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Selected articles covering paleontology and human science, culture, and economics

A Marella fossil.
A Marella fossil.
Paleontology or palaeontology (/ˌpliɒnˈtɒləi, ˌpæli-, -ən-/) is the scientific study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments (their paleoecology). As a "historical science" it attempts to explain causes rather than conduct experiments to observe effects. 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 itself originates from Greek: παλαιός (palaios) meaning "old, ancient," ὄν, ὀντ- (on, ont-), meaning "being, creature" and λόγος (logos), meaning "speech, thought, study". Paleontology lies on the border between biology and geology. 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 all the way back to when Earth became capable of supporting life, about 3,800 million years ago. As knowledge has increased, paleontology has developed specialized 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, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave fossils. (see more...)


Illustration of trilobite fossils by Joachim Barrande.
Illustration of trilobite fossils by Joachim Barrande.
The history of paleontology traces the history of the effort to study the fossil record left behind by ancient life forms. Although fossils had been studied by scholars since ancient times, the nature of fossils and their relationship to life in the past became better understood during the 17th and 18th centuries. At the end of the 18th century the work of Georges Cuvier ended a long running debate about the reality of extinction and led to the emergence of paleontology as a scientific discipline.

The first half of the 19th century saw paleontological activity become increasingly well organized. This contributed to a rapid increase in knowledge about the history of life on Earth, and progress towards definition of the geologic time scale. 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. After Charles Darwin published Origin of Species in 1859, much of the focus of paleontology shifted to understanding evolutionary paths.

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, as demonstrated by a series of important discoveries in China near the end of the 20th century. There was also a renewed interest in the Cambrian explosion that saw the development of the body plans of most animal phyla. (see more...)


Cope (left) and Marsh (right).
Cope (left) and Marsh (right).

The Bone Wars is the name given to a period of intense fossil speculation and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope and Othniel Charles Marsh. The two paleontologists used underhanded methods to out-compete the other in the field, resorting to bribery, theft, and destruction of bones. The scientists also attacked each other in scientific publications, attempting to ruin the other's credibility and cut off his funding.

Originally colleagues who were civil to each other, Cope and Marsh became bitter enemies after several personal slights between them. Their pursuit of bones led them west to rich bone beds in Colorado, Nebraska, and Wyoming. From 1877 to 1892, both paleontologists used their wealth and influence to finance their own expeditions and to procure services and fossils from dinosaur hunters. By the end of the Bone Wars, both men exhausted their funds in fueling their intense rivalry.

Cope and Marsh were financially and socially ruined by their efforts to disgrace each other, but their contributions to science and the field of paleontology were massive; the scientists left behind tons of unopened boxes of fossils on their deaths. The feud between the two men led to over 142 new species of dinosaurs being discovered and described. The products of the Bone Wars resulted in an increase in knowledge of ancient life, and sparked the public's interest in dinosaurs, leading to continued fossil excavation in North America in the decades to come. Several historical books and fictional adaptations have also been published about this period of intense paleontological activity. (see more...)


Cope (left) and Marsh (right).
Cope (left) and Marsh (right).

Bone Sharps, Cowboys, and Thunder Lizards is a graphic novel written by Jim Ottaviani and illustrated by the company Big Time Attic. The book tells a slightly fictionalized account of the Bone Wars, a period of intense excavation, speculation, and rivalry which led to a greater understanding of dinosaurs in the western United States. This novel is the first semi-fictional work written by Ottaviani; previously, he had taken no creative license with the characters he depicted, portraying them strictly according to historical sources.

Bone Sharps follows the two scientists Edward Drinker Cope and Othniel Marsh as they engage in an intense rivalry for prestige. Ottaviani has Cope and Marsh interact and meet many important figures of the Gilded Age, from P. T. Barnum to U.S. Grant, as the two scientists pursue their hotheaded and sometimes illegal acquisitions of fossils. Unlike in his previous books, "the scientists are the bad guys this time". Upon release, the novel received praise from critics for its exceptional historical content, although some reviewers wished more fiction had been woven into the story. (see more...)


