Planetary scientists who have studied the effect claim that this might kill all large animal and higher plant life. Viewed from Earth, the Moon is just far enough away to have very nearly the same apparent-sized disk as the Sun. The angular size or solid angle of these two bodies match because, although the Sun's diameter is about times as large as the Moon's, it is also times more distant. The most widely accepted theory of the Moon's origin, the giant impact theory, states that it formed from the collision of a Mars-size protoplanet called Theia with the early Earth. This hypothesis explains among other things the Moon's relative lack of iron and volatile elements, and the fact that its composition is nearly identical to that of the Earth's crust.
A range of theoretical habitable zones with stars of different mass our Solar System at center. Scale is logarithmic, and planet sizes are not to scale. A planet that can sustain life is termed habitable, even if life did not originate there. The Earth provides the currently understood requisite conditions of liquid water, an environment where complex organic molecules can assemble, and sufficient energy to sustain metabolism. This biosphere is generally believed to have begun evolving about 3. Earth is the only place in the universe where life is known to exist.
Some scientists believe that Earth-like biospheres might be rare. On land, biomes are separated primarily by differences in latitude, height above sea level and humidity. Terrestrial biomes lying within the Arctic or Antarctic Circles, at high altitudes or in extremely arid areas are relatively barren of plant and animal life; species diversity reaches a peak in humid lowlands at equatorial latitudes. Some of these are non-renewable resources, such as mineral fuels, that are difficult to replenish on a short time scale.
Large deposits of fossil fuels are obtained from the Earth's crust, consisting of coal, petroleum, natural gas and methane clathrate. These deposits are used by humans both for energy production and as feedstock for chemical production. The Earth's biosphere produces many useful biological products for humans, including but far from limited to food, wood, pharmaceuticals, oxygen, and the recycling of many organic wastes.
The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends upon dissolved nutrients washed down from the land. In , human use of land is approximately: Arable Permanent Permanent Forests Urban Land use O land crops pastures and woodland areas. Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, blizzards, floods, droughts, and other calamities and disasters. Many localized areas are subject to human-made pollution of the air and water, acid rain and toxic substances, loss of vegetation overgrazing, deforestation, desertification , loss of wildlife, species extinction, soil degradation, soil depletion, erosion, and introduction of invasive species.
According to the United Nations, a scientific consensus exists linking human activities to global warming due to industrial carbon dioxide emissions. This is predicted to produce changes such as the melting of glaciers and ice sheets, more extreme temperature ranges, significant changes in weather and a global rise in average sea levels.
Surveying, the determination of locations and distances, and to a lesser extent navigation, the determination of position and direction, have developed alongside cartography and geography, providing and suitably quantifying the requisite information. Earth has approximately 6,,, human inhabitants as of December 12, Human population density varies widely around the world, but a majority live in Asia. This image is not photographic and many features are brighter than they would appear to a direct observer. Independent sovereign nations claim the planet's entire land surface, except for some parts of Antarctica and the odd unclaimed area of Bir Tawil between Egypt and Sudan.
As of there are sovereign states, including the United Nations member states. In addition, there are 59 dependent territories, and a number of autonomous areas, territories under dispute and other entities. The U. When the consensus of the membership permits, it provides a mechanism for armed intervention. The station's crew, currently six people, is usually replaced every six months.
Notas sobre o tempo, o clima e a diferença
The first photograph ever taken by astronauts of an "Earthrise", from Apollo 8 Main article: Earth in culture The name "Earth" derives from the Anglo-Saxon word erda, which means ground or soil, and is related to the German word erde. It became eorthe later, and then erthe in Middle English. In many cultures the mother goddess is also portrayed as a fertility deity.
Creation myths in many religions recall a story involving the creation of the Earth by a supernatural deity or deities. A variety of religious groups, often associated with fundamentalist branches of Protestantism or Islam, assert that their interpretations of these creation myths in sacred texts are literal truth and should be considered alongside or replace conventional scientific accounts of the formation of the Earth and the origin and development of life. In the past there were varying levels of belief in a flat Earth, but this was displaced by the concept of a spherical Earth due to observation and circumnavigation.
32nd Bienal de São Paulo () - Catalogue by Bienal São Paulo - Issuu
Books are collections of articles that can be downloaded or ordered in print. The quantities given are the values at the instant J That is, Based on data from the Vector Map and Global Landcover datasets, extreme values for coverage of lakes and streams are 0. The ice shields of Antarctica and Greenland are counted as land, even though much of the rock which supports them lies below sea level.
