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Tuesday, September 29, 2015

Paleontology


From Wikipedia, the free encyclopedia

Paleontology or palaeontology (/ˌplɪɒnˈtɒləi/, /ˌplɪənˈtɒləi/ or /ˌpælɪɒnˈtɒləi/, /ˌpælɪənˈtɒləi/) is the scientific study of life existent prior to, and sometimes including, the start of the Holocene Epoch roughly 11,700 years before present. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments (their paleoecology). Paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. The term itself originates from Greek παλαιός, palaios, i.e. "old, ancient", ὄν, on (gen. ontos), i.e. "being, creature" and λόγος, logos, i.e. "speech, thought, study".[1]

Paleontology lies on the border between biology and geology, but differs from archaeology in that it excludes the study of morphologically modern humans. It now uses techniques drawn from a wide range of sciences, including biochemistry, mathematics and engineering. Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life, almost 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 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, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave body fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating, which provides absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy. Classifying ancient organisms is also difficult, as many do not fit well into the Linnean taxonomy that is commonly used for classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of molecular phylogenetics, which investigates how closely organisms are related by measuring how similar the DNA is in their genomes. Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend.

Overview


A palaeontologist at work at John Day Fossil Beds National Monument

The preparation of the fossilised bones of Europasaurus holgeri

The simplest definition is "the study of ancient life".[2] Paleontology seeks information about several aspects of past organisms: "their identity and origin, their environment and evolution, and what they can tell us about the Earth's organic and inorganic past".[3]

A historical science

Paleontology is one of the historical sciences, along with archaeology, geology, astronomy, cosmology, philology and history itself.[4] This means that it aims to describe phenomena of the past and reconstruct their causes.[5] Hence it has three main elements: description of the phenomena; developing a general theory about the causes of various types of change; and applying those theories to specific facts.[4]

When trying to explain past phenomena, paleontologists and other historical scientists often construct a set of hypotheses about the causes and then look for a smoking gun, a piece of evidence that indicates that one hypothesis is a better explanation than others. Sometimes the smoking gun is discovered by a fortunate accident during other research. For example, the discovery by Luis Alvarez and Walter Alvarez of an iridium-rich layer at the CretaceousTertiary boundary made asteroid impact and volcanism the most favored explanations for the Cretaceous–Paleogene extinction event.[5]

The other main type of science is experimental science, which is often said to work by conducting experiments to disprove hypotheses about the workings and causes of natural phenomena – note that this approach cannot confirm a hypothesis is correct, since some later experiment may disprove it. However, when confronted with totally unexpected phenomena, such as the first evidence for invisible radiation, experimental scientists often use the same approach as historical scientists: construct a set of hypotheses about the causes and then look for a "smoking gun".[5]

Related sciences

Paleontology lies on the boundary between biology and geology since paleontology focuses on the record of past life but its main source of evidence is fossils, which are found in rocks.[6] For historical reasons paleontology is part of the geology departments of many universities, because in the 19th century and early 20th century geology departments found paleontological evidence important for estimating the ages of rocks while biology departments showed little interest.[7]

Paleontology also has some overlap with archaeology, which primarily works with objects made by humans and with human remains, while paleontologists are interested in the characteristics and evolution of humans as organisms. When dealing with evidence about humans, archaeologists and paleontologists may work together – for example paleontologists might identify animal or plant fossils around an archaeological site, to discover what the people who lived there ate; or they might analyze the climate at the time when the site was inhabited by humans.[8]


Analyses using engineering techniques show that Tyrannosaurus had a devastating bite, but raise doubts about how fast it could move.

In addition paleontology often uses techniques derived from other sciences, including biology, osteology, ecology, chemistry, physics and mathematics.[2] For example, geochemical signatures from rocks may help to discover when life first arose on Earth,[9] and analyses of carbon isotope ratios may help to identify climate changes and even to explain major transitions such as the Permian–Triassic extinction event.[10] A relatively recent discipline, molecular phylogenetics, often helps by using comparisons of different modern organisms' DNA and RNA to re-construct evolutionary "family trees"; it has also been used to estimate the dates of important evolutionary developments, although this approach is controversial because of doubts about the reliability of the "molecular clock".[11] Techniques developed in engineering have been used to analyse how ancient organisms might have worked, for example how fast Tyrannosaurus could move and how powerful its bite was.[12][13] It is relatively commonplace to study fossils using X-ray microtomography[14] A combination of paleontology, biology, and archaeology, paleoneurology is the study of endocranial casts (or endocasts) of species related to humans to learn about the evolution of human brains.[15]

Paleontology even contributes to astrobiology, the investigation of possible life on other planets, by developing models of how life may have arisen and by providing techniques for detecting evidence of life.[16]

Subdivisions

As knowledge has increased, paleontology has developed specialised subdivisions.[17] Vertebrate paleontology concentrates on fossils of vertebrates, from the earliest fish to the immediate ancestors of modern mammals. Invertebrate paleontology deals with fossils of invertebrates such as molluscs, arthropods, annelid worms and echinoderms. Paleobotany focuses on the study of fossil plants, but traditionally includes the study of fossil algae and fungi. Palynology, the study of pollen and spores produced by land plants and protists, straddles the border between paleontology and botany, as it deals with both living and fossil organisms. Micropaleontology deals with all microscopic fossil organisms, regardless of the group to which they belong.[18]

Instead of focusing on individual organisms, paleoecology examines the interactions between different organisms, such as their places in food chains, and the two-way interaction between organisms and their environment.[19]  One example is the development of oxygenic photosynthesis by bacteria, which hugely increased the productivity and diversity of ecosystems.[20] This also caused the oxygenation of the atmosphere. Together, these were a prerequisite for the evolution of the most complex eukaryotic cells, from which all multicellular organisms are built.[21]

Paleoclimatology, although sometimes treated as part of paleoecology,[18] focuses more on the history of Earth's climate and the mechanisms that have changed it[22] – which have sometimes included evolutionary developments, for example the rapid expansion of land plants in the Devonian period removed more carbon dioxide from the atmosphere, reducing the greenhouse effect and thus helping to cause an ice age in the Carboniferous period.[23]

Biostratigraphy, the use of fossils to work out the chronological order in which rocks were formed, is useful to both paleontologists and geologists.[24] Biogeography studies the spatial distribution of organisms, and is also linked to geology, which explains how Earth's geography has changed over time.[25]

Sources of evidence

Body fossils

This Marrella specimen illustrates how clear and detailed the fossils from the Burgess Shale lagerstätte are.