Photograph of Charles Darwin.
Photograph of Charles Darwin.
Charles Darwin (12 February 1809 – 19 April 1882) was an English naturalist and geologist, best known for his contributions to evolutionary theory. He established that all species of life have descended over time from common ancestors, and in a joint publication with Alfred Russel Wallace introduced his scientific theory that this branching pattern of evolution resulted from a process that he called natural selection, in which the struggle for existence has a similar effect to the artificial selection involved in selective breeding.

His five-year voyage on HMS Beagle established him as an eminent geologist whose observations and theories supported Charles Lyell's uniformitarian ideas. Darwin later published his theory of evolution with compelling evidence in his 1859 book On the Origin of Species, overcoming scientific rejection of earlier concepts of transmutation of species. By the 1870s the scientific community and much of the general public had accepted evolution as a fact. However, many favoured competing explanations and it was not until the emergence of the modern evolutionary synthesis from the 1930s to the 1950s that a broad consensus developed in which natural selection was the basic mechanism of evolution. In modified form, Darwin's scientific discovery is the unifying theory of the life sciences, explaining the diversity of life.

In recognition of Darwin's pre-eminence as a scientist, he was honoured with a major ceremonial funeral and buried in Westminster Abbey, close to John Herschel and Isaac Newton. Darwin has been described as one of the most influential figures in human history. (see more...)


Photograph of Edward Drinker Cope
Photograph of Edward Drinker Cope
Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Cope distinguished himself as a child prodigy, publishing his first scientific paper at the age of nineteen. Cope later married and moved from Philadelphia to Haddonfield, New Jersey, although Cope would maintain a residence and museum in Philadelphia in his later years.

Cope had little formal scientific training, and he eschewed a teaching position for field work. He made regular trips to the American West prospecting in the 1870s and 1880s, often as a member of United States Geological Survey teams. A personal feud between Cope and paleontologist Othniel Charles Marsh led to a period of intense fossil-finding competition now known as the Bone Wars. Cope's financial fortunes soured after failed mining ventures in the 1880s. He experienced a resurgence in his career toward the end of his life before dying in 1897.

Cope's scientific pursuits nearly bankrupted him, but his contributions helped to define the field of American paleontology. He was a prodigious writer, with 1,400 papers published over his lifetime, although his rivals would debate the accuracy of his rapidly published works. He discovered, described, and named more than 1,000 vertebrate species including hundreds of fishes and dozens of dinosaurs. His proposals on the origin of mammalian molars and for the gradual enlargement of mammalian species over geologic time ("Cope's Law") are notable among his theoretical contributions. (see more...)


The Tree of Life as depicted by Ernst Haeckel in The Evolution of Man (1879) illustrates the 19th-century view that evolution was a progressive process leading towards man.
The Tree of Life as depicted by Ernst Haeckel in The Evolution of Man (1879) illustrates the 19th-century view that evolution was a progressive process leading towards man.
Evolutionary thought, the conception that species change over time, has roots in antiquity. With the beginnings of biological taxonomy in the late 17th century, a new anti-Aristotelian approach to modern science challenged traditional essentialism. Naturalists began to focus on the variability of species; the emergence of paleontology with the concept of extinction further undermined the static view of nature. In the early 19th century, Jean-Baptiste Lamarck proposed the first fully formed theory of evolution.

In 1858, Charles Darwin and Alfred Russel Wallace published a new evolutionary theory that was explained in detail in Darwin's On the Origin of Species (1859). Unlike Lamarck, Darwin proposedcommon descent and a branching tree of life. The theory was based on the idea of natural selection, and it synthesized a broad range of evidence from animal husbandry, biogeography, geology, morphology, and embryology.

The debate over Darwin's work led to the rapid acceptance of the general concept of evolution, but the specific mechanism he proposed, natural selection, was not widely accepted until it was revived by developments in biology that occurred during the 1920s through the 1940s. Before that time most biologists argued that other factors were responsible for evolution. The synthesis of natural selection with Mendelian genetics during the 1920s and 1930s founded the new discipline of population genetics. Throughout the 1930s and 1940s, population genetics became integrated with other biological fields, resulting in a widely applicable theory of evolution that encompassed much of biology—the modern evolutionary synthesis. (see more...)


