Radioactivarbon

Carbon-14 is a radioactive isotope of carbon used by archaeologists to date objects and remains. Carbon-14 is naturally occurring in the atmosphere. Plants take it up in respiration, in which they convert sugars made during photosynthesis back into energy that they use to grow and maintain other processes, according to Colorado State University. Animals incorporate carbon-14 into their bodies by eating plants or other plant-eating animals. Carbon-14 has a half-life of 5,730 years, meaning that after that time, half of the carbon-14 in a sample decays away, according to the University of Arizona.

Because organisms stop taking in carbon-14 after death, scientists can use carbon-14's half-life as a sort of clock to measure how long it has been since the organism died. This method works on once-living organisms, including objects made of wood or other plant material.

Who knew?

Carbon gets its name from the Latin word carbo, which means "coal."

Diamonds and graphite are among the hardest and softest natural materials known, respectively. The only difference between the two is their crystal structure.

Carbon makes up 0.032 percent of the Earth's lithosphere (crust and outer mantle) by weight, according to the Encyclopedia of Earth. A rough estimate of the weight of the lithosphere by La Salle University geologist David Smith is 300,000,000,000,000,000,000,000 (or 3*10^23) pounds, making the approximate weight of carbon in the lithosphere 10,560,000,000,000,000,000,000 (or 1.056*10^22) pounds.

Carbon dioxide (a carbon atom plus two oxygen atoms) makes up about 0.04 percent of Earth's atmosphere, according to the National Oceanic & Atmospheric Administration (NOAA) — an increase over pre-industrial times, because of the burning of fossil fuels.

Carbon monoxide (a carbon atom plus one oxygen atom) is an odorless gas produced from the burning of fossil fuels. Carbon monoxide kills by binding to hemoglobin, the oxygen-carrying compound in the blood. Carbon monoxide bonds to hemoglobin 210 times more strongly than oxygen binds to hemoglobin, effectively crowding out oxygen and suffocating the tissues, according to a 2001 paper in the Journal of the Royal Society of Medicine.

Diamond, the flashiest version of carbon, is formed under great pressure deep in the Earth's crust. The largest gem-quality diamond ever found was the Cullinan diamond, which was discovered in 1905, according to the Royal Collection Trust. The uncut diamond was 3,106.75 carats. The largest gem cut from the stone, at 530.2 carats, is one of the Crown Jewels of the United Kingdom and is known as the Great Star of Africa.

The tattoos of Ötzi the Iceman, a 5,300-year-old corpse found frozen in the Alps, were inked from carbon, according to a 2009 study in the Journal of Archaeological Science. Small incisions in the skin were made, and charcoal rubbed in, perhaps as part of an acupuncture treatment.

Ongoing research

Carbon is a long-studied element, but that doesn't mean there isn't more to discover. In fact, the same element that our prehistoric ancestors burned as charcoal may be the key to next-generation tech materials.

In 1985, Rick Smalley and Robert Curl of Rice University in Texas and their colleagues discovered a new form of carbon. By vaporizing graphite with lasers, the scientists created a mysterious new molecule made of pure carbon, according to the American Chemical Society. This molecule turned out to be a soccer-ball-shaped sphere made of 60 carbon atoms. The research team named their discovery the buckminsterfullerene after an architect who designed geodesic domes. The molecule is now more commonly known as the "buckyball." The researchers who discovered it won a Nobel Prize in Chemistry in 1996. Buckyballs have been found to inhibit the spread of HIV, according to a study published in 2009 in the Journal of Chemical Information and Modeling; medical researchers are working to attach drugs, molecule-by-molecule, to buckyballs in order to deliver medicine directly to sites of infection or tumors in the body; this includes research by Columbia University, Rice University and others.  

Since then, other new, pure carbon molecules — called fullerenes — have been discovered, including elliptical-shaped "buckyeggs" and carbon nanotubes with amazing conductive properties. Carbon chemistry is still hot enough to capture Nobel Prizes: In 2010, researchers from Japan and the United States won one for figuring out how to link carbon atoms together using palladium atoms, a method that enables the manufacture of large, complex carbon molecules, according to the Nobel Foundation.

Scientists and engineers are working with these carbon nanomaterials to build materials straight out of science-fiction. A 2010 paper in the journal Nano Letters reports the invention of flexible, conductive textiles dipped in a carbon nanotube "ink" that could be used to store energy, perhaps paving the way for wearable batteries, solar cells and other electronics.

Perhaps one of the hottest areas in carbon research today, however, involves the "miracle material" graphene. Graphene is a sheet of carbon only one atom thick. It's the strongest material known while still being ultralight and flexible. And it conducts electricity better than copper.

Mass-producing graphene is a challenge, though researchers in April 2014 reported that they could make large amounts using nothing but a kitchen blender. If scientists can figure out how to make lots of graphene easily, the material could become huge in tech. Imagine flexible, unbreakable gadgets that also happen to be paper-thin. Carbon has come a long way from charcoal and diamonds, indeed.  

Carbon nanotubes

A carbon nanotube (CNT) is a minuscule, straw-like structure made of carbon atoms. These tubes are extremely useful in a wide variety of electronic, magnetic and mechanical technologies. The diameters of these tubes are so tiny that they are measured in nanometers. A nanometer is one-billionth of a meter — about 10,000 times smaller than a human hair.

Carbon nanotubes are at least 100 times stronger than steel, but only one-sixth as heavy, so they can add strength to almost any material, according to nanoScience Instruments. They are also better than copper at conducting electricity and heat.

