Ab urbe condita
Ab urbe condita, or Anno urbis conditæ abbreviated as AUC in either case, is a convention, used in antiquity and by classical historians to refer to a given year in Ancient Rome. Ab urbe condita means "from the founding of the City," while anno urbis conditæ means "in the year since the City's founding." Therefore, the traditional year of the foundation of Rome, 753 BC, would be written AUC 1, while AD 1 would be AUC 754. The foundation of the Empire in 27 BC would be AUC 727. Usage of the term was more common during the Renaissance, when editors sometimes added AUC to Roman manuscripts they published, giving the false impression that the convention was used in antiquity. In reality, the dominant method of identifying years in Roman times was to name the two consuls who held office that year. In late antiquity, regnal years were in use, as was the Diocletian era in Roman Egypt after AD 293, in the Byzantine Empire after AD 537, following a decree by Justinian; the traditional date for the founding of Rome, 21 April 753 BC, is due to Marcus Terentius Varro.
Varro may have used the consular list and called the year of the first consuls "ab urbe condita 245," accepting the 244-year interval from Dionysius of Halicarnassus for the kings after the foundation of Rome. The correctness of this calculation has not been confirmed. From the time of Claudius onward, this calculation superseded other contemporary calculations. Celebrating the anniversary of the city became part of imperial propaganda. Claudius was the first to hold magnificent celebrations in honor of the anniversary of the city, in AD 48, the eight hundredth year from the founding of the city. Hadrian and Antoninus Pius held similar celebrations, in AD 121, in AD 147 and AD 148, respectively. In AD 248, Philip the Arab celebrated Rome's first millennium, together with Ludi saeculares for Rome's alleged tenth sæculum. Coins from his reign commemorate the celebrations. A coin by a contender for the imperial throne, explicitly states "ear one thousand and first", an indication that the citizens of the empire had a sense of the beginning of a new era, a Sæculum Novum.
The Anno Domini year numbering was developed by a monk named Dionysius Exiguus in Rome in AD 525, as a result of his work on calculating the date of Easter. Dionysius did not use the AUC convention, but instead based his calculations on the Diocletian era; this convention had been in use since AD 293, the year of the tetrarchy, as it became impractical to use regnal years of the current emperor. In his Easter table, the year AD 532 was equated with the 248th regnal year of Diocletian; the table counted the years starting from the presumed birth of Christ, rather than the accession of the emperor Diocletian on 20 November AD 284, or as stated by Dionysius: "sed magis elegimus ab incarnatione Domini nostri Jesu Christi annorum tempora praenotare". Blackburn and Holford-Strevens review interpretations of Dionysius which place the Incarnation in 2 BC, 1 BC, or AD 1, it has been calculated that the year AD 1 corresponds to AUC 754, based on the epoch of Varro. Thus, AUC 1 = 753 BC AUC 753 = 1 BC AUC 754 = AD 1 AUC 1000 = AD 247 AUC 1229 = AD 476 AUC 2206 = AD 1453 AUC 2753 = AD 2000 AUC 2772 = AD 2019 List of Latin phrases
Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics and chemistry in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, stars, nebulae and comets. More all phenomena that originate outside Earth's atmosphere are within the purview of astronomy. A related but distinct subject is physical cosmology, the study of the Universe as a whole. Astronomy is one of the oldest of the natural sciences; the early civilizations in recorded history, such as the Babylonians, Indians, Nubians, Chinese and many ancient indigenous peoples of the Americas, performed methodical observations of the night sky. Astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, the making of calendars, but professional astronomy is now considered to be synonymous with astrophysics. Professional astronomy is split into theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, analyzed using basic principles of physics.
Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain observational results and observations being used to confirm theoretical results. Astronomy is one of the few sciences in which amateurs still play an active role in the discovery and observation of transient events. Amateur astronomers have made and contributed to many important astronomical discoveries, such as finding new comets. Astronomy means "law of the stars". Astronomy should not be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects. Although the two fields share a common origin, they are now distinct. Both of the terms "astronomy" and "astrophysics" may be used to refer to the same subject. Based on strict dictionary definitions, "astronomy" refers to "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties," while "astrophysics" refers to the branch of astronomy dealing with "the behavior, physical properties, dynamic processes of celestial objects and phenomena."