The title page of the 1859 edition of On the Origin of Species.
The title page of the 1859 edition of On the Origin of Species.
On the Origin of Species, published in 1859, is a work of scientific literature by Charles Darwin which is considered to be the foundation of evolutionary biology. Darwin's book introduced the scientific theory that populations evolve over the course of generations through a process of natural selection. It presented a body of evidence that the diversity of life arose by common descent through a branching pattern of evolution. Darwin included evidence that he had gathered on the Beagle expedition in the 1830s and his subsequent research findings. Ideas about the transmutation of species were controversial as they conflicted with beliefs that species were unchanging parts of a designed hierarchy and that humans were unique and unlike animals. The book was written for non-specialist readers and attracted widespread interest upon its publication. As Darwin was an eminent scientist, his findings were taken seriously and the evidence he presented generated scientific, philosophical, and religious discussion. Within two decades there was widespread scientific agreement that evolution, with a branching pattern of common descent, had occurred, but scientists were slow to give natural selection the significance that Darwin thought appropriate. During the "eclipse of Darwinism" from the 1880s to the 1930s, various other mechanisms of evolution were given more credit. With the development of the modern evolutionary synthesis in the 1930s and 1940s, Darwin's concept of evolutionary adaptation through natural selection became central to modern evolutionary theory, and it has now become the unifying concept of the life sciences. (see more...)


Stephen Jay Gould (September 10, 1941 – May 20, 2002) was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation. Gould spent most of his career teaching at Harvard University and working at the American Museum of Natural History in New York. In the later years of his life, Gould also taught biology and evolution at New York University.

Gould's most significant contribution to evolutionary biology was the theory of punctuated equilibrium, which he developed with Niles Eldredge in 1972. The theory proposes that most evolution is marked by long periods of evolutionary stability, which is punctuated by rare instances of branching evolution. The theory was contrasted against phyletic gradualism, the popular idea that evolutionary change is marked by a pattern of smooth and continuous change in the fossil record.

Most of Gould's research was based on the land snail genera Poecilozonites and Cerion. He also contributed to evolutionary developmental biology, and has received wide praise for his book Ontogeny and Phylogeny. In evolutionary theory he opposed strict selectionism, sociobiology as applied to humans, and evolutionary psychology. Gould was known by the general public mainly from his 300 popular essays in the magazine Natural History, and his books written for a non-specialist audience.

In April 2000, the US Library of Congress named him a "Living Legend". (see more...)


The evolution of tetrapods from fishes.
The evolution of tetrapods from fishes.
A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Because of the incompleteness of the fossil record, there is usually no way to know exactly how close a transitional fossil is to the point of divergence. Therefore, we can't assume transitional fossils are direct ancestors of more recent groups, though they are frequently used as models for such ancestors. In 1859, when Charles Darwin's On the Origin of Species was first published, the fossil record was poorly known. Indeed, Archaeopteryx was discovered just two years later and represents a classic transitional form between dinosaurs and birds. Many more transitional fossils have been discovered since then, and there is now abundant evidence of how all classes of vertebrates are related, much of it in the form of transitional fossils. The phrase missing link has been used extensively in popular writings on human evolution to refer to a perceived gap in the hominid evolutionary record. It is most commonly used to refer to any new transitional fossil finds. Scientists, however, do not use the term, as it refers to a pre-evolutionary view of nature. (see more...)