Fossils of organisms' bodies are usually the most informative type of evidence. The most common types are wood, bones, and shells.[26] Fossilisation is a rare event, and most fossils are destroyed by erosion or metamorphism before they can be observed. Hence the fossil record is very incomplete, increasingly so further back in time. Despite this, it is often adequate to illustrate the broader patterns of life's history.[27] There are also biases in the fossil record: different environments are more favorable to the preservation of different types of organism or parts of organisms.[28] Further, only the parts of organisms that were already mineralised are usually preserved, such as the shells of molluscs. Since most animal species are soft-bodied, they decay before they can become fossilised. As a result, although there are 30-plus phyla of living animals, two-thirds have never been found as fossils.[29]

Occasionally, unusual environments may preserve soft tissues. These lagerstätten allow paleontologists to examine the internal anatomy of animals that in other sediments are represented only by shells, spines, claws, etc. – if they are preserved at all. However, even lagerstätten present an incomplete picture of life at the time. The majority of organisms living at the time are probably not represented because lagerstätten are restricted to a narrow range of environments, e.g. where soft-bodied organisms can be preserved very quickly by events such as mudslides; and the exceptional events that cause quick burial make it difficult to study the normal environments of the animals.[30] The sparseness of the fossil record means that organisms are expected to exist long before and after they are found in the fossil record – this is known as the Signor-Lipps effect.[31]

Trace fossils


Trace fossils consist mainly of tracks and burrows, but also include coprolites (fossil feces) and marks left by feeding.[26][32] Trace fossils are particularly significant because they represent a data source that is not limited to animals with easily fossilised hard parts, and they reflect organisms' behaviours. Also many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them.[33] Whilst exact assignment of trace fossils to their makers is generally impossible, traces may for example provide the earliest physical evidence of the appearance of moderately complex animals (comparable to earthworms).[32]

Geochemical observations

Geochemical observations may help to deduce the global level of biological activity, or the affinity of certain fossils. For example, geochemical features of rocks may reveal when life first arose on Earth,[9] and may provide evidence of the presence of eukaryotic cells, the type from which all multicellular organisms are built.[34] Analyses of carbon isotope ratios may help to explain major transitions such as the Permian–Triassic extinction event.[10]

Classifying ancient organisms

Levels in the Linnean taxonomy

Naming groups of organisms in a way that is clear and widely agreed is important, as some disputes in paleontology have been based just on misunderstandings over names.[36] Linnean taxonomy is commonly used for classifying living organisms, but runs into difficulties when dealing with newly discovered organisms that are significantly different from known ones. For example: it is hard to decide at what level to place a new higher-level grouping, e.g. genus or family or order; this is important since the Linnean rules for naming groups are tied to their levels, and hence if a group is moved to a different level it must be renamed.[37]

Paleontologists generally use approaches based on cladistics, a technique for working out the evolutionary "family tree" of a set of organisms.[36] It works by the logic that, if groups B and C have more similarities to each other than either has to group A, then B and C are more closely related to each other than either is to A. Characters that are compared may be anatomical, such as the presence of a notochord, or molecular, by comparing sequences of DNA or proteins. The result of a successful analysis is a hierarchy of clades – groups that share a common ancestor. Ideally the "family tree" has only two branches leading from each node ("junction"), but sometimes there is too little information to achieve this and paleontologists have to make do with junctions that have several branches. The cladistic technique is sometimes fallible, as some features, such as wings or camera eyes, evolved more than once, convergently – this must be taken into account in analyses.[35]

Evolutionary developmental biology, commonly abbreviated to "Evo Devo", also helps paleontologists to produce "family trees", and understand fossils.[38] For example, the embryological development of some modern brachiopods suggests that brachiopods may be descendants of the halkieriids, which became extinct in the Cambrian period.[39]

Estimating the dates of organisms

Paleontology seeks to map out how living things have changed through time. A substantial hurdle to this aim is the difficulty of working out how old fossils are. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating. This technique is our only means of giving rocks greater than about 50 million years old an absolute age, and can be accurate to within 0.5% or better.[40] Although radiometric dating requires very careful laboratory work, its basic principle is simple: the rates at which various radioactive elements decay are known, and so the ratio of the radioactive element to the element into which it decays shows how long ago the radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are a few volcanic ash layers.[40]

Consequently, paleontologists must usually rely on stratigraphy to date fossils. Stratigraphy is the science of deciphering the "layer-cake" that is the sedimentary record, and has been compared to a jigsaw puzzle.[41] Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil's age must lie between the two known ages.[42] Because rock sequences are not continuous, but may be broken up by faults or periods of erosion, it is very difficult to match up rock beds that are not directly next to one another. However, fossils of species that survived for a relatively short time can be used to link up isolated rocks: this technique is called biostratigraphy. For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period.[43] If rocks of unknown age are found to have traces of E. pseudoplanus, they must have a mid-Ordovician age. Such index fossils must be distinctive, be globally distributed and have a short time range to be useful. However, misleading results are produced if the index fossils turn out to have longer fossil ranges than first thought.[44] Stratigraphy and biostratigraphy can in general provide only relative dating (A was before B), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of the problems involved in matching up rocks of the same age across different continents.[45]

Family-tree relationships may also help to narrow down the date when lineages first appeared. For instance, if fossils of B or C date to X million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved more than X million years ago.