Nanotechnology is being applied to the quest to turn seawater into drinking water. In a new study, scientists at Lawrence Livermore National Laboratory (LLNL) have developed a carbon nanotube process that can take the salt out of seawater far more efficiently than traditional technologies. 

For example, traditional desalination processes pump in seawater under high pressure, sending it through reverse osmosis membranes. These membranes then reject all large particles, including salts, allowing only clean water to pass through. However, these desalination plants are very expensive and can only process about 10 percent of a county's water needs, according to LLNL.

In the nanotube study, the scientists mimicked the way biological membranes are structured: essentially a matrix with pores inside the membrane. They used nanotubes that were particularly small — more than 50,000 times thinner than a human hair. These tiny nanotubes allow for a very high flux of water but are so narrow that only one water molecule can pass through the tube at a time. And most importantly, the salt ions are too big to fit through the tube.

The researchers think the new discovery has important implications for the next generation of both water purification processes and high-flux membrane technologies.

Carbon-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues to date archaeological, geological and hydrogeological samples. 

In this video excerpt from NOVA: "Hunting the Elements," New York Times technology columnist David Pogue explores how isotopes of carbon can be used to determine the age of once-living matter. Learn how variations in atomic structure form isotopes of an element and how the three natural isotopes of carbon differ from each other. Meet paleoclimatologist Scott Stine, who uses radiocarbon dating to study changes in climate. Find out what it means for an isotope to be radioactive and how the half-life of carbon-14 allows scientists to date organic materials.

This video is available in both English and Spanish audio, along with corresponding closed captions.

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Radiocarbon Dating

Related terms:

Genes

Chronology

Isotopes

Pottery

Proteins

Colonization

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Chronology, Stratigraphy, and Dating Methods in Archaeology

S. Shackley, in International Encyclopedia of the Social & Behavioral Sciences, 2001

4.1.3 Accelerator mass spectrometry (AMS) and radiocarbon

From the inception of radiocarbon dating, 14C ages of samples were calculated by decay counting in mainly scintillation counters. This requires a relatively large sample, depending on the amount of carbon remaining in that sample. By the late 1970s a number of researchers discovered that when accelerating sample atoms in the form of ions to much higher energies in particle accelerators, a much smaller sample was required to derive confident dates—in most cases only milligrams instead of tens of grams for scintillation counting. Both cyclotron and tandem accelerator mass spectrometers have been used to accomplish this, with tandem accelerators becoming the most popular. One additional advantage of acceleration is that the 'stripping process' disassociates all molecular species with the result that carbon isotopes can be isolated, and contamination minimized. AMS 14C dating theoretically may push the time frame back to 100,000, effectively overlapping 40Ar/39Ar laser fusion dating (Taylor and Aitken 1997).

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Sub-Saharan Africa, Archaeology of

J. Parkington, in International Encyclopedia of the Social & Behavioral Sciences, 2001

3 Regionality and the Appearance of Modern Humans

The transition from Earlier to Middle Stone Age assemblages is poorly understood, in part because it happened much before radiocarbon dating became useful and after the time period best suited to potassium argon dating. Many Middle Stone Age (MSA) sites are open sites difficult, in any case, to date. Most archaeologists presume that the assemblages without hand axes, characterized by some facetted platform flakes and radial and Levallois cores, first appear about 250,000 years ago, but there is much room for debate. The decision no longer to make hand axes or cleavers from about this time may signal the invention and dissemination of methods of mounting and hafting stone points onto wooden shafts. Assuming this required smaller stone components, we might interpret the many kinds of points, unretouched, unifacial, bifacial, leaf-shaped, hollow-based, tanged and serrated, as versions of the spear point. As Desmond Clark pointed out some time ago, regionalization of point 'style' characterizes the MSA and distinguishes it from the preceding Earlier Stone Age (ESA), where change was slow and dissemination of form more encompassing. For some archaeologists this regionality within the MSA, along with the more rapid replacement of one form by another, is a mark of symbolic storage, because it reflects decisions by presumably identity-conscious groups, choices that reflect not function but style, a first indication of 'them' and 'us.'

The most dramatic development in thinking about the African Middle Stone Age has been its remarkable rise, in Desmond Clark's words, 'from peripheral to paramount.' In the late 1960s, bolstered by a rather naive belief in the accuracy of some of the earliest radiocarbon results obtained, MSA assemblages were thought to be contemporary with Upper Palaeolithic assemblages in Europe. Because of the obvious similarities between MSA and Middle, rather than Upper, Palaeolithic stone tool technologies and types, this was taken as a reflection of Africa's backwardness in progressing along the (presumed standard) toolmaking trajectory. It was also wrongly believed at that time that the Kabwe (formerly Broken Hill) cranium and the Saldanha calvarium were 'African neanderthalers.' After Vogel and Beaumont began to doubt the radiocarbon 'dates' for MSA assemblages, new, more experimental dating techniques, such as luminescence and ESR dating, became available (see Chronology, Stratigraphy, and Dating Methods in Archaeology). These have shown that almost all of the MSA is beyond the range of radiocarbon dating and confirmed the rough contemporaneity of Middle Palaeolithic and Middle Stone Age. We should also not underestimate the impact of the genetic work on mitochondrial DNA of the mid 1980s on archaeologists' thinking about the age of the MSA and the significance of the morphology of associated hominid remains. The 'out of Africa' genetic model, a re-evaluation of the modernity of MSA hominids and new dating assessments for African MSA sites have transformed our understanding of the origins of anatomically and behaviorally modern people. In this process, Africa has emerged as paramount, the likely source area of modernity in both senses.