In some cases, as in the introduction of the introductory textbook The Physical Universe by Frank Shu, "astronomy" may be used to describe the qualitative study of the subject, whereas "astrophysics" is used to describe the physics-oriented version of the subject. However, since most modern astronomical research deals with subjects related to physics, modern astronomy could be called astrophysics; some fields, such as astrometry, are purely astronomy rather than astrophysics. Various departments in which scientists carry out research on this subject may use "astronomy" and "astrophysics" depending on whether the department is affiliated with a physics department, many professional astronomers have physics rather than astronomy degrees; some titles of the leading scientific journals in this field include The Astronomical Journal, The Astrophysical Journal, Astronomy and Astrophysics. In early historic times, astronomy only consisted of the observation and predictions of the motions of objects visible to the naked eye.
In some locations, early cultures assembled massive artifacts that had some astronomical purpose. In addition to their ceremonial uses, these observatories could be employed to determine the seasons, an important factor in knowing when to plant crops and in understanding the length of the year. Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye; as civilizations developed, most notably in Mesopotamia, Persia, China and Central America, astronomical observatories were assembled and ideas on the nature of the Universe began to develop. Most early astronomy consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. From these observations, early ideas about the motions of the planets were formed, the nature of the Sun and the Earth in the Universe were explored philosophically; the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the geocentric model of the Ptolemaic system, named after Ptolemy.
A important early development was the beginning of mathematical and scientific astronomy, which began among the Babylonians, who laid the foundations for the astronomical traditions that developed in many other civilizations. The Babylonians discovered. Following the Babylonians, significant advances in astronomy were made in ancient Greece and the Hellenistic world. Greek astronomy is characterized from the start by seeking a rational, physical explanation for celestial phenomena. In the 3rd century BC, Aristarchus of Samos estimated the size and distance of the Moon and Sun, he proposed a model of the Solar System where the Earth and planets rotated around the Sun, now called the heliocentric model. In the 2nd century BC, Hipparchus discovered precession, calculated the size and distance of the Moon and inven
History is the study of the past as it is described in written documents. Events occurring before written record are considered prehistory, it is an umbrella term that relates to past events as well as the memory, collection, organization and interpretation of information about these events. Scholars who write about history are called historians. History can refer to the academic discipline which uses a narrative to examine and analyse a sequence of past events, objectively determine the patterns of cause and effect that determine them. Historians sometimes debate the nature of history and its usefulness by discussing the study of the discipline as an end in itself and as a way of providing "perspective" on the problems of the present. Stories common to a particular culture, but not supported by external sources, are classified as cultural heritage or legends, because they do not show the "disinterested investigation" required of the discipline of history. Herodotus, a 5th-century BC Greek historian is considered within the Western tradition to be the "father of history", along with his contemporary Thucydides, helped form the foundations for the modern study of human history.
Their works continue to be read today, the gap between the culture-focused Herodotus and the military-focused Thucydides remains a point of contention or approach in modern historical writing. In East Asia, a state chronicle, the Spring and Autumn Annals was known to be compiled from as early as 722 BC although only 2nd-century BC texts have survived. Ancient influences have helped spawn variant interpretations of the nature of history which have evolved over the centuries and continue to change today; the modern study of history is wide-ranging, includes the study of specific regions and the study of certain topical or thematical elements of historical investigation. History is taught as part of primary and secondary education, the academic study of history is a major discipline in university studies; the word history comes from the Ancient Greek ἱστορία, meaning'inquiry','knowledge from inquiry', or'judge'. It was in that sense; the ancestor word ἵστωρ is attested early on in Homeric Hymns, the Athenian ephebes' oath, in Boiotic inscriptions.