Blue, Jennifer Gazetteer of Planetary Nomenclature. However, it is confirmed to have existed on the surface of Mars in the past, and may still appear today. Daily Headlines University of Arkansas. See: Tinetti, G. Nature : — See: Chorowicz, Jean October Journal of African Earth Sciences 43 1—3 : — See the Challenger Deep article for more details. To first approximation, the average depth would be the ratio of the two, or 2. Astronomy and Astrophysics 2 : — So the. Myles; Williams, James C. International Astronomical Union Commission 4: Ephemerides. See table 8. Allen's Astrophysical Quantities.
David R. Handbook of Chemistry and Physics 81st ed. Global earth physics a handbook of physical constants. Surface area of our planet covered by oceans and continents. Table 8o University of British Columbia, Okanagan. The World Factbook. Central Intelligence Agency. Washington: American Geophysical Union. Cox, ed Allen's Astrophysical Quantities 4th ed.
Arizona State University. BBC Online. Science : — The Age of the Earth. California: Stanford University Press. Brent Geological Society, London, Special Publications — TalkOrigins Archive. Royal Society of Chemistry. BBC News. Science : Fall Meeting Abstract U51A American Geophysical Union. San Francisco: Astronomical Society of the Pacific. Continents and Supercontinents. Oxford University Press US. Jun ISSN Reviews of Geophysics 6: — Tectonophysics December Journal of Asian Earth Sciences Australian Journal of Earth Sciences — American Scientist — Ford; Worm, Boris February Scientific American 6 : 90— Journal of Atmospheric Sciences 22 3 : — Schopf, J.
Late Proterozoic low- latitude global glaciation: the Snowball Earth. October Bulletin of the Geological Society of America 1—2 : — Page Paleontology Science Center. Present and Future" PDF.
Secret Language of Belly Dancing
Astrophysical Journal — Bibcode: ApJ Icarus — PMC March Monthly Notices of the Royal Astronomical Society See also Palmer, Jason World Pool- Billiards Association. Professional Surveyor 20 5 : 16— The Lancet : — Australian Broadcasting Corporation. The Inaccessible Earth 2nd ed. Note: After Ronov and Yaroshevsky Proceedings of the National Academy of Science 71 12 : — Thomas J.
Crustal Structure of the Earth. Proceedings National Academy of Science 76 9 : — Geodynamics 2 ed. UC Berkeley News. Philosophical Transaction of the Royal Society of London : — Earth and Planetary Science Letters 1. Journal of Geophysical Research Los Alamos National Laboratory.
Online Astronomy eText Table of Contents. University of Hawaii. Contributions to Mineralogy and Petrology 3. Proceedings of the Ocean Drilling Program. Lunar and Planetary Laboratory. Volcano World. Cal Poly Pomona. Planetary Sciences 2nd ed. Minerals: their constitution and origin. The oceans, their physics, chemistry, and general biology. Scripps Institution of Oceanography Archives. June Oceanography 23 2 : — State Hydrological Institute, St. Practical handbook of marine science. Marine science series 3rd ed.
CRC Press. November Resources in Atmospheric Sciences. University of Wyoming. World Book Online Reference Center. University of California, San Diego. Potsdam Institute for Climate Impact Research. University of Illinois. Craig; Orians, Gordon H. Life, the Science of Biology 8th ed. Science Week. Altitude Boundary for Astronautics". Journal of Atmospheric Sciences 31 4 : — Ohio State University. Annual review of earth and planetary sciences 4: — Introduction to Geomagnetic Fields. New York: Cambridge University Press. Kenneth Explanatory Supplement to the Astronomical Almanac.
Archived from the original on Saunders College Publishing. University of Toronto. National Radio Astronomy Observatory. Due to the inverse square law, the radiation at perihelion is about Skeptic Tank. Astronomy and Astrophysics — Kasting Lunar and Planetary Science — Habitable Planets for Man 2nd ed. American Elsevier Publishing Co. New York: Springer-Verlag. American Naturalist 2 : — United Nations. Population Reference Bureau. Hydrology and Earth System Sciences Discussions 4: — Secretariat of the Convention on Biological Diversity. Information Management Group. The Rise and Fall of the Great Powers 1st ed.
Charter Index". The race for space: the United States and the Soviet Union compete for the new frontier. Twenty-First Century Books. Americana Group Publishing. Encyclopedia Astronautica. Random House. July Symbols — Encyclopedia of Western Signs and Ideograms. New York: Ionfox AB. Journal of Geoscience Education 50 2 : — Amherst: Prometheus. Journal of Geoscience Education 53 3 : Annu Rev Genomics Hum Genet 4: — Washington, D. C: National Academies Press. Journal of Research in Science Teaching 43 4 : — Is God a Creationist?
Natural History 2 : 16— American Scientific Affiliation. Buckminster Operating Manual for Spaceship Earth First ed. New York: E. Oxford: Oxford University Press. Discovering the Essential Universe Second ed. National Climatic Data Center. August 20, Each arrow should be read as "within" or "part of". Des continents ou supercontinents se forment puis se divisent. Les principales plaques tectoniques sont : Aire Nom de la Carte totale, en Couvre plaque km2.