It is also possible to estimate how long ago two living clades diverged – i.e. approximately how long ago their last common ancestor must have lived  – by assuming that DNA mutations accumulate at a constant rate. These "molecular clocks", however, are fallible, and provide only a very approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved,[46] and estimates produced by different techniques may vary by a factor of two.[11]

Overview of the history of life

The evolutionary history of life stretches back to over 3,000 million years ago, possibly as far as 3,800 million years ago.[47] Earth formed about 4,570 million years ago and, after a collision that formed the Moon about 40 million years later, may have cooled quickly enough to have oceans and an atmosphere about 4,440 million years ago.[48] However, there is evidence on the Moon of a Late Heavy Bombardment from 4,000 to 3,800 million years ago. If, as seems likely, such a bombardment struck Earth at the same time, the first atmosphere and oceans may have been stripped away.[49] The oldest clear evidence of life on Earth dates to 3,000 million years ago, although there have been reports, often disputed, of fossil bacteria from 3,400 million years ago and of geochemical evidence for the presence of life 3,800 million years ago.[9][50] Some scientists have proposed that life on Earth was "seeded" from elsewhere,[51] but most research concentrates on various explanations of how life could have arisen independently on Earth.[52]
 

This wrinkled "elephant skin" texture is a trace fossil of a non-stromatolite microbial mat. The image shows the location, in the Burgsvik beds of Sweden, where the texture was first identified as evidence of a microbial mat.[53]

For about 2,000 million years microbial mats, multi-layered colonies of different types of bacteria, were the dominant life on Earth.[54] The evolution of oxygenic photosynthesis enabled them to play the major role in the oxygenation of the atmosphere[55] from about 2,400 million years ago. This change in the atmosphere increased their effectiveness as nurseries of evolution.[56] While eukaryotes, cells with complex internal structures, may have been present earlier, their evolution speeded up when they acquired the ability to transform oxygen from a poison to a powerful source of energy in their metabolism. This innovation may have come from primitive eukaryotes capturing oxygen-powered bacteria as endosymbionts and transforming them into organelles called mitochondria.[47][57] The earliest evidence of complex eukaryotes with organelles such as mitochondria, dates from 1,850 million years ago.[21]

Multicellular life is composed only of eukaryotic cells, and the earliest evidence for it is the Francevillian Group Fossils from 2,100 million years ago,[58] although specialisation of cells for different functions first appears between 1,430 million years ago (a possible fungus) and 1,200 million years ago (a probable red alga). Sexual reproduction may be a prerequisite for specialisation of cells, as an asexual multicellular organism might be at risk of being taken over by rogue cells that retain the ability to reproduce.[59][60]


Opabinia made the largest single contribution to modern interest in the Cambrian explosion.

The earliest known animals are cnidarians from about 580 million years ago, but these are so modern-looking that the earliest animals must have appeared before then.[61] Early fossils of animals are rare because they did not develop mineralised hard parts that fossilise easily until about 548 million years ago.[62] The earliest modern-looking bilaterian animals appear in the Early Cambrian, along with several "weird wonders" that bear little obvious resemblance to any modern animals. There is a long-running debate about whether this Cambrian explosion was truly a very rapid period of evolutionary experimentation; alternative views are that modern-looking animals began evolving earlier but fossils of their precursors have not yet been found, or that the "weird wonders" are evolutionary "aunts" and "cousins" of modern groups.[63] Vertebrates remained an obscure group until the first fish with jaws appeared in the Late Ordovician.[64][65]

The spread of life from water to land required organisms to solve several problems, including protection against drying out and supporting themselves against gravity.[66][67][68][69] The earliest evidence of land plants and land invertebrates date back to about 476 million years ago and 490 million years ago respectively.[68][70] The lineage that produced land vertebrates evolved later but very rapidly between 370 million years ago and 360 million years ago;[71] recent discoveries have overturned earlier ideas about the history and driving forces behind their evolution.[72] Land plants were so successful that they caused an ecological crisis in the Late Devonian, until the evolution and spread of fungi that could digest dead wood.[23]


At about 13 centimetres (5.1 in) the Early Cretaceous Yanoconodon was longer than the average mammal of the time.[73]

Birds are the last surviving dinosaurs.[74]

During the Permian period synapsids, including the ancestors of mammals, may have dominated land environments,[75] but the Permian–Triassic extinction event 251 million years ago came very close to wiping out complex life.[76] The extinctions were apparently fairly sudden, at least among vertebrates.[77] During the slow recovery from this catastrophe a previously obscure group, archosaurs, became the most abundant and diverse terrestrial vertebrates. One archosaur group, the dinosaurs, were the dominant land vertebrates for the rest of the Mesozoic,[78] and birds evolved from one group of dinosaurs.[74] During this time mammals' ancestors survived only as small, mainly nocturnal insectivores, but this apparent set-back may have accelerated the development of mammalian traits such as endothermy and hair.[79] After the Cretaceous–Paleogene extinction event 65 million years ago killed off the non-avian dinosaurs – birds are the only surviving dinosaurs – mammals increased rapidly in size and diversity, and some took to the air and the sea.[80][81][82]


A modern social insect collects pollen from a modern flowering plant.

Fossil evidence indicates that flowering plants appeared and rapidly diversified in the Early Cretaceous, between 130 million years ago and 90 million years ago.[83] Their rapid rise to dominance of terrestrial ecosystems is thought to have been propelled by coevolution with pollinating insects.[84] Social insects appeared around the same time and, although they account for only small parts of the insect "family tree", now form over 50% of the total mass of all insects.[85]

Humans evolved from a lineage of upright-walking apes whose earliest fossils date from over 6 million years ago.[86] Although early members of this lineage had chimp-sized brains, about 25% as big as modern humans', there are signs of a steady increase in brain size after about 3 million years ago.[87] There is a long-running debate about whether modern humans are descendants of a single small population in Africa, which then migrated all over the world less than 200,000 years ago and replaced previous hominine species, or arose worldwide at the same time as a result of interbreeding.[88]

Mass extinctions

Extinction intensity.svg Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Neogene
Marine extinction intensity during the Phanerozoic
%
Millions of years ago
Extinction intensity.svg Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Neogene
Apparent extinction intensity, i.e. the fraction of genera going extinct at any given time, as reconstructed from the fossil record (graph not meant to include recent epoch of Holocene extinction event)
Life on earth has suffered occasional mass extinctions at least since 542 million years ago. Although they are disasters at the time, mass extinctions have sometimes accelerated the evolution of life on earth. When dominance of particular ecological niches passes from one group of organisms to another, it is rarely because the new dominant group is "superior" to the old and usually because an extinction event eliminates the old dominant group and makes way for the new one.[89][90]