The Greek word was borrowed into Classical Latin as historia, meaning "investigation, research, description, written account of past events, writing of history, historical narrative, recorded knowledge of past events, narrative". History was borrowed from Latin into Old English as stær, but this word fell out of use in the late Old English period. Meanwhile, as Latin became Old French, historia developed into forms such as istorie and historie, with new developments in the meaning: "account of the events of a person's life, account of events as relevant to a group of people or people in general, dramatic or pictorial representation of historical events, body of knowledge relative to human evolution, narrative of real or imaginary events, story", it was from Anglo-Norman that history was borrowed into Middle English, this time the loan stuck. It appears in the 13th-century Ancrene Wisse, but seems to have become a common word in the late 14th century, with an early attestation appearing in John Gower's Confessio Amantis of the 1390s: "I finde in a bok compiled | To this matiere an old histoire, | The which comth nou to mi memoire".
In Middle English, the meaning of history was "story" in general. The restriction to the meaning "the branch of knowledge that deals with past events. With the Renaissance, older senses of the word were revived, it was in the Greek sense that Francis Bacon used the term in the late 16th century, when he wrote about "Natural History". For him, historia was "the knowledge of objects determined by space and time", that sort of knowledge provided by memory. In an expression of the linguistic synthetic vs. analytic/isolating dichotomy, English like Chinese now designates separate words for human history and storytelling in general. In modern German and most Germanic and Romance languages, which are solidly synthetic and inflected, the same word is still used to mean both'history' and'story'. Historian in the sense of a "researcher of history" is attested from 1531. In all European languages, the substantive history is still used to mean both "what happened with men", "the scholarly study of the happened", the latter sense sometimes distinguished with a capital letter, or the word historiography.
The adjective historical is attested from 1661, historic from 1669. Historians write in the context of their own time, with due regard to the current dominant ideas of how to interpret the past, sometimes write to provide lessons for their own society. In the words of Benedetto Croce, "All history is contemporary history". History is facilitated by the formation of a "true discourse of past" through the production of narrative and analysis of past events relating to the human race; the modern discipline of history is dedicated to the institutional production of this discourse. All events that are remembered and preserved in some authentic form constitute the historical record; the task of histori
Periodization is the process or study of categorizing the past into discrete, quantified named blocks of time. This is done in order to facilitate the study and analysis of history, understanding current and historical processes, causality that might have linked those events; this results in descriptive abstractions that provide convenient terms for periods of time with stable characteristics. However, determining the precise beginning and ending to any "period" is arbitrary, since it has changed over time over the course of history. To the extent that history is continuous and ungeneralizable, all systems of periodization are more or less arbitrary, yet without named periods, however clumsy or imprecise, past time would be nothing more than scattered events without a framework to help us understand them. Nations, cultures and individuals, each with their different remembered histories, are engaged in imposing overlapping unsystematized, schemes of temporal periodization; the division of history into "ages" or periods is old, recorded as early as the first development of writing.
The Sumerian King List operates with dynastic regnal eras. The classical division into a Golden Age, Silver Age, Bronze Age, Heroic Age and Iron Age goes back to Hesiod. One Biblical periodization scheme used in the Middle Ages was Saint Paul's theological division of history into three ages: the first before the age of Moses, but the most discussed periodization scheme of the Middle Ages was the Six Ages of the World, where every age was a thousand years counting from Adam to the present, with the present time being the sixth and final stage. Not only do periodizing blocks overlap, they seemingly conflict with or contradict one another; some have a cultural usage, others refer to prominent historical events, yet others are defined by decimal numbering systems. Other periods are named from talismanic individuals; some of these usages will be geographically specific. This is true of periodizing labels derived from individuals or ruling dynasties, such as the Jacksonian Era in America, the Meiji Era in Japan, or the Merovingian Period in France.
Cultural terms may have a limited reach. Thus the concept of the "Romantic period" is meaningless outside the Western world of Europe and European-influenced cultures. "the 1960s", though technically applicable to anywhere in the world according to Common Era numbering, has a certain set of specific cultural connotations in certain countries. For this reason it may be possible to say such things as "The 1960s never occurred in Spain"; this would mean that the sexual revolution, youth rebellion and so on never developed during that decade in Spain's conservative Roman Catholic culture and under Francisco Franco's authoritarian regime. It is often said, as the historian Arthur Marwick has, that "the 1960s" began in the late 1950s and ended in the early 1970s, his reason for saying this is that the cultural and economic conditions that define the meaning of the period covers more than the accidental fact of a 10-year block beginning with the number 6. This extended usage is termed the "long 1960s".