Central to this change of thinking has been the set of assemblages known to John Goodwin and referred to by him as Howiesons Poort. These formed part of the short-lived notion of a 'second intermediate' between the Middle and Later Stone Ages, but have been shown repeatedly to lie stratigraphically within the suite of MSA assemblages, most effectively at Klasies River (South Africa) main site. Howiesons Poort assemblages are MSA in that they contain radial cores and sub-triangular flakes with facetted platforms, but they have an interesting set of novel characters that make them, in some estimations, precocious manifestations of later stone tool making patterns. Unlike assemblages above and below them, for example, there is a tendency for tool makers to prefer finer grained rocks and to manufacture substantial numbers of blades, some of them punch-struck, from them. There are also many backed pieces, including segments, some of them microlithic, trapezes and truncated blades, and in some assemblages, burins. These assemblages are increasingly well dated to beyond 60,000 years, which has interesting implications for these 'Upper Palaeolithic-like' characteristics, which seem to appear in Europe, along with unquestionably modern people, some 20,000 or more years later.

The African Middle Stone Age, but not specifically the Howiesons Poort, is increasingly viewed as the product of anatomically modern people. From Dar es Soltan in the north to Klasies River main site in the south, MSA hominids are anatomically modern, as indeed, or nearly so, are their contemporaries at Middle Palaeolithic sites in southwest Asia. Klasies River main site is, in fact, the most persuasive example of a set of associations that constitute anatomical and behavioral modernity. A deep depositional pile that is unquestionably a shell midden, associations of foodwaste and stone tools with hearths, well dated by radiometric dates and faunal observations to Marine Isotope Stages 5 and 4, and with excellent stratigraphic associations of MSA artefacts, including a Howiesons Poort component, with enough hominid fragments to be sure of a modern morphology, sets the standard for claims about modernity. Elsewhere in southern Africa, MSA assemblages are associated with abundant, clearly utilized ochre, bone tools, and decorated pieces of ostrich eggshell. So far it is not clear whether the relative paucity of these kinds of associations elsewhere in Africa is due to incomplete survey, poor preservation or the geography of ancient innovations. Claims for MSA manufacture of bone harpoons at Katanda would, if confirmed, support the innovative character of African MSA people.

Why, we may wonder, has Africa become so clearly paramount, so definitively not peripheral in the evolutionary history of modern people. One possibility is the accumulating evidence for the necessary consumption of marine and freshwater foods as the nutritional substrate for intellectual advances. Rather than being a consequence of increased intelligence, something that modern people did, the regular gathering of shellfish and other marine and freshwater organisms, appears to be essential if people were to acquire the structural lipids necessary to build a bigger brain. Coastal, stream, and lakeside site locations have been the pattern in Africa since the time of early hominids: it may be as much the available foods as the accessibility of water that had significance. Because the earliest shell middens are located along the shores of the Mediterranean-type terrestrial ecosystems at the northern and southern extremities of Africa, it is from here that the surge to modernity may have been fueled.

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Microscopic Simulations in Various Fields

Moshe Levy, ... Sorin Solomon, in Microscopic Simulation of Financial Markets, 2000

6.7 MICROSCOPIC SIMULATION OF THE NEOLITHIC REVOLUTION

To exemplify the MS formalization of "softer" subjects, let us recount the story of the introduction of agriculture in Europe (New Scientist, 1997). Radiocarbon dating of artifacts associated with farming life shows that farming spread from Anatolia (now Turkey) to northern Europe in less than 2000 years (from 8 to 6 thousands years ago). This was termed as the "Neolithic Revolution" and it was associated, among other things, with the spread of the proto-indo-european language in Europe (Renfrew, 1990). It is still under fierce debate if this was accompanied by significant population migration and consequently by genetic stock influx. Among the theories proposed by the various groups (see, for instance, Cavalli-Sforza, Menozzi, and Piazza, 1996) in order to explain the spread of the Neolithic Revolution throughout Europe were the following:

•

Learning agriculture from neighbors (and transmitting it to other neighbors)

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Sons/daughters establishing farms next to parents farms

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Farmers moving inside unsowed territory, etc.

Most of the direct data relevant to these individual events is lost. However, the main feature that was established is that the archeological findings are incompatible with a simple diffusion mechanism. Indeed, simple diffusion would imply an expansion of the farming territory proportional to the square root of time, and a fuzzy boundary separating the farming territory from the unsowed territory. In reality, the speed of expansion was constant in time and it advanced along relatively sharp (though irregular) boundaries. Until now, the modeling of this problem involved mainly "continuum" approaches that did not lead to universally accepted conclusions. The crucial role of the individual agents (farmers, hunters) and events (learning farming, establishing farms, moving from one location to another) suggests the use of MS for deciding this debate in a definitive way.

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Recent Advances in Bone, Dentin, and Enamel Biochemistry

NOREEN TUROSS, in Identification of Pathological Conditions in Human Skeletal Remains (Second Edition), 2003

THE NONCOLLAGENOUS PROTEINS OF BONES AND TEETH

A large number of glycoproteins and proteoglycans reside in the matrices of bones, dentin, and enamel (Sasaki and Shimokawa 1995; Robey 1996). The noncollagenous extracellular proteins in bone include the often-overlooked products that derive from the extensive vasculature in bone and dentin. Immunoglobulins of the IgG class and albumin are absorbed by a variety of calcium phosphate phases, including hydroxyapatite, a property that positively effects preservation in the fossil record (Klein et al. 1980; Tuross 1993).