"Archaeoraptor" is the generic name informally assigned in 1999 to a fossil from China in an article published in National Geographic magazine. The magazine claimed that the fossil was a "missing link" between birds and terrestrial theropod dinosaurs. Even prior to this publication there had been severe doubts about the fossil's authenticity. It led to a scandal when evidence demonstrated it to be a forgery through further scientific study. The forgery was constructed from rearranged pieces of real fossils from different species. Zhou et al. found that the head and upper body actually belong to a specimen of the primitive fossil bird Yanornis. A 2002 study found that the tail belongs to a small winged dromaeosaur, Microraptor, named in 2000. The legs and feet belong to an as yet unknown animal. The "Archaeoraptor" scandal has ongoing ramifications. The scandal brought attention to illegal fossil deals conducted in China. It also highlighted the need for close scientific scrutiny of purported "missing links" published in journals which are not peer-reviewed. The fossil scandal has been used by creationists in attempts to cast doubt on evolutionary theory. Although "Archaeoraptor" was a forgery, many true examples of feathered dinosaurs have been found and demonstrate the evolutionary connection between birds and other theropods. (see more...)


William Beebe on an expedition to Guiana in 1917.
William Beebe on an expedition to Guiana in 1917.
William Beebe was an American naturalist, ornithologist, marine biologist, entomologist, explorer, and author. He is remembered for the numerous expeditions he conducted for the New York Zoological Society, his deep dives in the Bathysphere, and his prolific scientific writing for both academic and popular audiences.

Born in Brooklyn, New York Beebe left college before obtaining a degree in order to work at the then newly opened New York Zoological Park, where he was given the duty of caring for the zoo's birds. Beebe participated in a series of research expeditions, including one intended to document the world's pheasants. He published an account of his pheasant expedition titled A Monograph of the Pheasants.

During the course of his expeditions Beebe gradually developed an interest in marine biology, ultimately leading to his 1930s dives in the Bathysphere off the coast of Bermuda. These dives represented the first time a biologist observed deep-sea animals in their native environment. Later, Beebe returned to the tropics and founded a tropical research station which remains in operation as part of the Asa Wright Nature Centre. Beebe's research there continued until his death in 1962.

He is also remembered for several theories he proposed about avian evolution which are now regarded as having been ahead of their time, particularly his 1915 hypothesis that the evolution of bird flight passed through a four-winged or "Tetrapteryx" stage, which has been supported by the 2003 discovery of Microraptor gui. (see more...)


Two Iguanodon sculptures at the crystal palace.
Two Iguanodon sculptures at the crystal palace.
The Crystal Palace Dinosaurs, also known as Dinosaur Court, are a series of sculptures of extinct animals (including dinosaurs) and mammals in Crystal Palace Park, now in the London borough of Bromley. Commissioned in 1852 to accompany the Crystal Palace after its move from the Great Exhibition in Hyde Park and unveiled in 1854, they were the first dinosaur sculptures in the world, pre-dating the publication of Charles Darwin's On the Origin of Species by six years. While to varying degrees inaccurate by modern standards, the models were designed and sculpted by Benjamin Waterhouse Hawkins under the scientific direction of Sir Richard Owen, representing the latest scientific knowledge at the time. The models were classed as Grade II listed buildings from 1973, extensively restored in 2002, and upgraded to Grade I listed in 2007. The models represent fifteen genera of extinct animals, not all dinosaurs. They are from a wide range of geological ages, and include true dinosaurs, ichthyosaurs, and plesiosaurs mainly from the Mesozoic era, and some mammals from the more recent Cenozoic era. (see more...)


Brontosaurus by Charles R. Knight.
Brontosaurus by Charles R. Knight.
Cultural depictions of dinosaurs have been numerous since the word dinosaur was coined in 1842. The dinosaurs featured in books, films, television programs, artwork, and other media have been used for both education and entertainment. The depictions range from the realistic, as in the television documentaries of the 1990s and first decade of the 21st century, or the fantastic, as in the monster movies of the 1950s and 1960s.

The growth in interest in dinosaurs since the Dinosaur Renaissance has been accompanied by depictions made by artists working with ideas at the leading edge of dinosaur science, presenting lively dinosaurs and feathered dinosaurs as these concepts were first being considered. Cultural depictions of dinosaurs have been an important means of translating scientific discoveries to the public.

Cultural depictions have also created or reinforced misconceptions about dinosaurs and other prehistoric animals, such as inaccurately and anachronistically portraying a sort of "prehistoric world" where many kinds of extinct animals (from the Permian animal Dimetrodon to mammoths and cavemen) lived together, and dinosaurs living lives of constant combat.