This usage derives from other historians who have adopted labels such as "the long 19th century" to reconcile arbitrary decimal chronology with meaningful cultural and social phases. An Eighteenth Century may run 1714–1789. Eric Hobsbawm has argued for what he calls "the short twentieth century", encompassing the period from the First World War through to the end of the Cold War. Similar problems attend other labels. Is it possible to use the term "Victorian" outside Britain, within, does her reign of 1837-1901 usefully constitute a historical period? It sometimes is used when it is thought that its connotations usefully describe the politics and economic conditions characteristic of the last two-thirds of the nineteenth century. Periodizing terms have negative or positive connotations that may affect their usage; this includes Victorian, which negatively suggests sexual repression and class conflict. Other labels such as Renaissance have positive characteristics; as a result, these terms sometimes extend in meaning.
Thus the English Renaissance is used for a period identical to the Elizabethan Period or reign of Elizabeth I, begins some 200 years than the Italian Renaissance. However the Carolingian Renaissance is said to have occurred during the reign of the Frankish king Charlemagne, his immediate successors. Other examples, neither of which constituted a "rebirth" in the sense of revival, are the American Renaissance of the 1820s-60s, referring to literature, the Harlem Renaissance of the 1920s, referring to literature but to music and the visual arts; the conception of a "rebirth" of Classical Latin learning is first credited to the Italian poet Petrarch, the father of Renaissance Humanism, but the conception of a rebirth has been in common use since Petrarch's time. The dominant usage of the word Renaissance refers to the cultural changes that occurred in Italy that culminated in the High Renaissance around 1500-1530; this concept applies dominantly to the visual arts, the work of Miche
The terms anno Domini and before Christ are used to label or number years in the Julian and Gregorian calendars. The term anno Domini is Medieval Latin and means "in the year of the Lord", but is presented using "our Lord" instead of "the Lord", taken from the full original phrase "anno Domini nostri Jesu Christi", which translates to "in the year of our Lord Jesus Christ"; this calendar era is based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth, with AD counting years from the start of this epoch, BC denoting years before the start of the era. There is no year zero in this scheme, so the year AD 1 follows the year 1 BC; this dating system was devised in 525 by Dionysius Exiguus of Scythia Minor, but was not used until after 800. The Gregorian calendar is the most used calendar in the world today. For decades, it has been the unofficial global standard, adopted in the pragmatic interests of international communication and commercial integration, recognized by international institutions such as the United Nations.
Traditionally, English followed Latin usage by placing the "AD" abbreviation before the year number. However, BC is placed after the year number, which preserves syntactic order; the abbreviation is widely used after the number of a century or millennium, as in "fourth century AD" or "second millennium AD". Because BC is the English abbreviation for Before Christ, it is sometimes incorrectly concluded that AD means After Death, i.e. after the death of Jesus. However, this would mean that the approximate 33 years associated with the life of Jesus would neither be included in the BC nor the AD time scales. Terminology, viewed by some as being more neutral and inclusive of non-Christian people is to call this the Current or Common Era, with the preceding years referred to as Before the Common or Current Era. Astronomical year numbering and ISO 8601 avoid words or abbreviations related to Christianity, but use the same numbers for AD years; the Anno Domini dating system was devised in 525 by Dionysius Exiguus to enumerate the years in his Easter table.
His system was to replace the Diocletian era, used in an old Easter table because he did not wish to continue the memory of a tyrant who persecuted Christians. The last year of the old table, Diocletian 247, was followed by the first year of his table, AD 532; when he devised his table, Julian calendar years were identified by naming the consuls who held office that year—he himself stated that the "present year" was "the consulship of Probus Junior", 525 years "since the incarnation of our Lord Jesus Christ". Thus Dionysius implied that Jesus' incarnation occurred 525 years earlier, without stating the specific year during which his birth or conception occurred. "However, nowhere in his exposition of his table does Dionysius relate his epoch to any other dating system, whether consulate, year of the world, or regnal year of Augustus. Among the sources of confusion are: In modern times, incarnation is synonymous with the conception, but some ancient writers, such as Bede, considered incarnation to be synonymous with the Nativity.