Osteocalcin, a protein that when secreted inhibits osteoblast function (Ducy et al. 2000), is a small (49 amino acid) product found in both bone and dentin (Price et al. 1976). This protein has an unusual posttranslational modification at glutamate in which an additional carboxyl group is added in a vitamin K dependent manner, producing an amino acid called gammacarboxyglutamic acid (gla) (Price et al. 1981). Based on experiments with mice in which the osteocalcin gene was removed (Ducy et al. 1996), osteocalcin is thought to participate in the regulation of mineralization or bone turnover, although its exact function remains unclear.

Another small gla-containing protein in bone is matrix gla protein (MGP). MGP has a much wider distribution in the body and may be ancestral to osteocalcin (Rice et al. 1994). MGP is tightly bound to other extracellular matrix products in bone and may contribute to some of the apparent preservation of gla in skeletal material (Ajie et al. 1991).

At the other end of the scale in terms of size, the leucinerich proteoglycans from bone, such as decorin and biglycan, are modified by the addition of glycosaminoglycans. These modifications produce a product that by gel electrophoresis appears both large (<100kDa) and heterogeneous (Fisher et al. 1987). Decorin is known to bind to collagen and is thought to effect collagen fibril formation (Pringle and Dodd 1990; Danielson et al. 1997).

Other phosphorylated noncollagenous proteins in bone, such as osteopontin and osteonectin (SPARC), may regulate cellular activity through direct cell binding. The sizes of these two proteins are within a few hundred daltons of each other on the basis of primary structure, but they differ in their electrophoretic separation because of differences in posttranslational modifications (Fisher et al. 1987). Osteopontin has been associated with the mechanism by which osteoclasts bind to bone, whereas the function of osteonectin in bone remains elusive (Sodek et al. 2000).

One of the interesting developments of the last decade is the discovery that two major noncollagenous proteins found in dentin are cleavage products from a single gene. Dentin phosphophoryn (DPP) and dentin sialoprotein (DSP) are produced by proteolytic cleavage of a single transcript produced from a single gene on chromosome 4 (MacDougall et al. 1997). Phosphoryn was the first noncollagenous protein identified in calcified tissue (DiMuzio and Veis 1978), and its complicated development and subsequent degradation in situ required over 20 years for a substantially complete characterization. In contrast, a unique phosphorylated dentin protein called dentin matrix protein I (DMPI) was found by screening a cDNA library of odontoblasts (George et al. 1993). Whereas DPP function is thought to involve the initiation of apatite crystals, roles for DSP and DMPI remain to be elucidated (Butler et al. 1997).

That proteins exist in enamel comes as a surprise to some paleopathologists. A set of proline-rich products called amelogenins has been known since the mid 1960s (Eastoe 1965). The nonamelogenin protein pool is the much smaller fraction in developing enamel and has been the source of lively literature discussions (e.g., Termine et al. 1980; Krebsbach et al. 1996).

In humans, the amelogenin gene is expressed by copies on the X and Y chromosome (Salido et al. 1992). Amelogenins from all known species exist as alternative splicing transcripts, a fact that, in retrospect, contributed significantly to the difficulty of characterizing this protein (Simmer and Snead 1995). This unusual enamel protein has become a standard for sex determination in forensic cases, and this application has met with some success when applied to archeological materials (Stone et al. 1996).

The amounts and distribution of the extracellular noncollagenous proteins in bone, dentin, and enamel vary widely with age, organism, and bone type (Fisher et al. 1987; Robinson et al. 1996; Gorski 1998). Unlike many of the noncollagenous proteins, osteocalcin tends to increase with age (Otawara and Price 1986). Woven bone, that tissue likely to be formed by various pathological processes, is enriched in two acidic phosphoproteins, whereas lamellar bone is enriched in osteocalcin (Gorski 1998). Two proteoglycans of bone, decorin and biglycan, also exhibit alterations in distribution through development (Bianco et al. 1990). Enamel protein changes dramatically both in content and character in the process of development (Robinson et al. 1998).

Paleopathologies Considerations

It may seem surprising that more work has not been done on the noncollagenous proteins in archeological skeletons, but the combination of low amounts of a specific protein (often in the microgram/gram range) and the relentless destructive power of many depositional environments contributes to the paucity of data in this field. The existence of a persistent noncollagen amino acid composition in fossil bones has been known for over 30 years (Wyckoff 1972), and there have been attempts to characterize this component in a variety of skeletons. Osteocalcin has been identified immunologically in a number of skeletons, but attempts to isolate the molecule for radiocarbon dating have not been successful (Ajie et al. 1991; Burky et al. 2000). Simulation experiments with humid heated bone produced well over a 50% loss of osteocalcin immunoreactivity in less than two years (Collins et al. 2000).

Immunoglobulins (IgG) have been purified from well preserved archeological bone and have been used in conjunction with DNA data to identify the infectious response in an individual infected by Treponema pallidum (Kolman et al. 1999). The combination of the specific infectious response in the skeleton and the PCR amplification under stringent controls of a DNA segment from the infectious agent is strong evidence of ancient disease. To obtain reliable immunological information from the 200-year-old skeletons, IgGs had to be purified over protein A columns. The need to purify noncollagenous proteins from bone to obtain accurate immunoassays derives from two factors: (1) the amount of extracted, degraded collagen is almost invariably much higher than modern bone and (2) both the high levels of collagen degradation products and the degradation products such as melanoidins can perturb immunological assays.