The fossil record appears to show that the rate of extinction is slowing down, with both the gaps between mass extinctions becoming longer and the average and background rates of extinction decreasing. However, it is not certain whether the actual rate of extinction has altered, since both of these observations could be explained in several ways:[91]
  • The oceans may have become more hospitable to life over the last 500 million years and less vulnerable to mass extinctions: dissolved oxygen became more widespread and penetrated to greater depths; the development of life on land reduced the run-off of nutrients and hence the risk of eutrophication and anoxic events; marine ecosystems became more diversified so that food chains were less likely to be disrupted.[92][93]
  • Reasonably complete fossils are very rare, most extinct organisms are represented only by partial fossils, and complete fossils are rarest in the oldest rocks. So paleontologists have mistakenly assigned parts of the same organism to different genera, which were often defined solely to accommodate these finds – the story of Anomalocaris is an example of this.[94] The risk of this mistake is higher for older fossils because these are often unlike parts of any living organism. Many "superfluous" genera are represented by fragments that are not found again, and these "superfluous" genera appear to become extinct very quickly.[91]
All genera
"Well-defined" genera
Trend line
"Big Five" mass extinctions
Other mass extinctions
Million years ago
Thousands of genera
Phanerozoic biodiversity as shown by the fossil record
Biodiversity in the fossil record, which is
"the number of distinct genera alive at any given time; that is, those whose first occurrence predates and whose last occurrence postdates that time"[95]
shows a different trend: a fairly swift rise from 542 to 400 million years ago, a slight decline from 400 to 200 million years ago, in which the devastating Permian–Triassic extinction event is an important factor, and a swift rise from 200 million years ago to the present.[95]

History of paleontology

This illustration of an Indian elephant jaw and a mammoth jaw (top) is from Cuvier's 1796 paper on living and fossil elephants.

Although paleontology became established around 1800, earlier thinkers had noticed aspects of the fossil record. The ancient Greek philosopher Xenophanes (570–480 BC) concluded from fossil sea shells that some areas of land were once under water.[96] During the Middle Ages the Persian naturalist Ibn Sina, known as Avicenna in Europe, discussed fossils and proposed a theory of petrifying fluids on which Albert of Saxony elaborated in the 14th century.[97] The Chinese naturalist Shen Kuo (1031–1095) proposed a theory of climate change based on the presence of petrified bamboo in regions that in his time were too dry for bamboo.[98]

In early modern Europe, the systematic study of fossils emerged as an integral part of the changes in natural philosophy that occurred during the Age of Reason. At the end of the 18th century Georges Cuvier's work established comparative anatomy as a scientific discipline and, by proving that some fossil animals resembled no living ones, demonstrated that animals could become extinct, leading to the emergence of paleontology.[99] The expanding knowledge of the fossil record also played an increasing role in the development of geology, particularly stratigraphy.[100]

The first half of the 19th century saw geological and paleontological activity become increasingly well organised with the growth of geologic societies and museums[101][102] and an increasing number of professional geologists and fossil specialists. Interest increased for reasons that were not purely scientific, as geology and paleontology helped industrialists to find and exploit natural resources such as coal.[103]

This contributed to a rapid increase in knowledge about the history of life on Earth and to progress in the definition of the geologic time scale, largely based on fossil evidence. In 1822 Henri Marie Ducrotay de Blanville, editor of Journal de Phisique, coined the word "palaeontology" to refer to the study of ancient living organisms through fossils.[104] As knowledge of life's history continued to improve, it became increasingly obvious that there had been some kind of successive order to the development of life. This encouraged early evolutionary theories on the transmutation of species.[105] After Charles Darwin published Origin of Species in 1859, much of the focus of paleontology shifted to understanding evolutionary paths, including human evolution, and evolutionary theory.[105]


Haikouichthys, from about 518 million years ago in China, may be the earliest known fish.[106]

The last half of the 19th century saw a tremendous expansion in paleontological activity, especially in North America.[107] The trend continued in the 20th century with additional regions of the Earth being opened to systematic fossil collection. Fossils found in China near the end of the 20th century have been particularly important as they have provided new information about the earliest evolution of animals, early fish, dinosaurs and the evolution of birds.[108] The last few decades of the 20th century saw a renewed interest in mass extinctions and their role in the evolution of life on Earth.[109] There was also a renewed interest in the Cambrian explosion that apparently saw the development of the body plans of most animal phyla. The discovery of fossils of the Ediacaran biota and developments in paleobiology extended knowledge about the history of life back far before the Cambrian.[63]

Increasing awareness of Gregor Mendel's pioneering work in genetics led first to the development of population genetics and then in the mid-20th century to the modern evolutionary synthesis, which explains evolution as the outcome of events such as mutations and horizontal gene transfer, which provide genetic variation, with genetic drift and natural selection driving changes in this variation over time.[110] Within the next few years the role and operation of DNA in genetic inheritance were discovered, leading to what is now known as the "Central Dogma" of molecular biology.[111] In the 1960s molecular phylogenetics, the investigation of evolutionary "family trees" by techniques derived from biochemistry, began to make an impact, particularly when it was proposed that the human lineage had diverged from apes much more recently than was generally thought at the time.[112] Although this early study compared proteins from apes and humans, most molecular phylogenetics research is now based on comparisons of RNA and DNA.[113]

Monday, September 28, 2015

Bioinorganic chemistry


From Wikipedia, the free encyclopedia

Bioinorganic chemistry is a field that examines the role of metals in biology. Bioinorganic chemistry includes the study of both natural phenomena such as the behavior of metalloproteins as well as artificially introduced metals, including those that are non-essential, in medicine and toxicology. Many biological processes such as respiration depend upon molecules that fall within the realm of inorganic chemistry. The discipline also includes the study of inorganic models or mimics that imitate the behaviour of metalloproteins.[1]
As a mix of biochemistry and inorganic chemistry, bioinorganic chemistry is important in elucidating the implications of electron-transfer proteins, substrate bindings and activation, atom and group transfer chemistry as well as metal properties in biological chemistry.

Composition of living organisms

About 99% of mammals' mass are the elements carbon, nitrogen, calcium, sodium, chlorine, potassium, hydrogen, phosphorus, oxygen and sulfur.[2] The organic compounds (proteins, lipids and carbohydrates) contain the majority of the carbon and nitrogen and most of the oxygen and hydrogen is present as water.[2] The entire collection of metal-containing biomolecules in a cell is called the metallome.

History

Paul Ehrlich used organoarsenic (“arsenicals”) for the treatment of syphilis, demonstrating the relevance of metals, or at least metalloids, to medicine, that blossomed with Rosenberg’s discovery of the anti-cancer activity of cisplatin (cis-PtCl2(NH3)2). The first protein ever crystallized (see James B. Sumner) was urease, later shown to contain nickel at its active site. Vitamin B12, the cure for pernicious anemia was shown crystallographically by Dorothy Crowfoot Hodgkin to consist of a cobalt in a corrin macrocycle. The Watson-Crick structure for DNA demonstrated the key structural role played by phosphate-containing polymers.