The civil or consular year began on 1 January but the Diocletian year began on 29 August. There were inaccuracies in the lists of consuls. There were confused summations of emperors' regnal years, it is not known. Two major theories are that Dionysius based his calculation on the Gospel of Luke, which states that Jesus was "about thirty years old" shortly after "the fifteenth year of the reign of Tiberius Caesar", hence subtracted thirty years from that date, or that Dionysius counted back 532 years from the first year of his new table, it has been speculated by Georges Declercq that Dionysius' desire to replace Diocletian years with a calendar based on the incarnation of Christ was intended to prevent people from believing the imminent end of the world. At the time, it was believed by some that the resurrection of the dead and end of the world would occur 500 years after the birth of Jesus; the old Anno Mundi calendar theoretically commenced with the creation of the world based on information in the Old Testament.
It was believed that, based on the Anno Mundi calendar, Jesus was born in the year 5500 with the year 6000 of the Anno Mundi calendar marking the end of the world. Anno Mundi 6000 was thus equated with the resurrection and the end of the world but this date had passed in the time of Dionysius; the Anglo-Saxon historian the Venerable Bede, familiar with the work of Dionysius Exiguus, used Anno Domini dating in his Ecclesiastical History of the English People, completed in 731. In this same history, he used another Latin term, ante vero incarnationis dominicae tempus anno sexagesimo, equivalent to the English "before Christ", to identify years before the first year of this era. Both Dionysius and Bede regarded Anno Domini as beginning at the incarnation of Jesus, but "the distinction between Incarnation and Nativity was not drawn until the late 9th century, when in some places the Incarnation epoch was identified with Christ's conception, i.e. the Annunciation on March 25". On the continent of Europe, Anno
Art history is the study of objects of art in their historical development and stylistic contexts. The study includes painting, architecture, ceramics and other decorative objects. Art history is the history of different groups of people and their culture represented throughout their artwork. Art historians compare different time periods in art history; such as a comparison to Medieval Art to Renaissance Art. This history of cultures is shown in their art work in different forms. Art can be shown by attire, religion, sports. Or more visual pieces of art such as paintings, sculptures; as a term, art history encompasses several methods of studying the visual arts. Aspects of the discipline overlap; as the art historian Ernst Gombrich once observed, "the field of art history much like Caesar's Gaul, divided in three parts inhabited by three different, though not hostile tribes: the connoisseurs, the critics, the academic art historians". As a discipline, art history is distinguished from art criticism, concerned with establishing a relative artistic value upon individual works with respect to others of comparable style, or sanctioning an entire style or movement.
One branch of this area of study is aesthetics, which includes investigating the enigma of the sublime and determining the essence of beauty. Technically, art history is not these things, because the art historian uses historical method to answer the questions: How did the artist come to create the work?, Who were the patrons?, Who were his or her teachers?, Who was the audience?, Who were his or her disciples?, What historical forces shaped the artist's oeuvre, how did he or she and the creation, in turn, affect the course of artistic and social events? It is, questionable whether many questions of this kind can be answered satisfactorily without considering basic questions about the nature of art; the current disciplinary gap between art history and the philosophy of art hinders this inquiry. Art history is not only a biographical endeavor. Art historians root their studies in the scrutiny of individual objects, they thus attempt to answer in specific ways, questions such as: What are key features of this style?, What meaning did this object convey?, How does it function visually?, Did the artist meet their goals well?, What symbols are involved?, Does it function discursively?
The historical backbone of the discipline is a celebratory chronology of beautiful creations commissioned by public or religious bodies or wealthy individuals in western Europe. Such a "canon" remains prominent, as indicated by the selection of objects present in art history textbooks. Nonetheless, since the 20th century there has been an effort to re-define the discipline to be more inclusive of non-Western art, art made by women, vernacular creativity. Art history as we know it in the 21st century began in the 19th century but has precedents that date to the ancient world. Like the analysis of historical trends in politics and the sciences, the discipline benefits from the clarity and portability of the written word, but art historians rely on formal analysis, semiotics and iconography. Advances in photographic reproduction and printing techniques after World War II increased the ability of reproductions of artworks; such technologies have helped to advance the discipline in profound ways, as they have enabled easy comparisons of objects.