DNA retrieval in modern bone or dentin is not a common procedure. When modern tissues are used as controls in archeological or forensic analyses, most of the DNA recovered is likely from adhering soft tissue or blood (Tuross 1994). The compartmentalization of DNA in the calcified tissue of skeletons is a matter of some debate; it may alter with changes in mineralization, degree and type of cross-links formed, and environmental insults to the bone or tooth. In some cases, DNA has been recovered from bone without decalcifying agents (Fisher et al. 1993), but it is more common in archeological settings to require total decalcification of the bone or tooth to release any preserved DNA (Kolman and Tuross 2000).

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Sauer, Carl Ortwin (1889–1975)

M. Williams, in International Encyclopedia of the Social & Behavioral Sciences, 2001

2 Widening Horizons

All the time Sauer's horizons were getting wider, his ideas more speculative, and his ethical values more refined. Toward the end of the 1930s he wrote a slight, but ultimately influential, paper which was a sustained and biting critique of the destructive social and environmental impact that resulted from the predatory outreach of Europe, which had few counterparts at that time except, perhaps, in the writing of Karl Marx (Sauer 1938). He drew inspiration from the work of George Perkins Marsh on the human transformation of the earth and Ernst Friedrich's concept of Raubwirtschaft, or destructive exploitation (see Marsh [1865] 1965, Friedrich 1904). His experience and knowledge of Latin and Central America and their history suggested to him that the Spanish conquest had led to a devastating and permanent impoverishment of the land and of its cultures and societies. Disease, warfare and enslavement had disrupted traditional value systems. Thus, the diffusion of technologically superior societies could affect humans and their culture just as much as it could physical resources.

But two works more than any others established his world reputation and heralded a remarkable decade of multifaceted yet interrelated speculative understanding of the place of humans on earth. First was Agricultural Origins and Dispersals (Sauer 1952a) that flowered later into a string of publications into the human uses of the organic world, and early humans in the Americas from the Ice Age onward. Unfortunately, radiocarbon dating came too late to inform Sauer's writing, but although he may not have provided the answers, he defined the questions brilliantly.

Second, in 1956, with the collaboration of Marston Bates and Lewis Mumford, he masterminded the Princetown symposium on 'Man's Role in Changing the Face of the Earth,' the theme of which thereafter became his overriding interest. (See Mumford, Lewis (1895–1990).) All his learning and concerns culminated in this volume, and in his chapter 'The Agency of Man on Earth' (Sauer 1956). The capacity of humans to alter the natural environment—the 'deformation of the pristine'—the cult of progress and waste that stemmed from mass production ('commodity fetishism'), and the alien intrusion of humans into world ecology, were included. In contemporary terms, the theme was the degradation of the environment, and it was an early and influential statement. It also had another dimension: globally, the 'imperialism of production' was as bad as the old, colonial imperialism, and might ultimately be no better than Marxist totalitarianism; mass culture was eliminating not only biological diversity but also cultural diversity, and older and less robust societies. Somehow, humans had to rise above this mindless, short-term exploitative mode. 'The high moments of history have come not when man was concerned with the comforts and displays of the flesh but when his spirit was moved to grow in grace.' Therefore, what was needed was 'an ethic and aesthetic under which man, practising the qualities of prudence and moderation, may indeed pass on to posterity a good Earth' (Sauer 1956, p. 68).

His simply articulated ideas had a resonance with many activists and intellectuals, as well as Californian avant-garde poets and literati, who extolled his work as an example of cultural and ecological sensitivity and respect, tinged with deep historical insight and scholarship, and made attractive by his simple and pithy language. He also tapped a deep spring of feeling during the 1960s and 1970s at the time of Vietnam and student unrest with their concerns at the limits of the earth and technological/political power. Yet Sauer was a complex mix. He was congenitally nonconformist but deeply conservative, and although profoundly concerned with conservation was never formally an 'environmentalist,' and indeed, he thought the movement was little more than an 'ecological binge.'

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Emotion

Warren W. Tryon, in Cognitive Neuroscience and Psychotherapy, 2014

Normative Cases

I first discuss what can be considered as normative situations where emotion impacts cognition. In Chapter 4 Principle 7: Consonance and Dissonance we learned how emotion warps cognition. In this chapter we learned that emotions are unconsciously generated by subcortical structures. It therefore follows that unconscious emotions warp cognition. The fibers descending from the cortex to the amygdale are few, but the fibers ascending from the amygdale to the cortex are many. This anatomical fact further supports the ability of emotions to modify cognitions and to do so more effectively than cognitions can modify emotions. The normal process of emotions motivating us to cherry-pick among facts to support emotionally held positions discussed in Chapter 4 in connection with Principle 7: Consonance and Dissonance is potentiated to a form of empirical blindness when faith-based beliefs are involved. Religious beliefs produce some of the strongest emotions that people can experience, even unto martyrdom. The extent to which faith-based beliefs trump scientific consensus is clearly evident in the WNET documentary entitled 'The Revisionaries' that aired on 28 January 2013. A preview of this show can be seen at http://www.pbs.org/independentlens/revisionaries/. J. D. McLeroy, D. D. S, known as Don McLeroy in the video, is a self-proclaimed Young Creationist7 who believes that the world is just 6,000 years old and that humans once walked with dinosaurs, despite radiocarbon dating8 evidence showing that the earth is 4.54 ± 0.05 billion years old.9 When questioned about the age of the Earth, Don McLeroy replied 'I disagree with these experts. Someone has to stand up to them. Scientific consensus means nothing' (minute 23:50 out of 55:24 in the full video). Don is welcome to disagree with a body of experts, but he goes well beyond disagreement when he substitutes his personal faith-based emotion-infused beliefs for scientific consensus at Texas School Board10 Meetings where he helped dictate specific language to textbook publishers regarding what students will learn in school regarding evolution and social studies. By doing so he has imposed his religious beliefs on students beyond Texas as well.