Plaque africaine 61,3 Afrique Carte des plaques tectoniques terrestres.
Plaque 47,2 Australie australienne. Plaque Asie et 67,8 eurasienne l'Europe. Position et taille du continent asiatique selon Christophe Colomb. Satellites de la Terre [modifier] Article connexe : Lune. C'est pour cela que les Anciens avaient pu supposer la Terre immobile. Le drapeau non-officiel du Jour de la Terre. Jour de la Terre [modifier] Le Jour de la Terre a lieu le 22 avril, depuis Notes [modifier] 1. VII, trad. L'Islam et son impulsion scientifique originelle, Tiers-Monde, , vol. Enfin, l'imam Abou Hanifah m. Jump to: navigation, search "Primordial soup" redirects here.
For the board game, see Primordial Soup board game. For views on the origins of life outside the natural sciences, see Creation myth. In , William Schopf of UCLA published a paper in the scientific journal Nature arguing that geological formations such as this possess 3. If true, they would be evidence of the earliest known life on earth.
It should not be confused with evolution, which is the study of how groups of already living things change over time, or with cosmogony, which covers how the universe might have arisen. Most amino acids, often called "the building blocks of life", can form via natural chemical reactions unrelated to life, as demonstrated in the Miller—Urey experiment and similar experiments, which involved simulating some of the conditions of the early Earth, in a scientific laboratory. Which of these organic molecules first arose and how they formed the first life is the focus of abiogenesis.
In any theory of abiogenesis, two aspects of life have to be accounted for: replication, and metabolism. The question of which came first gave rise to different types of theories. In the beginning, metabolism-first theories Oparin coacervate were proposed, and only later thinking gave rise to modern, replication-first approach. In modern, still somewhat limited understanding, the first living things on Earth are thought to be single cell prokaryotes which lack a cell nucleus , perhaps evolved from protobionts organic molecules surrounded by a membrane-like structure.
Several hypotheses about early life have been proposed, most notably the iron-sulfur world theory metabolism without genetics and the RNA world hypothesis RNA life-forms. This was paired with heterogenesis, the belief that one form of life derives from a different form e.
According to Aristotle it was a readily observable truth that aphids arise from the dew which falls on plants, fleas from putrid matter, mice from dirty hay, crocodiles from rotting logs at the bottom of bodies of water, and so on. For example, his contemporary, Alexander Ross wrote: "To question this i.
If he doubts of this let him go to Egypt, and there he will find the fields swarming with mice, begot of the mud of Nylus, to the great calamity of the inhabitants. Hooke was followed in by Anton van Leeuwenhoek, who drew and described microorganisms that are now thought to have been protozoa and bacteria. The first solid evidence against spontaneous generation came in from Francesco Redi, who proved that no maggots appeared in meat when flies were prevented from laying eggs. It was gradually shown that, at least in the case of all the higher and readily visible organisms, the previous sentiment regarding spontaneous generation was false.
The alternative seemed to be biogenesis: that every living thing came from a pre-existing living thing omne vivum ex ovo, Latin for "every living thing from an egg". In , Lazzaro Spallanzani demonstrated that microbes were present in the air, and could be killed by boiling. In , Louis Pasteur performed a series of experiments which demonstrated that organisms such as bacteria and fungi do not spontaneously appear in sterile, nutrient-rich media.
Charles Darwin in By the middle of the 19th century, the theory of biogenesis had accumulated so much evidential support, due to the work of Louis Pasteur and others, that the alternative theory of spontaneous generation had been effectively disproven. Pasteur himself remarked, after a definitive finding in , "Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment.
In a letter to Joseph Dalton Hooker on February 1, , Charles Darwin addressed the question, suggesting that the original spark of life may have begun in a "warm little pond, with all sorts of ammonia and phosphoric salts, lights, heat, electricity, etc. He went on to explain that "at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.
Alexander Oparin right at the laboratory. In his The Origin of Life, Oparin proposed that the "spontaneous generation of life" that had been attacked by Louis Pasteur, did in fact occur once, but was now impossible because the conditions found in the early earth had changed, and the presence of living organisms would immediately consume any spontaneously generated organism. Oparin argued that a "primeval soup" of organic molecules could be created in an oxygen-less atmosphere through the action of sunlight.
These would combine in ever-more complex fashions until they formed coacervate droplets. These droplets would "grow" by fusion with other droplets, and "reproduce" through fission into daughter droplets, and so have a primitive metabolism in which those factors which promote "cell integrity" survive, and those that do not become extinct. Many modern theories of the origin of life still take Oparin's ideas as a starting point. Around the same time, J. Haldane suggested that the Earth's pre-biotic oceans—very different from their modern counterparts—would have formed a "hot dilute soup" in which organic compounds could have formed.
