Fuyan Cave ( Chinese : 福岩洞 ) is a complex of limestone caves in Tangbei village, Lefutang town, Daoxian , Hunan province, south central China famous for the discovery of the oldest evidence for unambiguously fully modern humans outside Africa. 47 human teeth, dating to between 80,000 and 120,000 years ago, were discovered at Fuyan Cave. The teeth are also unusual for showing signs of cavities , a feature typically not found in teeth older than 50,000 years. However, a later study focusing on autosomal DNA analysis of the remains challenged this assertion, and found that the remains were younger than previously suspected.
42-527: Fuyan consists of three caves connected by tunnels. The cave system has a volume of 3,000 m (110,000 cu ft) and ranges over 3 km (1.2 sq mi). Fuyan Cave was discovered in 1984. The cave is located at latitude 25°39′02.7″N, longitude 111°28′49.2″E, at 232 m above sea level. The cave was excavated in 2011 over an area of 20 m (220 sq ft). The 2011 excavation revealed 5 hominin teeth and fossil remains from 39 different mammalians species, including some extinct ones. The cave
84-409: A calcium bicarbonate solution in caverns. The partial pressure of carbon dioxide in the water must be greater than the partial pressure of carbon dioxide in the cave chamber for conventional stalagmite growth. If stalactites – the ceiling formations – grow long enough to connect with stalagmites on the floor, they form a column. To preserve Stalagmites, it should normally not be touched, since
126-516: A solvation shell (or hydration shell in the case of water) around each particle of solute. The solvent molecules in the immediate vicinity of a solute particle often have a much different ordering than the rest of the solvent, and this area of differently ordered solvent molecules is called the cybotactic region. Water is the most common and well-studied polar solvent, but others exist, such as ethanol , methanol , acetone , acetonitrile , and dimethyl sulfoxide . Polar solvents are often found to have
168-462: A cave is a stalactite . The most common stalagmites are speleothems , which usually form in limestone caves. Stalagmite formation occurs only under certain pH conditions within the cavern. They form through deposition of calcium carbonate and other minerals, which is precipitated from mineralized water solutions . Limestone is the chief form of calcium carbonate rock , which is dissolved by water that contains carbon dioxide , forming
210-438: A cavity must form in the solvent to make space for a solute. This is both entropically and enthalpically unfavorable, as solvent ordering increases and solvent-solvent interactions decrease. Stronger interactions among solvent molecules leads to a greater enthalpic penalty for cavity formation. Next, a particle of solute must separate from the bulk. This is enthalpically unfavorable since solute-solute interactions decrease, but when
252-409: A favorable change in the interactions between the protein and the surrounding water molecules. Folded proteins are stabilized by 5-10 kcal/mol relative to the unfolded state due to a combination of solvation and the stronger intramolecular interactions in the folded protein structure , including hydrogen bonding . Minimizing the number of hydrophobic side chains exposed to water by burying them in
294-558: A high dielectric constant , although other solvent scales are also used to classify solvent polarity. Polar solvents can be used to dissolve inorganic or ionic compounds such as salts. The conductivity of a solution depends on the solvation of its ions. Nonpolar solvents cannot solvate ions, and ions will be found as ion pairs. Hydrogen bonding among solvent and solute molecules depends on the ability of each to accept H-bonds, donate H-bonds, or both. Solvents that can donate H-bonds are referred to as protic, while solvents that do not contain
336-442: A matter of hours, days, or weeks, whereas limestone stalagmites may take up to thousands or hundred thousands of years. A key difference with lava stalagmites is that once the molten lava has ceased flowing, so too will the stalagmites cease to grow. This means that if the lava stalagmites were to be broken, they would never grow back. Stalagmites in lava tubes are rarer than their stalactite counterparts because during their formation,
378-411: A member of') is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from ceiling drippings. Stalagmites are typically composed of calcium carbonate , but may consist of lava , mud , peat , pitch , sand , sinter , and amberat (crystallized urine of pack rats ). The corresponding formation hanging down from the ceiling of
420-598: A polarized bond to a hydrogen atom and cannot donate a hydrogen bond are called aprotic. H-bond donor ability is classified on a scale (α). Protic solvents can solvate solutes that can accept hydrogen bonds. Similarly, solvents that can accept a hydrogen bond can solvate H-bond-donating solutes. The hydrogen bond acceptor ability of a solvent is classified on a scale (β). Solvents such as water can both donate and accept hydrogen bonds, making them excellent at solvating solutes that can donate or accept (or both) H-bonds. Some chemical compounds experience solvatochromism , which
462-414: A solute by water is called hydration. Solubility of solid compounds depends on a competition between lattice energy and solvation, including entropy effects related to changes in the solvent structure. By an IUPAC definition, solvation is an interaction of a solute with the solvent , which leads to stabilization of the solute species in the solution . In the solvated state, an ion or molecule in
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#1732757983950504-416: A solution is surrounded or complexed by solvent molecules. Solvated species can often be described by coordination number , and the complex stability constants . The concept of the solvation interaction can also be applied to an insoluble material, for example, solvation of functional groups on a surface of ion-exchange resin . Solvation is, in concept, distinct from solubility . Solvation or dissolution