Other misconceptions reinforced by cultural depictions came from a scientific consensus that has now been overturned, such as the alternate usage of dinosaur to describe something that is maladapted or obsolete, or dinosaurs as slow and unintelligent. (see more...)


Holotype material of Creosaurus atrox, more recently known as Allosaurus atrox.
Holotype material of Creosaurus atrox, more recently known as Allosaurus atrox.
There have been a number of potential species assigned to the carnosaurian dinosaur genus Allosaurus since its description in 1877 by Othniel Charles Marsh, but only a handful are still regarded as valid. Allosaurus was originally described from material from the Upper Jurassic Morrison Formation of the western United States of America; the type species A. fragilis became one of the best-known species of dinosaur. The genus Allosaurus was part of the Marsh/Cope "Bone Wars" of the late 19th century, and its taxonomy became increasingly confused due to the competition, with several genera and species named by Cope and Marsh now regarded as synonyms of Allosaurus or A. fragilis. Since the description of Allosaurus, scientists have proposed additional species from such far-flung locales as Portugal, Siberia, Switzerland, and Tanzania, and unnamed remains from Australia and China have also been assigned to the genus at one time or another. (see more...)


Portrait of Mary Anning
Portrait of Mary Anning
Mary Anning (1799 – 1847) was a British fossil collector, dealer, and palaeontologist who became known around the world for important finds she made in Jurassic marine fossil beds in the cliffs along the English Channel at Lyme Regis in the county of Dorset in Southwest England. Her work contributed to fundamental changes in scientific thinking about prehistoric life and the history of the Earth.

Mary Anning searched for fossils in the area's Blue Lias cliffs. Her discoveries included the first ichthyosaur skeleton correctly identified; the first two plesiosaur skeletons found; the first pterosaur skeleton located outside Germany; and important fish fossils. Her observations played a key role in the discovery that coprolites, known as bezoar stones at the time, were fossilised faeces. She also discovered that belemnite fossils contained fossilised ink sacs like those of modern cephalopods.

Anning did not fully participate in the scientific community of 19th-century Britain, who were mostly Anglican gentlemen. She struggled financially for much of her life. Her family was poor, and her father, a cabinetmaker, died when she was eleven. She became well known in geological circles in Britain, Europe, and America. Nonetheless, as a woman, she was not eligible to join the Geological Society of London and she did not always receive full credit for her scientific contributions. After her death in 1847, her unusual life story attracted increasing interest. (see more...)


The eponymous petrified wood at Petrified Forest National Park
The eponymous petrified wood at Petrified Forest National Park
Petrified Forest National Park is a United States national park in Navajo and Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about 146 square miles (380 km2), encompassing semi-desert shrub steppe as well as highly eroded and colorful badlands. The site, the northern part of which extends into the Painted Desert, was declared a national monument in 1906 and a national park in 1962. The Petrified Forest is known for its fossils, especially fallen trees that lived in the Late Triassic, about 225 million years ago. The sediments containing the fossil logs are part of the widespread and colorful Chinle Formation, from which the Painted Desert gets its name. Beginning about 60 million years ago, the Colorado Plateau, of which the park is part, was pushed upward by tectonic forces and exposed to increased erosion. All of the park's rock layers above the Chinle, except geologically recent ones found in parts of the park, have been removed by wind and water. In addition to petrified logs, fossils found in the park have included Late Triassic ferns, cycads, ginkgoes, and many other plants as well as fauna including giant reptiles called phytosaurs, large amphibians, and early dinosaurs. Paleontologists have been unearthing and studying the park's fossils since the early 20th century. (see more...)


Jurassic Park author Michael Crichton.
Jurassic Park author Michael Crichton.

Jurassic Park is a 1993 American science fiction adventure film directed by Steven Spielberg. It is the first installment of the Jurassic Park franchise. It is based on the 1990 novel of the same name by Michael Crichton, with a screenplay written by Crichton and David Koepp. The film centers on the fictional Isla Nublar, an islet located off Central America's Pacific Coast, near Costa Rica Nicaragua border, where a billionaire philanthropist and a small team of genetic scientists have created a wildlife park of cloned dinosaurs.