To claim that scientific consensus means nothing is to categorically reject all possible evidence that such a consensus might be based on. Alternatively stated, no amount of evidence is now or ever will be sufficient to modify his faith-based conviction that the Bible is literally correct in every way, including the age of the Earth. This position is empirically blind in that it is independent of evidence. This makes so-called creation science not science at all because scientific hypotheses must be falsifiable. Creationists admit to no empirical fact that would falsify the Bible. Hence creationism is not a scientific hypothesis. Bible study is not biological science. This should end the debate over whether or not to teach creationism in biology classes but it has not yet done so, thereby revealing a consensus of other faith-based decisions.

Reasons to teach creationism took several forms in the video referred to above. One form of reasoning questioned the certainty with which evolutionary theory has been established by emphasizing that scientific theories are never completely proven because a new finding may emerge that falsifies the theory. Another form of reasoning questioned how life forms could have become so diverse. No mention of genetics and the mechanics of DNA were made. A third form of reasoning is emotion based. Don McLeroy claimed that he cannot understand why a particular woman who opposes the teaching of creationism is so fearful of Christian conservativism, implying that her opposition is purely emotional and consequently irrational. Don does not understand that he has projected11 his own fear onto her, for if the Bible is proved wrong about the age of the Earth, then perhaps it is wrong in other ways as well, and that allows one to question everything in the Bible. This would dissolve the bedrock and emotional security of the life he has built including his role as Sunday School teacher where he endeavors to convince the children in his care of the complete correctness and literal truth of every word in the Bible. More than that, the Saturday February 2, 2013 edition of The New York Times printed the following quote from Paul Broun 'all that stuff I was taught about evolution and embryology and the Big Bang theory, all that is lies, straight from the pit of hell' and that evolution is one of those 'lies to try to keep me and all the folks who were taught that from understanding that they need a savior' (p. 16). Such emotionally charged convictions are sufficient for some parents to home school their children to protect them from perceived evil thought to emanate from the pit of hell by distorting scientific evidence as necessary in order to support their Christian faith.

Another illustration of emotionally held beliefs leading to empirical blindness comes from the good people at the Flat Earth Society.12 The 'About the society link' reveals that 'The mission of the Flat Earth Society is to promote and initiate discussion of Flat Earth theory as well as archive Flat Earth literature'. Everyday experience for everyone on the planet is that the world is flat. The thought that people and trees at the equator are standing out at right angles and that people and trees in the southern hemisphere are standing on their heads is ridiculous. When I upend a glass of water the liquid spills out. So oceans in the northern hemisphere should slide to the equator and drop off while oceans in the southern hemisphere should simply fall away. These 'reasons' can be used to justify the view that the world is flat. Those pictures of Earth as the big blue marble could have been photo-shopped by the liberal media.

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Exploring vegetation in the fourth dimension

Fraser J.G. Mitchell, in Trends in Ecology & Evolution, 2011

An alternative to mapping

Accurate comparisons between sites, elucidating the timing of events and quantifying migration rates all require chronologies. These chronologies are built principally from radiocarbon dating, but it is not feasible to date every pollen sample; therefore, chronologies are developed from a subset of dated samples. Previously, most chronologies were developed by simple interpolation between specific points in time to generate dates for the intervening samples [31]. This approach fails to take account of the precision of the radiocarbon dates, which are reported as two standard deviations of the mean date derived from numerous analyses of the sample in the dating laboratory. In addition to this, variations in the production of 14C in the past mean that radiocarbon years are not exactly equivalent to calendar years (they vary in length) and so radiocarbon dates require calibration to calendar years, which can further impact on precision [32]. Bayesian modelling has been used to develop procedures to address these issues, notably OxCal and Bpeat [33,34]. Recently, Haslett and Parnell [35] developed a more sophisticated procedure that uses a stochastic linear interpolation process called Bchron to build chronologies that include estimates of precision.

Parnell et al. [36] illustrated the application of Bchron in exploring the timing of events in pollen sequences on an east–west transect of sites across Europe. For example, the early Holocene rise of alder (Alnus) at the sampled sites is depicted as a series of probability distributions, which show east to west ordering over time with the exception of the most westerly site, Llyn Cororion in Wales (Figure 2). Further analysis of the data set using Bchron enabled the strength of ordering to be assessed [36]. The attraction of this approach over pollen isochrone mapping is that the precision of the estimates of direction and rate of migration or population expansion are apparent and this example highlights how diachronous events, such as the early Holocene Alnus rise, can be investigated. Indeed, the exceptional behaviour of Alnus at Llyn Cororion warrants further investigation. The analysis of a wider array of sites and associated genetic analysis of European Alnus populations would provide a powerful test bed for hypotheses on the origins and spread of this tree in western Europe. This example considers only six sites (Figure 2), but with sufficient computational power this approach could be applied to larger data sets and could provide a more incisive approach to analysing the spatial dynamics of past vegetation than the mere mapping of interpolated pollen data.