The study of visual art thus described, can be a practice that involves understanding context and social significance. Art historians employ a number of methods in their research into the ontology and history of objects. Art historians examine work in the context of its time. At best, this is done in a manner which respects imperatives. In short, this approach examines the work of art in the context of the world within which it was created. Art historians often examine work through an analysis of form; this approach examines how the artist uses a two-dimensional picture plane or the three dimensions of sculptural or architectural space to create his or her art. The way these individual elements are employed results in representational or non-representational art. Is the artist imitating an object or image found in nature? If so, it is representational; the closer the art hews to perfect imitation, the more the art is realistic. Is the artist not imitating, but instead relying on symbolism, or in an important way striving to capture nature's essence, rather than copy it directly?
If so the art is non-representational—also called abstract. Realism and abstraction exist on a continuum. Impressionism is an example of a representational style, not directly imitative, but strove to create an "impression" of nature. If the work is not representational and is an expression of the artist's feelings and aspirations, or is a search for ideals of beauty and form, the work is non-representational or a work of expressionism. An iconographical analysis is one. Through a close reading of such elements, it is possible to trace their lineage, with it draw conclusions regarding the origins and tra
Paleontology or palaeontology is the scientific study of life that existed prior to, sometimes including, the start of the Holocene Epoch. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments. 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, developed in the 19th century. The term itself originates from Greek παλαιός, palaios, "old, ancient", ὄν, on, "being, creature" and λόγος, logos, "speech, study". Paleontology lies on the border between biology and geology, but 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 and engineering. Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life all the way back to when Earth became capable of supporting life, about 3.8 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 the principal types of evidence about ancient life, 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 paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy. Classifying ancient organisms is difficult, as many do not fit well into the Linnaean taxonomy classifying living organisms, paleontologists more use cladistics to draw up evolutionary "family trees"; the final quarter of the 20th century saw the development of molecular phylogenetics, which investigates how organisms are related by measuring the similarity of the DNA in their genomes.
Molecular phylogenetics has 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, what they can tell us about the Earth's organic and inorganic past". Paleontology is one of the historical sciences, along with archaeology, astronomy, cosmology and history itself: it aims to describe phenomena of the past and reconstruct their causes. Hence it has three main elements: description of past phenomena; when trying to explain the past and other historical scientists construct a set of hypotheses about the causes and look for a smoking gun, a piece of evidence that accords with one hypothesis over the others. Sometimes the smoking gun is discovered by a fortunate accident during other research. For example, the discovery by Luis and Walter Alvarez of iridium, a extra-terrestrial metal, in the Cretaceous–Tertiary boundary layer made asteroid impact the most favored explanation for the Cretaceous–Paleogene extinction event, although the contribution of volcanism continues to be debated.
The other main type of science is experimental science, 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 experiment may disprove it, but the accumulation of failures to disprove is compelling evidence in favor. However, when confronted with unexpected phenomena, such as the first evidence for invisible radiation, experimental scientists use the same approach as historical scientists: construct a set of hypotheses about the causes and 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 has some overlap with archaeology, which works with objects made by humans and with human remains, while paleontologists are interested in the characteristics and evolution of humans as a species.
When dealing with evidence about humans and paleontologists may work together – for example paleontologists might identify animal or plant fossils around an archaeological site, to discover what the people who lived there ate. In addition, paleontology borrows techniques from other sciences, including biology, ecology, chemistry and mathematics. For example, geochemical signatures from rocks may help to discover when life first arose on Earth, analyses of carbon isotope ratios may help to identify climate changes and to explain major transitions such as the Permian–Triassic extinction event. A recent discipline, molecular phylogenetics, compares the DNA and RNA of modern organisms to re-construct the "family trees" of their