Following an extensive $65 million marketing campaign, which included licensing deals with 100 companies, Jurassic Park grossed over $900 million worldwide in its original theatrical run. It surpassed Spielberg's 1982 film E.T. the Extra-Terrestrial to become the highest-grossing film until Titanic (1997). Jurassic Park was well received by critics, who praised its special effects and Spielberg's direction but criticized the script. The film won more than 20 awards (including 3 Academy Awards), mostly for its visual effects. Jurassic Park is considered by many to be one of the greatest films of the 1990s and in some cases of all time, as well as a landmark in the vector of visual effects regarding its computer-generated imagery and animatronics.

Jurassic Park was followed by two sequels, The Lost World: Jurassic Park and Jurassic Park III, both of which were box office successes but received mixed critical responses. A third sequel, Jurassic World, is set for release on June 12, 2015. (see more...)


Jurassic Park III director Joe Johnston.
Jurassic Park III director Joe Johnston.
Jurassic Park III is a 2001 American science fiction adventure monster film. It is the third installment in the Jurassic Park franchise and a sequel to the 1997 film The Lost World: Jurassic Park. It is the series' first film that was not directed by Steven Spielberg nor based on a book by Michael Crichton (though numerous scenes in the film were ultimately taken from Crichton's novels Jurassic Park and The Lost World). The film takes place on Isla Sorna, off Central America's Pacific coast, the island featured in the second film, where a divorced couple has tricked Dr. Alan Grant into going in order to help them find their son. After the success of Spielberg's Jurassic Park, Joe Johnston expressed interest in directing a sequel, a film adaptation of The Lost World. Spielberg instead gave Johnston permission to direct the third film in the series, if there were to be one. Production of Jurassic Park III began on August 30, 2000. Upon its release, the film received mixed reviews, with many praising the visual effects and action scenes but finding the plot clichéd and unoriginal. Despite being less well-received than the previous films, Jurassic Park III was a box office success, grossing $368 million worldwide. (see more...)


The Palanga Amber Museum.
The Palanga Amber Museum.
The Palanga Amber Museum, near the Baltic Sea in Palanga, Lithuania, is a branch of the Lithuanian Art Museum. It is housed in the restored 19th-century Tiškevičiai Palace and is surrounded by the Palanga Botanical Garden. The museum's collection of amber comprises about 28,000 pieces, of which about 15,000 contain inclusions of insects, spiders, or plants. About 4,500 pieces of amber are exhibited; many of these are items of artwork and jewelry. The first floor is dedicated to displays that illustrate the formation and composition of amber. Amber in the area arose from deltaic deposits of rivers flowing from Fennoscandia in the Eocene Period, about 40 to 45 million years ago. The processes via which resin is changed into amber by microorganisms, oxidation, and polymerization are illustrated. Samples of microdrops and microicicles (i.e. "amber within amber") are among the displayed items. The museum holds Europe's third largest amber specimen, the "Sun Stone", of size 210x190x150 mm and weighing 3,526 grams, which has been stolen twice. Amber from other areas of the world is also part of the collection.(see more...)


An accelerator mass spectrometer, the most common machine used to measure carbon-14.
An accelerator mass spectrometer, the most common machine used to measure carbon-14.
Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon (14
C
), a radioactive isotope of carbon. The method was developed by Willard Libby in the late 1940s and soon became a standard tool for archaeologists. Libby received the Nobel Prize for his work in 1960. The radiocarbon dating method is based on the fact that radiocarbon is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting radiocarbon combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire 14
C
by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and from that point onwards the amount of 14
C
it contains begins to reduce as the 14
C
undergoes radioactive decay. Measuring the amount of 14
C
in a sample from a dead plant or animal such as piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died. The older a sample is, the less 14
C
there is to be detected, and because the half-life of 14
C
(the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by radiocarbon dating are around 50,000 years ago, although special preparation methods occasionally permit dating of older samples. (see more...)