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Figure 2. The development of probability distributions for the timing of the rise in Alnus using Bchron at six sites along a west– east transect through Europe. (a) Distribution map of sites (site names in (c)); (b) Alnus percentage pollen curves for two example sites (Llyn Cororion and Słopiec) with associated chronologies for the two sites constructed using Bchron with the timing of Alnus rise highlighted; (c) probability distributions for the age of the Alnus rise at all six sites in (a). Reproduced, with permission, from Parnell et al. [36].

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Special Issue: Long-term ecological research

K.J. Willis, ... H.J.B. Birks, in Trends in Ecology & Evolution, 2010

A sound chronological framework is essential in many aspects of palaeoenvironmental research. All dating methods depend on a measurable accumulation of physical changes, progressing at a known rate, from a condition known at the time of the event to be dated. Relevant time-dependent processes include the decay of radioisotopes, the in-growth of decay ('daughter') products, and a range of other physical changes. The lower age limit depends on the minimal detection limits of these changes and the upper limit on the time needed for the accumulation of changes to be complete. Commonly used methods include: radiocarbon dating (e.g. dating used for Figures 2–4), which gives the age at which incorporation of radiocarbon into material ceased (typically the death of a living organism, e.g. [83]); luminescence dating, which provides estimates of the time elapsed since sedimentary material was deposited [84] or pottery last fired [85]; and U-series methods, which date the point at which a sample becomes a chemically closed system, such that changes in the ratio of U to Th isotopes in the sample depend only on radioactive decay (used extensively for dating coral and speleothem records, e.g. [86,87]). In situations where discrete and identifiable incremental changes occur over known time periods (e.g. annual growth of tree rings, annual deposition of laminated lake sediments, seasonal snow accumulation bands in ice-cores), layer-counting methods have potential to provide highly precise (annual and sub-annual) and reliable age estimates, e.g. [88,89]. The accuracy and precision of the different radiometric methods vary considerably, and depend in part on the context in which the methods are applied. The use of multiple dating methods, each reliant on different physical mechanisms and different underlying assumptions, improves confidence in the overall chronology and is an approach now commonly applied.

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Environmental DNA Time Series in Ecology

Miklós Bálint, ... Diana Bowler, in Trends in Ecology & Evolution, 2018

Dynamics of Single Species

eDNA can provide a new data source on changes in spatial patterns of occurrence of species and may even potentially show changes in relative abundances through time. So far, this has been especially useful to understand processes related to colonizations and invasions. For example, the colonization route of the Americas by humans after the Last Glacial Maximum is a long-debated issue [31]. Shotgun sequencing (see Glossary) of eDNA from lake sediments (combined with radiocarbon dating, plant fossils, and pollen; Box 2) showed that the 1500-km corridor between the retreating Laurentide and Cordilleran ice sheets (along the present-day border between British Columbia and Alberta, Canada) became ecologically suitable for megaherbivores only after 12 600 years BP, considerably later than the first appearance of human settlements south of the ice sheets. This indicates that the first human colonizers used an alternative route along the Pacific coast. Similarly, Olajos et al. [38] showed with a continuous, 10 000-year-long eDNA time series from lake sediment cores that colonization by whitefish of a Swedish lake happened immediately after deglaciation from the Baltic sea, and not at a later time point.

The 'native' versus 'non-native' status of species is often a key consideration in conservation, but it is not easily defined over time frames longer than a few decades. Over periods of hundreds to thousands of years, the definition of (non)-native can actually be ambiguous, since human activities have had a variety of effects on species distributions [39]. There is clear potential for eDNA to contribute temporal data critical to establishing more subtle human influences on species distributions, and the impact of introduced species. Ficetola et al. used sediment eDNA to refine the invasion history of rabbits introduced to the Kerguelen island, and to show that their impact on the local vegetation exceeds the impact of recent climate change [40]. Beyond placing species on the native-to-non-native continuum, spatially and temporally explicit eDNA data can be used to address important questions about invasion ecology, such as the frequency of introduction and establishment events [41,42].

Abundance data contain more information on the dynamics of populations than presence/absence data and hence potentially allow for more powerful tests of the factors affecting populations. However, there are many challenges regarding the extraction of abundance information from eDNA. At the very least, eDNA could provide information on changes in species' relative abundances through time by using the number of sequenced eDNA reads as a quantitative index (see Box 3 for discussion of problems and solutions on abundance or biomass estimation). Long-term monitoring is occasionally able to capture the influence of extreme events on populations [43]. However, with the longer time series permitted by eDNA, the effect of extreme events on population abundances could be potentially better quantified. Population viability analysis (PVA) aims to estimate extinction risks of endangered species and assess the role of catastrophic events that cause sharp reductions in abundance [44]. However, catastrophic scenarios used in current PVA models are often arbitrary because the frequency distribution of catastrophes is usually unknown [44]. Single-species time series of relative abundances may also be used to study the value of early warning signals, such as slower recovery and increased variance, for predicting the switch to an alternative stable state [3].