Themes in bioinorganic chemistry

Several distinct systems are of identifiable in bioinorganic chemistry. Major areas include:

Metal ion transport and storage

This topic covers a diverse collection of ion channels, ion pumps (e.g. NaKATPase), vacuoles, siderophores, and other proteins and small molecules which control the concentration of metal ions in the cells. One issue is that many metals that are metabolically required are not readily available owing to solubility or scarcity. Organisms have developed a number of strategies for collecting such elements and transporting them.

Enzymology

Many reactions in life sciences involve water and metal ions are often at the catalytic centers (active sites) for these enzymes, i.e. these are metalloproteins. Often the reacting water is a ligand (see metal aquo complex). Examples of hydrolase enzymes are carbonic anhydrase, metallophosphatases, and metalloproteinases. Bioinorganic chemists seek to understand and replicate the functi on of these metalloproteins.

Metal-containing electron transfer proteins are also common. They can be organized into three major classes: iron-sulfur proteins (such as rubredoxins, ferredoxins, and Rieske proteins), blue copper proteins, and cytochromes. These electron transport proteins are complementary to the non-metal electron transporters nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD). The nitrogen cycle make extensive use of metals for the redox interconversions.


4Fe-4S clusters serve as electron-relays in proteins.

Oxygen transport and activation proteins

Aerobic life make extensive use of metals such as iron, copper, and manganese. Heme is utilized by red blood cells in the form of hemoglobin for oxygen transport and is perhaps the most recognized metal system in biology. Other oxygen transport systems include myoglobin, hemocyanin, and hemerythrin. Oxidases and oxygenases are metal systems found throughout nature that take advantage of oxygen to carry out important reactions such as energy generation in cytochrome c oxidase or small molecule oxidation in cytochrome P450 oxidases or methane monooxygenase. Some metalloproteins are designed to protect a biological system from the potentially harmful effects of oxygen and other reactive oxygen-containing molecules such as hydrogen peroxide. These systems include peroxidases, catalases, and superoxide dismutases. A complementary metalloprotein to those that react with oxygen is the oxygen evolving complex present in plants. This system is part of the complex protein machinery that produces oxygen as plants perform photosynthesis.

Myoglobin is a prominent subject in bioinorganic chemistry, with particular attention to the iron-heme complex that is anchored to the protein.

Bioorganometallic chemistry

Bioorganometallic systems feature metal-carbon bonds as structural elements or as intermediates. Bioorganometallic enzymes and proteins include the hydrogenases, FeMoco in nitrogenase, and methylcobalamin. These naturally occurring organometallic compounds. This area is more focused on the utilization of metals by unicellular organisms. Bioorganometallic compounds are significant in environmental chemistry.[3]


Structure of FeMoco, the catalytic center of nitrogenase.

Metals in medicine

A number of drugs contain metals. This theme relies on the study of the design and mechanism of action of metal-containing pharmaceuticals, and compounds that interact with endogenous metal ions in enzyme active sites. The most widely used anti-cancer drug is cisplatin. MRI contrast agent commonly contain gadolinium. Lithium carbonate has been used to treat the manic phase of bipolar disorder. Gold antiarthritic drugs, e.g. auranofin have been commerciallized. Carbon monoxide-releasing molecules are metal complexes have been developed to suppress inflammation by releasing small amounts of carbon monoxide. The cardiovascular and neuronal importance of nitric oxide has been examined, including the enzyme nitric oxide synthase. (See also: nitrogen assimilation.)

Environmental chemistry

Environmental chemistry traditionally emphasizes the interaction of heavy metals with organisms. Methylmercury has caused major disaster called Minamata disease. Arsenic poisoning is a widespread problem owing largely to arsenic contamination of groundwater, which affects many millions of people in developing countries. The metabolism of mercury- and arsenic-containing compounds involves cobalamin-based enzymes.

Biomineralization

Biomineralization is the process by which living organisms produce minerals, often to harden or stiffen existing tissues. Such tissues are called mineralized tissues.[4][5][6] Examples include silicates in algae and diatoms, carbonates in invertebrates, and calcium phosphates and carbonates in vertebrates.Other examples include copper, iron and gold deposits involving bacteria. Biologically-formed minerals often have special uses such as magnetic sensors in magnetotactic bacteria (Fe3O4), gravity sensing devices (CaCO3, CaSO4, BaSO4) and iron storage and mobilization (Fe2O3•H2O in the protein ferritin). Because extracellular[7] iron is strongly involved in inducing calcification,[8][9] its control is essential in developing shells; the protein ferritin plays an important role in controlling the distribution of iron.[10]

Types of inorganic elements in biology

Alkali and alkaline earth metals


Like many antibiotics, monensin-A is an ionophore that tighlty bind Na+ (shown in yellow).[11]

The abundant inorganic elements act as ionic electrolytes. The most important ions are sodium, potassium, calcium, magnesium, chloride, phosphate, and the organic ion bicarbonate. The maintenance of precise gradients across cell membranes maintains osmotic pressure and pH.[12] Ions are also critical for nerves and muscles, as action potentials in these tissues are produced by the exchange of electrolytes between the extracellular fluid and the cytosol.[13] Electrolytes enter and leave cells through proteins in the cell membrane called ion channels. For example, muscle contraction depends upon the movement of calcium, sodium and potassium through ion channels in the cell membrane and T-tubules.[14]

Transition metals

The transition metals are usually present as trace elements in organisms, with zinc and iron being most abundant.[15][16][17] These metals are used in some proteins as cofactors and are essential for the activity of enzymes such as catalase and oxygen-carrier proteins such as hemoglobin.[18] These cofactors are bound tightly to a specific protein; although enzyme cofactors can be modified during catalysis, cofactors always return to their original state after catalysis has taken place. The metal micronutrients are taken up into organisms by specific transporters and bound to storage proteins such as ferritin or metallothionein when not being used.[19][20] Cobalt is essential for the functioning of vitamin B12.[21]

Main group compounds

Many other elements aside from metals are bio-active. Sulfur and phosphorus are required for all life. Phosphorus almost exclusively exists as phosphate and its various esters. Sulfur exists in a variety of oxidation states, ranging from sulfate (SO42−) down to sulfide (S2−). Selenium is a trace element involved in proteins that are antioxidants. Cadmium is important because of its toxicity.[22]

MIT Physicist Proposes New "Meaning of Life"

Original source:  http://bigthink.com/ideafeed/mit-physicist-proposes-new-meaning-of-life

MIT physicist Jeremy England claims that life may not be so mysterious after all, despite the fact it is apparently derived from non-living matter. In a new paper, England explains how simple physical laws make complex life more likely than not. In other words, it would be more surprising to find no life in the universe than a buzzing place like planet Earth.