This idea was called biopoiesis or biopoesis, the process of living matter evolving from self- replicating but nonliving molecules. This means that oceans and continental crust existed within Ma of Earth's formation. Despite this, the Hadean environment was one highly hazardous to life. Frequent collisions with large objects, up to kilometres mi in diameter, would have been sufficient to vaporise the ocean within a few months of impact, with hot steam mixed with rock vapour leading to high altitude clouds completely covering the planet. After a few months the height of these clouds would have begun to decrease but the cloud base would still have been elevated for about the next thousand years.
After that, it would have begun to rain at low altitude. For another two thousand years rains would slowly have drawn down the height of the clouds, returning the oceans to their original depth only 3, years after the impact event. This would likely have sterilized the planet had life appeared before that time. By examining the time interval between such devastating environmental events, the time interval when life might first have come into existence can be found for different early environments.
The study by Maher and Stevenson shows that if the deep marine hydrothermal setting provides a suitable site for the origin of life, abiogenesis could have happened as early as 4. Work by Leslie Orgel and colleagues on the synthesis of purines has shown that freezing temperatures are advantageous, due to the concentrating effect for key precursors such as HCN. As that new RNA strand grows, it adheres to the template. As an ice crystal forms, it stays pure: only molecules of water join the growing crystal, while impurities like salt or cyanide are excluded.
These impurities become crowded in microscopic pockets of liquid within the ice, and this crowding causes the molecules to collide more often. Evidence of the early appearance of life comes from the Isua supercrustal belt in Western Greenland and from similar formations in the nearby Akilia Islands. These isotopic fingerprints are preserved in the sediments, and Mojzis has used this technique to suggest that life existed on the planet already by 3. Most currently accepted models draw at least some elements from the framework laid out by the Oparin-Haldane hypothesis.
Some theorists suggest that the atmosphere of the early Earth may have been chemically reducing in nature, composed primarily of methane CH4 , ammonia NH3 , water H2O , hydrogen sulfide H2S , carbon dioxide CO2 or carbon monoxide CO , and phosphate PO , with molecular oxygen O2 and ozone O3 either rare or absent. In such a reducing atmosphere, electrical activity can catalyze the creation of certain basic small molecules monomers of life, such as amino acids. This was demonstrated in the Miller—Urey experiment by Stanley L.
Miller and Harold C. Urey in Phospholipids of an appropriate length can spontaneously form lipid bilayers, a basic component of the cell membrane. A fundamental question is about the nature of the first self-replicating molecule. Since replication is accomplished in modern cells through the cooperative action of proteins and nucleic acids, the major schools of thought about how the process originated can be broadly classified as "proteins first" and "nucleic acids first".
The principal thrust of the "nucleic acids first" argument is as follows: 1. The polymerization of nucleotides into random RNA molecules might have resulted in self-replicating ribozymes RNA world hypothesis 2. Selection pressures for catalytic efficiency and diversity might have resulted in ribozymes which catalyse peptidyl transfer hence formation of small proteins , since oligopeptides complex with RNA to form better catalysts. The first ribosome might have been created by such a process, resulting in more prevalent protein synthesis. Synthesized proteins might then outcompete ribozymes in catalytic ability, and therefore become the dominant biopolymer, relegating nucleic acids to their modern use, predominantly as a carrier of genomic information.
As of , no one has yet synthesized a "protocell" using basic components which would have the necessary properties of life the so-called "bottom-up-approach". Without such a proof-of-principle, explanations have tended to be short on specifics. Others have argued that a "top-down approach" is more feasible. One such approach, attempted by Craig Venter and others at The Institute for Genomic Research, involves engineering existing prokaryotic cells with progressively fewer genes, attempting to discern at which point the most minimal requirements for life were reached.
The biologist John Desmond Bernal coined the term Biopoesis for this process, and suggested that there were a number of clearly defined "stages" that could be recognised in explaining the origin of life. Terrestrial origins—organic synthesis driven by impact shocks or by other energy sources such as ultraviolet light or electrical discharges eg. Miller's experiments 2. Extraterrestrial origins—delivery by objects e. The early Earth had a chemically reducing atmosphere, as discussed above.
This atmosphere, exposed to energy in various forms, produced simple organic compounds "monomers". These compounds accumulated in a "soup", which may have been concentrated at various locations Shorelines, oceanic vents etc. By further transformation, more complex organic polymers— and ultimately life— developed in the soup. Other less reducing gases produce a lower yield and variety. It was once thought that appreciable amounts of molecular oxygen were present in the prebiotic atmosphere, which would have essentially prevented the formation of organic molecules; however, the current scientific consensus is that such was not the case.
