite this, it is often adequate to illustrate the broader patterns of life's history. There are also biases in
6660-524: The numbers of tourists, with most third party governments advising against travel to the region. Palaeontology Paleontology ( / ˌ p eɪ l i ɒ n ˈ t ɒ l ə dʒ i , ˌ p æ l i -, - ən -/ PAY -lee-on- TOL -ə-jee, PAL -ee-, -ən- ), also spelled palaeontology or palæontology , is the scientific study of life that existed prior to the start of the Holocene epoch (roughly 11,700 years before present). It includes
6750-414: The outcome of events such as mutations and horizontal gene transfer , which provide genetic variation , with genetic drift and natural selection driving changes in this variation over time. Within the next few years the role and operation of DNA in genetic inheritance were discovered, leading to what is now known as the "Central Dogma" of molecular biology . In the 1960s molecular phylogenetics ,
6840-523: The potential to misguide politicians, investors, charity donors and the public who use the HDI at large. In 2010, the UNDP reacted to the criticism by updating the thresholds to classify nations as low, medium, and high human development countries. In a comment to The Economist in early January 2011, the Human Development Report Office responded to an article published in the magazine on 6 January 2011 which discusses
6930-452: The principal types of evidence about ancient life, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave body fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating , which provides absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving
7020-432: The radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are a few volcanic ash layers. Consequently, paleontologists must usually rely on stratigraphy to date fossils. Stratigraphy is the science of deciphering the "layer-cake" that is the sedimentary record, and has been compared to
7110-450: The ranking of some of the most developed countries , such as the G7 members and others. The origins of the HDI are found in the annual Human Development Reports produced by the Human Development Report Office of the United Nations Development Programme (UNDP). These annual reports were devised and launched by Pakistani economist Mahbub ul-Haq in 1990, and had the explicit purpose "to shift
7200-701: The same approach as historical scientists: construct a set of hypotheses about the causes and then look for a "smoking gun". Paleontology lies between biology and geology since it focuses on the record of past life, but its main source of evidence is fossils in rocks. For historical reasons, paleontology is part of the geology department at many universities: in the 19th and early 20th centuries, geology departments found fossil evidence important for dating rocks, while biology departments showed little interest. Paleontology also has some overlap with archaeology , which primarily works with objects made by humans and with human remains, while paleontologists are interested in
7290-576: The second-highest Human Development Index and the second-lowest incidence of extreme poverty according to World Bank data from 2018. Agadez had historically been one of the main centres of tourism in Niger, with visitors attracted by the desert scenery, archaeological sites and the Air Mountains. However Tuareg rebellions and activities of Islamist militants in Agadez region have severely reduced
7380-478: The similarity of the DNA in their genomes . Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend. The simplest definition of "paleontology" is "the study of ancient life". The field seeks information about several aspects of past organisms: "their identity and origin, their environment and evolution, and what they can tell us about
7470-470: The slow recovery from this catastrophe a previously obscure group, archosaurs , became the most abundant and diverse terrestrial vertebrates. One archosaur group, the dinosaurs, were the dominant land vertebrates for the rest of the Mesozoic , and birds evolved from one group of dinosaurs. During this time mammals' ancestors survived only as small, mainly nocturnal insectivores , which may have accelerated
7560-625: The study of fossils to classify organisms and study their interactions with each other and their environments (their paleoecology ). Paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuvier 's work on comparative anatomy , and developed rapidly in the 19th century. The term has been used since 1822 formed from Greek παλαιός ( 'palaios' , "old, ancient"), ὄν ( 'on' , ( gen. 'ontos' ), "being, creature"), and λόγος ( 'logos' , "speech, thought, study"). Paleontology lies on
7650-629: The systematic study of fossils emerged as an integral part of the changes in natural philosophy that occurred during the Age of Reason . In the Italian Renaissance, Leonardo da Vinci made various significant contributions to the field as well as depicted numerous fossils. Leonardo's contributions are central to the history of paleontology because he established a line of continuity between the two main branches of paleontology – ichnology and body fossil paleontology. He identified
7740-400: The tallest peaks in Niger, are also located here. The Djado Plateau is located in the far north. Agadez is the regional capital; other major settlements include Aderbissinat , Arlit , Assamakka , Bilma , Dirkou , Iferouane , In-Gall , Madama , Séguedine , Tchirozerine , Tegguiada In Tessoum and Timia . Agadez is subdivided into six departments Agadez has a large area but
7830-406: The word "palaeontology" to refer to the study of ancient living organisms through fossils. As knowledge of life's history continued to improve, it became increasingly obvious that there had been some kind of successive order to the development of life. This encouraged early evolutionary theories on the transmutation of species . After Charles Darwin published Origin of Species in 1859, much of
7920-503: The year 2022, the following countries are considered to be of "very high human development": The list below displays the top-ranked country from each year of the Human Development Index. Norway has been ranked the highest sixteen times, Canada eight times, and Switzerland, Japan, and Iceland have each ranked twice. The year represents the time period from which the statistics for the index were derived. In parentheses
8010-454: Was "seeded" from elsewhere , but most research concentrates on various explanations of how life could have arisen independently on Earth. For about 2,000 million years microbial mats , multi-layered colonies of different bacteria, were the dominant life on Earth. The evolution of oxygenic photosynthesis enabled them to play the major role in the oxygenation of the atmosphere from about 2,400 million years ago . This change in
8100-570: Was used by the UNDP until their 2011 report. The formula defining the HDI is promulgated by the United Nations Development Programme ( UNDP ). In general, to transform a raw variable , say x {\displaystyle x} , into a unit-free index between 0 and 1 (which allows different indices to be added together), the following formula is used: where a {\displaystyle a} and b {\displaystyle b} are
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