What does all matter—rocks, plants, animals, and humans—have in common? We all absorb and dissipate energy. While a rock absorbs a small amount of energy before releasing what it doesn't use back into the universe, life takes in more energy and releases less. This makes life better at redistributing energy, and the process of converting and dissipating energy is simply a fundamental characteristic of the universe.
[S]imple physical laws make complex life more likely than not.
According to England, the second law of thermodynamics gives life its meaning. The law states that entropy, i.e. decay, will continuously increase. Imagine a hot cup of coffee sitting at room temperature. Eventually, the cup of coffee will reach room temperature and stay there: its energy will have dissipated. Now imagine molecules swimming in a warm primordial ocean. England claims that matter will slowly but inevitably reorganize itself into forms that better dissipate the warm oceanic energy.
[T]he second law of thermodynamics gives life its meaning.
The strength of England's theory is that it provides an underlying physical basis for Darwin's theory of evolution and helps explain some evolutionary tendencies that evolution cannot. Adaptations that don't clearly benefit a species in terms of survivability can be explained thusly: "the reason that an organism shows characteristic X rather than Y may not be because X is more fit than Y, but because physical constraints make it easier for X to evolve than for Y to evolve."

Sunday, September 27, 2015

Why Is There Something Rather Than Nothing

By Robert Adler
6 November 2014
Original source:  http://www.bbc.com/earth/story/20141106-why-does-anything-exist-at-all

People have wrestled with the mystery of why the universe exists for thousands of years. Pretty much every ancient culture came up with its own creation story - most of them leaving the matter in the hands of the gods - and philosophers have written reams on the subject. But science has had little to say about this ultimate question.

However, in recent years a few physicists and cosmologists have started to tackle it. They point out that we now have an understanding of the history of the universe, and of the physical laws that describe how it works. That information, they say, should give us a clue about how and why the cosmos exists.

Their admittedly controversial answer is that the entire universe, from the fireball of the Big Bang to the star-studded cosmos we now inhabit, popped into existence from nothing at all. It had to happen, they say, because "nothing" is inherently unstable.

This idea may sound bizarre, or just another fanciful creation story. But the physicists argue that it follows naturally from science's two most powerful and successful theories: quantum mechanics and general relativity.

Here, then, is how everything could have come from nothing.














(Credit: NASA, ESA, M. Postman (STScI), CLASH Team, Hubble Heritage Team (STScI/AURA))

Particles from empty space


First we have to take a look at the realm of quantum mechanics. This is the branch of physics that deals with very small things: atoms and even tinier particles. It is an immensely successful theory, and it underpins most modern electronic gadgets.

Quantum mechanics tells us that there is no such thing as empty space. Even the most perfect vacuum is actually filled by a roiling cloud of particles and antiparticles, which flare into existence and almost instantaneously fade back into nothingness.

These so-called virtual particles don't last long enough to be observed directly, but we know they exist by their effects.














The Stephan's Quintet group of galaxies (Credit: NASA, ESA, and the Hubble SM4 ERO Team)

Space-time, from no space and no time

From tiny things like atoms, to really big things like galaxies. Our best theory for describing such large-scale structures is general relativity, Albert Einstein's crowning achievement, which sets out how space, time and gravity work.

Relativity is very different from quantum mechanics, and so far nobody has been able to combine the two seamlessly. However, some theorists have been able to bring the two theories to bear on particular problems by using carefully chosen approximations. For instance, this approach was used by Stephen Hawking at the University of Cambridge to describe black holes.

    In quantum physics, if something is not forbidden, it necessarily happens

One thing they have found is that, when quantum theory is applied to space at the smallest possible scale, space itself becomes unstable. Rather than remaining perfectly smooth and continuous, space and time destabilize, churning and frothing into a foam of space-time bubbles.

In other words, little bubbles of space and time can form spontaneously. "If space and time are quantized, they can fluctuate," says Lawrence Krauss at Arizona State University in Tempe. "So you can create virtual space-times just as you can create virtual particles."

What's more, if it's possible for these bubbles to form, you can guarantee that they will. "In quantum physics, if something is not forbidden, it necessarily happens with some non-zero probability," says Alexander Vilenkin of Tufts University in Boston, Massachusetts.














Maybe it all began with bubbles (Credit: amira_a, CC by 2.0)

A universe from a bubble

So it's not just particles and antiparticles that can snap in and out of nothingness: bubbles of space-time can do the same. Still, it seems like a big leap from an infinitesimal space-time bubble to a massive universe that hosts 100 billion galaxies. Surely, even if a bubble formed, it would be doomed to disappear again in the blink of an eye?

    If all the galaxies are flying apart, they must once have been close together

Actually, it is possible for the bubble to survive. But for that we need another trick: cosmic inflation.


Most physicists now think that the universe began with the Big Bang. At first all the matter and energy in the universe was crammed together in one unimaginably small dot, and this exploded. This follows from the discovery, in the early 20th century, that the universe is expanding. If all the galaxies are flying apart, they must once have been close together.

Inflation theory proposes that in the immediate aftermath of the Big Bang, the universe expanded much faster than it did later. This seemingly outlandish notion was put forward in the 1980s by Alan Guth at the Massachusetts Institute of Technology, and refined by Andrei Linde, now at Stanford University.

    As weird as it seems, inflation fits the facts

The idea is that, a fraction of a second after the Big Bang, the quantum-sized bubble of space expanded stupendously fast. In an incredibly brief moment, it went from being smaller than the nucleus of an atom to the size of a grain of sand. When the expansion finally slowed, the force field that had powered it was transformed into the matter and energy that fill the universe today. Guth calls inflation "the ultimate free lunch".