See Oxygen catastrophe. A graduate student, Stanley Miller, and his professor, Harold Urey, performed an experiment that demonstrated how organic molecules could have spontaneously formed from inorganic precursors, under conditions like those posited by the Oparin-Haldane Hypothesis. The now-famous "Miller—Urey experiment" used a highly reduced mixture of gases—methane, ammonia and hydrogen—to form basic organic monomers, such as amino acids.
The Miller experiment, for example, produces many substances that would undergo cross-reactions with the amino acids or terminate the peptide chain. More fundamentally, it can be argued that the most crucial challenge unanswered by this theory is how the relatively simple organic building blocks polymerise and form more complex structures, interacting in consistent ways to form a protocell. Sustained chemical energy in such systems is derived from redox reactions, in which electron donors, such as molecular hydrogen, react with electron acceptors, such as carbon dioxide see iron-sulfur world theory.
Fox studied the spontaneous formation of peptide structures under conditions that might plausibly have existed early in Earth's history. He demonstrated that amino acids could spontaneously form small peptides. They examined the transient stages between the molecular chaos and a self-replicating hypercycle in a prebiotic soup.
Mathematically treated, hypercycles could create quasispecies, which through natural selection entered into a form of Darwinian evolution. A boost to hypercycle theory was the discovery that RNA, in certain circumstances, forms itself into ribozymes, capable of catalyzing their own chemical reactions.
The hypercycle theory is further degraded since the hypothetical RNA would require the existence of complex biochemicals such as nucleotides which are not formed under the conditions proposed by the Miller—Urey experiment.
Fred Hoyle’s Universe
Hoffmann, a student of Eigen, contributed to the concept of life involving both replication and metabolism emerging from catalytic noise. This is called the stochastic theory of the origin of life. In this theory, he postulated the evolution of bio chemical pathways as fundamentals of the evolution of life.
Moreover, he presented a consistent system of tracing today's biochemistry back to ancestral reactions that provide alternative pathways to the synthesis of organic building blocks from simple gaseous compounds. The energy released from redox reactions of these metal sulfides is not only available for the synthesis of organic molecules, but also for the formation of oligomers and polymers. It is therefore hypothesized that such systems may be able to evolve into autocatalytic sets of self-replicating, metabolically active entities that would predate the life forms known today.
The experiment produced a relatively small yield of dipeptides 0. Radioactive monazite also releases soluble phosphate into regions between sand-grains, making it biologically "accessible". Thus amino acids, sugars and soluble phosphates can all be simultaneously produced, according to Adam. Radioactive actinides, then in greater concentrations, could have formed part of organo-metallic complexes. These complexes could have been important early catalysts to living processes.
John Parnell of the University of Aberdeen suggests that such a process could provide part of the "crucible of life" on any early wet rocky planet, so long as the planet is large enough to have generated a system of plate tectonics which brings radioactive minerals to the surface. As the early Earth is believed to have had many smaller "platelets" it would provide a suitable environment for such processes.
Entropy production is not incidental to the process of life, but rather the fundamental reason for its existence. Present day life augments the entropy production of Earth by catalysing the water cycle through evapotranspiration. It turns out that both RNA and DNA when in water solution are very strong absorbers and extremely rapid dissipaters of ultraviolet light within the nm - nm wavelength range, just that high energy part of the sun's spectrum that could have penetrated the dense prebiotic atmosphere.
Cnossen et al. Absorption and dissipation of UV light by these organic molecules at the Archean ocean surface would have increased significantly the temperature of the surface skin layer leading to enhanced evaporation and thus augmenting the primitive water cycle. Since absorption and dissipation of high energy photons is an entropy producing process, Michaelian argues that non-equilbrium abiogenic synthesis of RNA and DNA utilizing UV light  would have been thermodynamically favored.
The copying process would be repeated during the cool period overnight . Michaelian suggests that traditional origin of life research, expecting to describe the emergence of life from near-equilibrium conditions, is erroneous and that non-equilibrium conditions must be considered, in particular, the importance of entropy production to the emergence of life. Since denaturation would be most probable in the late afternoon when the Archean sea surface temperature would be highest, and since late afternoon sunlight is somewhat circularly polarized, the homochirality of the organic molecules of life can also be explained within the proposed thermodynamic framework.
This is called a racemic mixture. Clark has suggested that homochirality may have started in space, as the studies of the amino acids on the Murchison meteorite showed L-alanine to be more than twice as frequent as its D form, and L-glutamic acid was more than 3 times prevalent than its D counterpart. It is suggested that polarised light has the power to destroy one enantiomer within the proto-planetary disk. Noyes showed that beta decay caused the breakdown of D-leucine, in a racemic mixture, and that the presence of 14C, present in larger amounts in organic chemicals in the early Earth environment, could have been the cause.