546-507: Is a kinetic process and is quantified by its rate. Solubility quantifies the dynamic equilibrium state achieved when the rate of dissolution equals the rate of precipitation . The consideration of the units makes the distinction clearer. The typical unit for dissolution rate is mol/s. The units for solubility express a concentration: mass per volume (mg/mL), molarity (mol/L), etc. Solvation involves different types of intermolecular interactions: Which of these forces are at play depends on
588-457: Is a change in color due to solvent polarity. This phenomenon illustrates how different solvents interact differently with the same solute. Other solvent effects include conformational or isomeric preferences and changes in the acidity of a solute. The solvation process will be thermodynamically favored only if the overall Gibbs energy of the solution is decreased, compared to the Gibbs energy of
630-546: Is apparent that they are not solvated. Strong solvent–solute interactions make the process of solvation more favorable. One way to compare how favorable the dissolution of a solute is in different solvents is to consider the free energy of transfer. The free energy of transfer quantifies the free energy difference between dilute solutions of a solute in two different solvents. This value essentially allows for comparison of solvation energies without including solute-solute interactions. In general, thermodynamic analysis of solutions
672-407: Is done by modeling them as reactions. For example, if you add sodium chloride to water, the salt will dissociate into the ions sodium(+aq) and chloride(-aq). The equilibrium constant for this dissociation can be predicted by the change in Gibbs energy of this reaction. The Born equation is used to estimate Gibbs free energy of solvation of a gaseous ion. Recent simulation studies have shown that
714-417: Is due to favorable van der Waals interactions and intramolecular electrostatic interactions which would be dampened in the presence of a solvent. As computer power increased, it became possible to try and incorporate the effects of solvation within a simulation and the simplest way to do this is to surround the molecule being simulated with a "skin" of solvent molecules, akin to simulating the molecule within
756-452: Is necessary to release an ion from its lattice and the energy given off when it combines with a solvent molecule is called the enthalpy change of solution . A negative value for the enthalpy change of solution corresponds to an ion that is likely to dissolve, whereas a high positive value means that solvation will not occur. It is possible that an ion will dissolve even if it has a positive enthalpy value. The extra energy required comes from
798-459: Is still active inside. Their mineralogical composition, close to that of siliceous minerals commonly found in basalt (for example, obsidian ), the main constituent of volcanic glass , is different. Their mechanism of formation/crystallization is also notably different from that of limestone stalagmites ( CaCO 3 ) but the common point is that it remains driven by gravity. Drops of molten lava (siliceous material, SiO 2 ) solidify onto
840-624: Is the change in enthalpy minus the product of temperature (in Kelvin ) times the change in entropy. Gases have a negative entropy of solution, due to the decrease in gaseous volume as gas dissolves. Since their enthalpy of solution does not decrease too much with temperature, and their entropy of solution is negative and does not vary appreciably with temperature, most gases are less soluble at higher temperatures. Enthalpy of solvation can help explain why solvation occurs with some ionic lattices but not with others. The difference in energy between that which
882-456: The Holocene , although these recent findings are still under review. Specimen number FY-HT2 (9380±90 BP) in new study was incorrect identified as human teeth. Reconstructions of “deer-like” wear bear no resemblance to the pres-ervational reality of the tooth FY-HT-2. The discovery is important for many reasons. Previous to this discovery, the earliest evidence for fully modern humans outside
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#1732757983950924-502: The surface will penetrate into a cave and if temperatures are below freezing temperature, the water will collect on the floor into stalagmites. Deposition may also occur directly from the freezing of water vapor . Similar to lava stalagmites, ice stalagmites form very quickly within hours or days. Unlike lava stalagmites however, they may grow back as long as water and temperatures are suitable. Ice stalagmites are more common than their stalactite counterparts because warmer air rises to
966-520: The Arabian Peninsula ( Tianyuan Cave , Niah Cave , Mungo Man ) dates to around 40,000 to 50,000 years, so the discovery at Fuyan Cave provides evidence showing that humans migrated out of Africa a lot earlier than previously assumed. Secondly, the finds at Fuyan Cave are much closer to modern humans than they are to contemporary finds at Xujiayao and Qafzeh . Thirdly, the discovery shows that modern humans arrived in southern China when there
1008-471: The attractive forces holding the solute particles together, the solvent particles pull the solute particles apart and surround them. The surrounded solute particles then move away from the solid solute and out into the solution. Ions are surrounded by a concentric shell of solvent . Solvation is the process of reorganizing solvent and solute molecules into solvation complexes and involves bond formation, hydrogen bonding , and van der Waals forces . Solvation of
1050-407: The ceilings of caves and may raise temperatures to above freezing. Ice stalactites may also form corresponding stalagmites below them, and given time, may grow together to form an ice column. Stalactites and stalagmites can also form on concrete ceilings and floors, although they form much more rapidly there than in the natural cave environment. The secondary deposits derived from concrete are
1092-399: The center of a folded protein is a driving force related to solvation. Solvation also affects host–guest complexation . Many host molecules have a hydrophobic pore that readily encapsulates a hydrophobic guest. These interactions can be used in applications such as drug delivery, such that a hydrophobic drug molecule can be delivered in a biological system without needing to covalently modify