As weird as it seems, inflation fits the facts rather well. In particular, it neatly explains why the cosmic microwave background, the faint remnant of radiation left over from the Big Bang, is almost perfectly uniform across the sky. If the universe had not expanded so rapidly, we would expect the radiation to be patchier than it is.














The cosmic microwave background
(Credit: NASA / WMAP Science Team)

The universe is flat and why that's important


Inflation also gave cosmologists the measuring tool they needed to determine the underlying geometry of the universe. It turns out this is also crucial for understanding how the cosmos came from nothing.

Einstein's theory of general relativity tells us that the space-time we live in could take three different forms. It could be as flat as a table top. It could curve back on itself like the surface of a sphere, in which case if you travel far enough in the same direction you would end up back where you started. Alternatively, space-time could curve outward like a saddle. So which is it?

There is a way to tell. You might remember from maths class that the three angles of a triangle add up to exactly 180 degrees. Actually your teachers left out a crucial point: this is only true on a flat surface. If you draw a triangle on the surface of a balloon, its three angles will add up to more than 180 degrees. Alternatively, if you draw a triangle on a surface that curves outward like a saddle, its angles will add up to less than 180 degrees.

So to find out if the universe is flat, we need to measure the angles of a really big triangle. That's where inflation comes in. It determined the average size of the warmer and cooler patches in the cosmic microwave background. Those patches were measured in 2003, and that gave astronomers a selection of triangles. As a result, we know that on the largest observable scale our universe is flat.














(Credit: It may not look flat... (Credit: NASA, ESA, and The Hubble Heritage Team (AURA/STScI))

It turns out that a flat universe is crucial. That's because only a flat universe is likely to have come from nothing.

Everything that exists, from stars and galaxies to the light we see them by, must have sprung from somewhere. We already know that particles spring into existence at the quantum level, so we might expect the universe to contain a few odds and ends. But it takes a huge amount of energy to make all those stars and planets.

    The energy of matter is exactly balanced by the energy of the gravity the mass creates

Where did the universe get all this energy? Bizarrely, it may not have had to get any. That's because every object in the universe creates gravity, pulling other objects toward it. This balances the energy needed to create the matter in the first place.

It's a bit like an old-fashioned measuring scale. You can put a heavy weight on one side, so long as it is balanced by an equal weight on the other. In the case of the universe, the matter goes on one side of the scale, and has to be balanced by gravity.

Physicists have calculated that in a flat universe the energy of matter is exactly balanced by the energy of the gravity the mass creates. But this is only true in a flat universe. If the universe had been curved, the two sums would not cancel out.














Matter on one side, gravity on the other (Credit: Da Sal, CC by 2.0)

Universe or multiverse?


At this point, making a universe looks almost easy. Quantum mechanics tells us that "nothing" is inherently unstable, so the initial leap from nothing to something may have been inevitable. Then the resulting tiny bubble of space-time could have burgeoned into a massive, busy universe, thanks to inflation. As Krauss puts it, "The laws of physics as we understand them make it eminently plausible that our universe arose from nothing - no space, no time, no particles, nothing that we now know of."

So why did it only happen once? If one space-time bubble popped into existence and inflated to form our universe, what kept other bubbles from doing the same?

    There could be a mind-boggling smorgasbord of universes

Linde offers a simple but mind-bending answer. He thinks universes have always been springing into existence, and that this process will continue forever.

When a new universe stops inflating, says Linde, it is still surrounded by space that is continuing to inflate. That inflating space can spawn more universes, with yet more inflating space around them. So once inflation starts it should make an endless cascade of universes, which Linde calls eternal inflation. Our universe may be just one grain of sand on an endless beach.

Those universes might be profoundly different to ours. The universe next door might have five dimensions of space rather than the three – length, breadth and height – that ours does. Gravity might be ten times stronger or a thousand times weaker, or not exist at all. Matter might be built out of utterly different particles.

So there could be a mind-boggling smorgasbord of universes. Linde says eternal inflation is not just the ultimate free lunch: it is the only one at which all possible dishes are available.

As yet we don't have hard evidence that other universes exist. But either way, these ideas give a whole new meaning to the phrase "Thanks for nothing".

Lawrence M. Krauss


From Wikipedia, the free encyclopedia

Lawrence M. Krauss
Laurence Krauss.JPG
Krauss at Ghent University, October 17, 2013
Born Lawrence Maxwell Krauss
(1954-05-27) May 27, 1954 (age 61)
New York, New York, USA
Nationality American
Fields
Institutions
Alma mater
Thesis Gravitation and phase transitions in the early universe (1982)
Doctoral advisor Roscoe Giles[1]
Known for
Notable awards Andrew Gemant Award (2001)
Lilienfeld Prize (2001)
Science Writing Award (2002)
Oersted Medal (2004)
Spouse
  • Katherine Kelley (1980–2012; divorced, 1 child)
  • Nancy Dahl (2014–present)
Website
krauss.faculty.asu.edu
Lawrence Maxwell Krauss (born May 27, 1954) is an American theoretical physicist and cosmologist who is Foundation Professor of the School of Earth and Space Exploration at Arizona State University and director of its Origins Project.[2] He is known as an advocate of the public understanding of science, of public policy based on sound empirical data, of scientific skepticism and of science education and works to reduce the impact of what he opines as superstition and religious dogma in pop culture.[3] Krauss is also the author of several bestselling books, including The Physics of Star Trek and A Universe from Nothing, and chairs the Bulletin of the Atomic Scientists Board of Sponsors.[4]

Biography

Early life and education

Krauss was born in New York City, but spent his childhood in Toronto, Ontario, Canada.[5] Krauss received undergraduate degrees in mathematics and physics with first class honours at Carleton University (Ottawa) in 1977, and was awarded a Ph.D. in physics at the Massachusetts Institute of Technology in 1982.[6][7]

Personal life

On January 19, 1980, he married Katherine Kelley, a native of Nova Scotia. Their daughter, Lilli was born November 23, 1984. Krauss and Kelley separated in 2010 and were divorced in 2012. Krauss married Australian/American Nancy Dahl on January 7, 2014, and spends some of the Arizona summer in Australia at the Mount Stromlo Observatory.[8][9]

Career

After some time in the Harvard Society of Fellows, Krauss became an assistant professor at Yale University in 1985 and associate professor in 1988. He was named the Ambrose Swasey Professor of Physics, professor of astronomy, and was chairman of the physics department at Case Western Reserve University from 1993 to 2005. In 2006, Krauss led the initiative for the no-confidence vote against Case Western Reserve University's president Edward M. Hundert and provost Anderson by the College of Arts and Sciences faculty. On March 2, 2006, both no-confidence votes were carried: 131–44 against Hundert and 97–68 against Anderson.