Robert M. Hazen reports upon experiments conducted in which various chiral crystal surfaces act as sites for possible concentration and assembly of chiral monomer units into macromolecules. For example Martin and Russel show that physical compartmentation by cell membranes from the environment and self-organization of self-contained redox reactions are the most conserved attributes of living things, and they argue therefore that inorganic matter with such attributes would be life's most likely last common ancestor.
Some of these postulate the early appearance of nucleic acids "genes-first" whereas others postulate the evolution of biochemical reactions and pathways first "metabolism-first". Recently, trends are emerging to create hybrid models that combine aspects of both. This has spurred scientists to try to determine if relatively short RNA molecules could have spontaneously formed that were capable of catalyzing their own continuing replication.
Factors supportive of an important role for RNA in early life include its ability to act both to store information and catalyse chemical reactions as a ribozyme ; its many important roles as an intermediate in the expression and maintenance of the genetic information in the form of DNA in modern organisms; and the ease of chemical synthesis of at least the components of the molecule under conditions approximating the early Earth. Relatively short RNA molecules which can duplicate others have been artificially produced in the lab.
Jack Szostak has shown that certain catalytic RNAs can, indeed, join smaller RNA sequences together, creating the potential, in the right conditions for self-replication. If these were present, Darwinian selection would favour the proliferation of such self-catalysing structures, to which further functionalities could be added. Ribose aminooxazoline can then react with cyanoacetylene in a mild and highly efficient manner to give the alpha cytidine ribonucleotide.
Photoanomerization with UV light allows for inversion about the 1' anomeric centre to give the correct beta stereochemistry. This paper also highlights the possibility for the photo-sanitization of the pyrimidine-2',3'-cyclic phosphates. More abstract and theoretical arguments for the plausibility of the emergence of metabolism without the presence of genes include a mathematical model introduced by Freeman Dyson in the early s and Stuart Kauffman's notion of collectively autocatalytic sets, discussed later in that decade.
For example, instead of the reductive citric acid cycle, the "open" acetyl-CoA pathway another one of the five recognised ways of carbon dioxide fixation in nature today would be compatible with the idea of self-organisation on a metal sulfide surface. The energy source of the thermosynthesis world was thermal cycling, the result of suspension of the protocell in a convection current, as is plausible in a volcanic hot spring; the convection accounts for the self- organization and dissipative structure required in any origin of life model.
The still ubiquitous role of thermal cycling in germination and cell division is considered a relic of primordial thermosynthesis. In the beginning this First Protein also synthesized a library with many proteins, of which only a minute fraction had thermosynthesis capabilities. Just as proposed by Dyson  for the first proteins, the First Protein propagated functionally: it made daughters with similar capabilities, but it did not copy itself.
Functioning daughters consisted of different amino acid sequences. The thermosynthesis world therefore in theory accounts for the origin of the genetic machinery. The RNA World also implies the existence of several enzymes. But even the emergence of a single enzyme by chance is implausible. Winds sweeping across the ocean have a tendency to drive things to shore, much like driftwood collecting on the beach.
It is possible that organic molecules were concentrated on the shorelines in much the same way. Shallow coastal waters also tend to be warmer, further concentrating the molecules through evaporation. While bubbles composed mostly of water burst quickly, water containing amphiphiles forms much more stable bubbles, lending more time to the particular bubble to perform these crucial reactions. Amphiphiles are oily compounds containing a hydrophilic head on one or both ends of a hydrophobic molecule.
Some amphiphiles have the tendency to spontaneously form membranes in water. A spherically closed membrane contains water and is a hypothetical precursor to the modern cell membrane. If a protein would increase the integrity of its parent bubble, that bubble had an advantage, and was placed at the top of the natural selection waiting list. Primitive reproduction can be envisioned when the bubbles burst, releasing the results of the 'experiment' into the surrounding medium.
Once enough of the 'right stuff' was released into the medium, the development of the first prokaryotes, eukaryotes, and multicellular organisms could be achieved. But they are not a likely precursor to the modern cell membrane, as cell membranes are composed primarily of lipid compounds rather than amino-acid compounds for types of membrane spheres associated with abiogenesis, see protobionts, micelle, coacervate.
A recent model by Fernando and Rowe suggests that the enclosure of an autocatalytic non- enzymatic metabolism within protocells may have been one way of avoiding the side-reaction problem that is typical of metabolism first models. Autocatalysts are substances which catalyze the production of themselves, and therefore have the property of being a simple molecular replicator. In his book, Dawkins cites experiments performed by Julius Rebek and his colleagues at the Scripps Research Institute in California in which they combined amino adenosine and pentafluorophenyl ester with the autocatalyst amino adenosine triacid ester AATE.