Box 3

Challenges

Numerous challenges associated with eDNA have already received considerable attention: biases associated with PCR primers [32,34], detection issues [31] for contamination, nucleotide damage, and taxonomic assignment. These problems are relatively well reviewed (see, e.g., [20,22,32,33,37]). Here, we aim to discuss additional challenges that are less commonly mentioned in the literature.

Taphonomy

eDNA observations depend on preserving substrates. Particles that bind DNA may be transported and reworked by erosion [81]. The vertical movement of DNA (leaching) may confound the interpretation of eDNA data [37]. Some studies on soils find evidence of such movement [82,83], while others do not [84]. Leaching is less likely to be an issue in aquatic sediments [24].

Imperfect Sampling of eDNA

A species may be present at a site, but not detected (a false negative, [85]), or a species may be erroneously recorded due to contamination (a false positive). Imperfect eDNA sampling, particularly the issue of false positives, is challenging [86], but it is increasingly addressed with species occupancy models [38]. It is increasingly advocated to use positive standards (i.e., artificial samples with known taxonomic composition) and negative controls in all laboratory steps [87]. The sequence information from these may inform the parametrization of occupancy models.

Organismic Abundance/Biomass

The use of eDNA to examine changes in species abundance is in its infancy, but it holds great potential [58,88]. The most serious problems are (i) variation in the copy numbers of marker genes among and within species, (ii) temporal variation in DNA deposition and preservation, and (iii) differential detection probabilities of operational taxonomic units (OTUs) due to primer bias during the PCR (specific to metabarcoding: it makes cross-species comparisons potentially unreliable [89]). We expect that increase in genome data availability [67] will help to solve the first problem. A potential strategy from paleoecology that has been proposed to address the second problem is to standardize the read numbers of each OTU by the cumulative sum of OTU reads in a given sample. This standardization could help cancel out effects of temporal variation in sedimentation and decaying rates [90]. However, the robustness of this approach requires further investigation. A solution to the third, metabarcoding-specific problem might be to exploit the relationship between occurrence and abundance [91] with technical replicates (e.g., replicated PCRs): if a species occurs in more technical replicates of the same sample, it implies that this species also contributed more DNA to this sample [85]. This theoretically may not completely solve the problem since occurrence is also influenced by primer bias, although to a smaller extent than read abundances [89]. Many of the techniques that address similar issues for direct monitoring data (differential detection probabilities of species due to differences in behavior, morphology, or habitat) might also be applicable for eDNA [86]. Quantitative PCR [24] and digital droplet PCR [92] are further options to get better abundance/biomass data for single, or a few, species.

Dead or Alive?

Ecosystem functions can be inferred from microbial genes, but many microorganisms actually live in sediments. DNA is continuously released from recently dead cells and contributes to the eDNA pool [93]. For temporal inferences, it is important to separate long-dead versus recently dead DNA. There are three emerging solutions. (i) DNA may be extracted from both extracellular and intracellular fractions. Reads from the intracellular fraction are assumed to originate from alive organisms and removed [94]. A similar approach might be to co-extract DNA and RNA, and then remove RNA-reads from DNA reads since RNA must originate from living organisms [94]. (ii) DNA degrades with age and this may help authentication [95]. (iii) Studies may focus on microbes that require oxygen or light: their DNA must originate from dead organisms since they cannot live in sediments [25,96,97].

More than 3,500 years ago a catastrophic volcanic eruption struck ancient Thera, known today as the Greek island of Santorini. Ash and pumice rained across the Mediterranean, and tsunami waves rolled onto faraway shores in Crete. In the 1960s archaeologists on Santorini uncovered a Minoan settlement frozen in time, with vibrant wall frescoes decorating multistory houses, all buried by volcanic debris.

The eruption was one of the most powerful volcanic explosions of the past 10,000 years and a crucial time point of the Mediterranean Bronze Age. It is also a major area of controversy in archaeology; researchers have argued for decades over the date of this cataclysm.

Although it does not settle the debate, a recent adjustment to the radiocarbon-dating process narrows down the possibilities. This much anticipated new calibration curve, a set of data points used to convert radiocarbon-dating results into calendar years, is highlighted in a special August issue of Radiocarbon. Called IntCal20, it draws from nearly twice the data of the previous curve, from 2013—and may prompt scientists to reevaluate the age of sites, artifacts and events around the world.

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"It's a really massive increase in the data set, and with each revision our ability to confidently date the past improves," says Thomas Higham, a radiocarbon-dating specialist at the University of Oxford, who was not involved in the calibration effort. "A lot of people are excited about this new curve because it is going to give us the opportunity to sharpen our chronologies and understand more about the way the earth works and the way the earth has changed through time."

All living things absorb carbon 14, a radioactive carbon isotope that decays at a regular rate over time. This means that shells, bone, charcoal and other organic materials that archaeologists find contain a chemical timestamp. Discovered in the late 1940s, radiocarbon dating transformed the study of prehistory and became the gold standard for establishing chronologies in archaeology. A second revolution came when scientists realized atmospheric carbon 14 levels vary over time as the result of fluctuations in solar activity—and, more recently, atomic bombs and fossil-fuel burning. Thus, radiocarbon dates need to be calibrated against independent measurements, primarily from chunks of ancient wood. These have annual growth rings that scientists can directly tie to calendar years and can also analyze for radiocarbon.

Radiocarbon dating works by comparing the three different isotopes of carbon. Isotopes of a particular element have the same number of protons in their nucleus, but different numbers of neutrons. This means that although they are very similar chemically, they have different masses.