In August 2008, Krauss joined the faculty at Arizona State University as a Foundation Professor in the School of Earth and Space Exploration at the Department of Physics in the College of Liberal Arts and Sciences. He also became the Director of the Origins Project, a university initiative.[10] In 2009, he helped inaugurate this initiative at the Origins Symposium, in which eighty scientists participated and three thousand people attended.[11]

Krauss appears in the media both at home and abroad to facilitate public outreach in science. He has also written editorials for The New York Times. As a result of his appearance in 2004 before the state school board of Ohio, his opposition to intelligent design has gained national prominence.[12]

Krauss attended and was a speaker at the Beyond Belief symposia in November 2006 and October 2008. He served on the science policy committee for Barack Obama's first (2008) presidential campaign and, also in 2008, was named co-president of the board of sponsors of the Bulletin of the Atomic Scientists. In 2010, he was elected to the board of directors of the Federation of American Scientists, and in June 2011, he joined the professoriate of the New College of the Humanities, a private college in London.[13] In 2013, he accepted a part-time professorship at the Research School of Astronomy and Astrophysics in the Physics Department of the Australian National University.[9]

Krauss is a critic of string theory, which he discusses in his 2005 book Hiding in the Mirror.[14] Another book, released in March 2011, was titled Quantum Man: Richard Feynman's Life in Science, while A Universe from Nothing —with an afterword by Richard Dawkins—was released in January 2012 and became a New York Times bestseller within a week. Originally, its foreword was to have been written by Christopher Hitchens, but Hitchens grew too ill to complete it.[15][16] The paperback version of the book appeared in January 2013 with a new question-and-answer section and a preface integrating the 2012 discovery of the Higgs boson at the LHC.

A July 2012 article in Newsweek, written by Krauss, indicates how the Higgs particle is related to our understanding of the Big Bang. He also wrote a longer piece in the New York Times explaining the science behind and significance of the particle.[17]

Scientific work


Krauss lecturing about cosmology at TAM 2012

Krauss mostly works in theoretical physics and has published research on a great variety of topics within that field. His primary contribution is to cosmology as one of the first physicists to suggest that most of the mass and energy of the universe resides in empty space, an idea now widely known as "dark energy". Furthermore, Krauss has formulated a model in which the universe could have potentially come from "nothing," as outlined in his 2012 book A Universe from Nothing. He explains that certain arrangements of relativistic quantum fields might explain the existence of the universe as we know it while disclaiming that he "has no idea if the notion [of taking quantum mechanics for granted] can be usefully dispensed with".[18] As his model appears to agree with experimental observations of the universe (such as of its shape and energy density), it is referred to as a "plausible hypothesis".[19][20]

Initially, Krauss was skeptical of the Higgs mechanism. However, after the existence of the Higgs boson was confirmed by CERN, he has been researching the implications of the Higgs field on the nature of dark energy.[21]

Atheist activism

Krauss describes himself as an antitheist[22] and takes part in public debates on religion. Krauss featured in the 2013 documentary The Unbelievers, in which he and Richard Dawkins travel across the globe speaking publicly about the importance of science and reason as opposed to religion and superstition. The documentary also contains short clips of prominent figures such as Ayaan Hirsi Ali, Cameron Diaz, Sam Harris, and Stephen Hawking.[23]

In his book, A Universe from Nothing: Why There is Something Rather than Nothing (2012), Krauss discusses the premise that something cannot come from nothing, which has often been used as an argument for the existence of a Prime mover. He has since argued in a debate with John Ellis and Don Cupitt that the laws of physics allow for the universe to be created from nothing. "What would be the characteristics of a universe that was created from nothing, just with the laws of physics and without any supernatural shenanigans? The characteristics of the universe would be precisely those of the ones we live in." [24] In an interview with The Atlantic, however, he states that he has never claimed that "questions about origins are over." According to Krauss, "I don't ever claim to resolve that infinite regress of why-why-why-why-why; as far as I'm concerned it's turtles all the way down."[25]

Krauss has participated in many debates with theologians and apologists, including William Lane Craig and Hamza Tzortzis.[26] The debate with Tzortzis resulted in controversy when Krauss complained to the iERA organisers about the gender segregation of the audience; he only stayed when men and women were allowed to sit together.[27] Later, in discussions around secular liberal democracies and homosexuality, Krauss was asked "Why is incest wrong?" and answered that "Generally incest produces genetic defects" leading to "an ingrained incest taboo in almost all societies" though it could be theoretically permissible under rare circumstances where contraception is used.[28][29]

Honors

Krauss is one of the few living physicists described by Scientific American as a "public intellectual"[20] and he is the only physicist to have received awards from all three major American physics societies: the American Physical Society, the American Association of Physics Teachers, and the American Institute of Physics. In 2012, he was awarded the National Science Board's Public Service Medal for his contributions to public education in science and engineering in the United States.[30]

During December 2011, Krauss was named as a non-voting honorary board member for the Center for Inquiry.[31]

Bibliography

Krauss has authored or co-authored more than three hundred scientific studies and review articles on cosmology and theoretical physics.

Books

Contributor

  • 100 Things to Do Before You Die (plus a few to do afterwards). 2004. Profile Books.
  • The Religion and Science Debate: Why Does It Continue? 2009. Yale Press.

Articles

  • THE ENERGY OF EMPTY SPACE THAT ISN'T ZERO. 2006. Edge.org [33]
  • A dark future for cosmology. 2007. Physics World.
  • The End of Cosmology. 2008. Scientific American.
  • The return of a static universe and the end of cosmology. 2008. International journal of modern physics.
  • Late time behavior of false vacuum decay: Possible implications for cosmology and metastable inflating states. 2008. Physical Review Letters.
  • Krauss, Lawrence M. (June 2010). "Why I love neutrinos". Scientific American 302 (6): 19. doi:10.1038/scientificamerican0610-34. 

Media

Documentary films

Television

Films

Awards


Krauss (right) during TAM9 in 2011, with Neil DeGrasse Tyson and Pamela Gay.

Cryogenics

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Cryogenics...