One system from the experiment contained variants of AATE which catalysed the synthesis of themselves. This experiment demonstrated the possibility that autocatalysts could exhibit competition within a population of entities with heredity, which could be interpreted as a rudimentary form of natural selection. Graham Cairns-Smith of the University of Glasgow in and explored as a plausible illustration by several other scientists, including Richard Dawkins.
Clay theory postulates that complex organic molecules arose gradually on a pre- existing, non-organic replication platform—silicate crystals in solution. Complexity in companion molecules developed as a function of selection pressures on types of clay crystal is then exapted to serve the replication of organic molecules independently of their silicate "launch stage". Cairns-Smith is a staunch critic of other models of chemical evolution.
In , Kahr and colleagues reported their experiments to examine the idea that crystals can act as a source of transferable information, using crystals of potassium hydrogen phthalate. They then examined the distribution of imperfections in the crystal system and found that the imperfections in the mother crystals were indeed reproduced in the daughters. The daughter crystals had many additional imperfections. For a gene-like behavior the additional imperfections should be much less than the parent ones, thus Kahr concludes that the crystals "were not faithful enough to store and transfer information from one generation to the next".
It is now reasonably well established that microbial life is plentiful at shallow depths in the Earth, up to 5 kilometres 3. It is claimed that discovery of microbial life below the surface of another body in our solar system would lend significant credence to this theory. Thomas Gold also asserted that a trickle of food from a deep, unreachable, source is needed for survival because life arising in a puddle of organic material is likely to consume all of its food and become extinct.
Gold's theory is that flow of food is due to out-gassing of primordial methane from the Earth's mantle; more conventional explanations of the food supply of deep microbes away from sedimentary carbon compounds is that the organisms subsist on hydrogen released by an interaction between water and reduced iron compounds in rocks. Note that exogenesis is related to, but not the same as, the notion of panspermia. A supporter of this theory was Francis Crick. Organic compounds are relatively common in space, especially in the outer solar system where volatiles are not evaporated by solar heating.
It is supposed that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth. An alternative but related hypothesis, proposed to explain the presence of life on Earth so soon after the planet had cooled down, with apparently very little time for prebiotic evolution, is that life formed first on early Mars. Due to its smaller size Mars cooled before Earth a difference of hundreds of millions of years , allowing prebiotic processes there while Earth was still too hot. Life was then transported to the cooled Earth when crustal material was blasted off Mars by asteroid and comet impacts.
Mars continued to cool faster and eventually became hostile to the continued evolution or even existence of life it lost its atmosphere due to low volcanism ; Earth is following the same fate as Mars, but at a slower rate. Neither hypothesis actually answers the question of how life first originated, but merely shifts it to another planet or a comet.
Evidence to support the plausibility of the concept is scant, but it finds support in recent study of Martian meteorites found in Antarctica and in studies of extremophile microbes. This combination yielded large amounts of organic material that self-organised to form bubbles or micelles when immersed in water. Dworkin considered these bubbles to resemble cell membranes that enclose and concentrate the chemistry of life, separating their interior from the outside world.
The bubbles produced in these experiments were between 10 to 40 micrometres 0. Remarkably, the bubbles fluoresced, or glowed, when exposed to UV light. Absorbing UV and converting it into visible light in this way was considered one possible way of providing energy to a primitive cell. Such fluorescence also provides the benefit of acting as a sunscreen, diffusing any damage that otherwise would be inflicted by UV radiation.
Such a protective function would have been vital for life on the early Earth, since the ozone layer, which blocks out the sun's most destructive UV rays, did not form until after photosynthetic life began to produce oxygen. In it was announced by NASA that scientists have identified one of the fundamental chemical buildings blocks of life in a comet for the first time: glycine, an amino acid, was detected in the material ejected from Comet Wild-2 in and grabbed by NASA's Stardust probe. Tiny grains, just a few thousandths of a millimetre in size, were collected from the comet and returned to Earth in in a sealed capsule, and distributed among the world's leading astro-biology labs.
NASA said in a statement that it took some time for the investigating team, led by Dr Jamie Elsila, to convince itself that the glycine signature found in Stardust's sample bay was genuine and not just Earthly contamination. Glycine has been detected in meteorites before and there are also observations in interstellar gas clouds claimed for telescopes, but the Stardust find is described as a first in cometary material. It is known that prior to the emergence of life on Earth, the early solar system's planets were regularly bombarded by comets. Carl Pilcher, who leads NASA's Astrobiology Institute commented that "The discovery of glycine in a comet supports the idea that the fundamental building blocks of life are prevalent in space, and strengthens the argument that life in the Universe may be common rather than rare.
These molecules were not present on early Earth, however other amphiphilic long chain molecules also form membranes. Furthermore, these bodies may expand by insertion of additional lipids , and under excessive expansion may undergo spontaneous splitting which preserves the same size and composition of lipids in the two progenies.
The main idea in this theory is that the molecular composition of the lipid bodies is the preliminary way for information storage, and evolution led to the appearance of polymer entities such as RNA or DNA that may store information favorably. Still, no biochemical mechanism has been offered to support the Lipid World theory. What has been missing is some force that drives polymerization.
The resolution of this problem may well be in the properties of polyphosphates. Several mechanisms for such polymerization have been suggested. Polyphosphates cause polymerization of amino acids into peptides. They are also logical precursors in the synthesis of such key biochemical compounds as ATP.
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A key issue seems to be that calcium reacts with soluble phosphate to form insoluble calcium phosphate apatite , so some plausible mechanism must be found to keep calcium ions from causing precipitation of phosphate. There has been much work on this topic over the years, but an interesting new idea is that meteorites may have introduced reactive phosphorus species on the early Earth. For example, from spectral analyses, organic molecules are known to be present in comets and meteorites.
In , a team detected traces of polycyclic aromatic hydrocarbons PAH's in a nebula. In the disk of material surrounding the star, there is a very large range of molecules, including cyanide compounds, hydrocarbons, and carbon monoxide. PAHs have also been found all over the surface of galaxy M81, which is 12 million light years away from the Earth, confirming their widespread distribution in space. Hartman for example combines a number of theories together, by proposing that: The first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic and other dicarboxylic acids.
This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hotspring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids. If biosynthesis recapitulates biopoesis, then the synthesis of amino acids preceded the synthesis of the purine and pyrimidine bases. Furthermore the polymerization of the amino acid thioesters into polypeptides preceded the directed polymerization of amino acid esters by polynucleotides.
Lynn Margulis's endosymbiotic theory suggests that multiple forms of bacteria entered into symbiotic relationship to form the eukaryotic cell. The horizontal transfer of genetic material between bacteria promotes such symbiotic relationships, and thus many separate organisms may have contributed to building what has been recognised as the Last Universal Common Ancestor LUCA of modern organisms. James Lovelock's Gaia theory, proposes that such bacterial symbiosis establishes the environment as a system produced by and supportive of life. His arguments strongly weaken the case for life having evolved elsewhere in the solar system.
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London: John Murray. Volume 3. The Origin of Life. New York: Dover. Origins of Life. London: Wiedenfeld and Nicholson. A short history of nearly everything. London: Black Swan. Aquatic Geochemistry 4: — Nature : —4. Origins of Life and Evolution of Biospheres —9. Icarus 2 : — Origins of Life and Evolution of the Biosphere 35 5 : — Nature : 55—9. Journal of Molecular Evolution 39 6 : — Proceedings of the Physical Society.
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Astrobiology Magazine. B : 59— Direct 1: Otroshchenkob and Salvatore Santoli Biosystems 42 2—3 : — J Theor Biol 4 : — June 4, January 8, At that moment, the long journey of study and research began which would ultimately lead Maria to present her own work in many countries: Japan, Mexico, Egypt, Colombia, France and Tunisia. Interested in the theme of motherhood, she recognized in that discipline an effective compendium of Belly Dancing - particularly with respect to breathing techniques - and became the first teacher in Italy to teach a fusion of the two as preparation for childbirth.
She has produced a variety of teaching DVDs, and wrote and directed Searching for Scheherazade, the first documentary in Italy on the art of belly dancing and the daily efforts to keep the dance alive. She currently teaches at the IALS in Rome and has the Omphalos Cultural Center and the Breath Theatre, based in Fiano Romano Rome , where she develops new talent, in collaboration with other teachers, through the search for a Belly Dance adapted to theatre and choreographic experimentation.
See All Customer Reviews. Shop Books. Add to Wishlist. USD Sign in to Purchase Instantly. Overview Bellydance is incredibly popular today, but many prejudices remain about this art because it is not understood deeply enough. Product Details About the Author. About the Author Maria Strova was born in Colombia, where she began to study classic Russian dance at the age of Show More. Average Review. Write a Review. Related Searches. Anemia: Ricette curative e consigli alimentari.
Ti senti spesso stanco? Hai un problema di tachicardia? Fai fatica a concentrarti? Il tuo Le tue unghie sono fragili? In questa View Product. Elio il libro sull'essiccazione. Provate a lasciare qualcosa di organico da qualche parte, un pezzo di mela, qualche foglia Provate a lasciare qualcosa di organico da qualche parte, un pezzo di mela, qualche foglia di insalata, un limone, uno spicchio d'aglio o qualsiasi altra cosa biodegradabile, non importa dove, ed osservatelo per alcuni giorni, noterete che tutti quanti tendono Emozioni: Ricette artistiche vegan.
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