1134-438: The chemical reactions to deposit calcium carbonate as a stalagmite. These stalagmites rarely grow taller than a few centimetres. Secondary deposits, which create stalagmites, stalactites, flowstone etc., outside the natural cave environment, are referred to as " calthemites ". These concrete derived secondary deposits cannot be referred to as " speleothems " due to the definition of the word. The largest known stalagmite in
1176-442: The dripping molten material most often falls onto still-moving lava flow which absorbs or carries the material away. The generic term "lavacicle" has been applied to lava stalactites and stalagmites indiscriminately, and evolved from the word "icicle". A common stalagmite found seasonally or year round in many caves is the ice stalagmite, commonly referred to as icicles , especially in above-ground contexts. Water seepage from
1218-581: The drug in order to solubilize it. Binding constants for host–guest complexes depend on the polarity of the solvent. Hydration affects electronic and vibrational properties of biomolecules. Due to the importance of the effects of solvation on the structure of macromolecules, early computer simulations which attempted to model their behaviors without including the effects of solvent ( in vacuo ) could yield poor results when compared with experimental data obtained in solution. Small molecules may also adopt more compact conformations when simulated in vacuo ; this
1260-544: The floor of the already emptied lava tube, when the lava temperature sufficiently decreases after the passage and the complete purge of the main lava flow. Essentially, it is still the gravity deposition of material onto the floor of a cave (or a void). However the difference from calcareous stalagmites is that the transport of siliceous material occurs in the molten state and not dissolved in aqueous solution; CO 2 degassing does not play any significant role. With lava stalagmites, their formation also happens very quickly in only
1302-594: The increase in entropy that results when the ion dissolves. The introduction of entropy makes it harder to determine by calculation alone whether a substance will dissolve or not. A quantitative measure for solvation power of solvents is given by donor numbers . Although early thinking was that a higher ratio of a cation's ion charge to ionic radius , or the charge density, resulted in more solvation, this does not stand up to scrutiny for ions like iron(III) or lanthanides and actinides , which are readily hydrolyzed to form insoluble (hydrous) oxides. As these are solids, it
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1344-439: The interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the solute, including solubility, reactivity, and color, as well as influencing the properties of the solvent such as its viscosity and density. If the attractive forces between the solvent and solute particles are greater than
1386-459: The molecular structure and properties of the solvent and solute. The similarity or complementary character of these properties between solvent and solute determines how well a solute can be solvated by a particular solvent. Solvent polarity is the most important factor in determining how well it solvates a particular solute. Polar solvents have molecular dipoles, meaning that part of the solvent molecule has more electron density than another part of
1428-409: The molecule. The part with more electron density will experience a partial negative charge while the part with less electron density will experience a partial positive charge. Polar solvent molecules can solvate polar solutes and ions because they can orient the appropriate partially charged portion of the molecule towards the solute through electrostatic attraction. This stabilizes the system and creates
1470-444: The result of concrete degradation, where calcium ions are leached out of the concrete in solution and redeposited on the underside of a concrete structure to form stalactites and stalagmites. Calcium carbonate deposition as a stalagmite occurs when the solution carries the calcium laden leachate solution to the ground under the concrete structure. Carbon dioxide is absorbed into the alkaline leachate solution, which facilitates
1512-426: The rock buildup is formed by minerals precipitating out of the water solution onto the existing surface; skin oils can alter the surface tension where the mineral water clings or flows, thus affecting the growth of the formation. Oils and dirt (mud, clay) from human contact can also stain the formation and change its color permanently. Another type of stalagmite is formed in lava tubes while molten and fluid lava
1554-435: The separated solvent and solid (or gas or liquid). This means that the change in enthalpy minus the change in entropy (multiplied by the absolute temperature) is a negative value, or that the Gibbs energy of the system decreases. A negative Gibbs energy indicates a spontaneous process but does not provide information about the rate of dissolution. Solvation involves multiple steps with different energy consequences. First,
1596-474: The solute particle enters the cavity, the resulting solvent-solute interactions are enthalpically favorable. Finally, as solute mixes into solvent, there is an entropy gain. [REDACTED] The enthalpy of solution is the solution enthalpy minus the enthalpy of the separate systems, whereas the entropy of solution is the corresponding difference in entropy . The solvation energy (change in Gibbs free energy )
1638-593: The variation in solvation energy between the ions and the surrounding water molecules underlies the mechanism of the Hofmeister series . Solvation (specifically, hydration ) is important for many biological structures and processes. For instance, solvation of ions and/or of charged macromolecules, like DNA and proteins, in aqueous solutions influences the formation of heterogeneous assemblies, which may be responsible for biological function. As another example, protein folding occurs spontaneously, in part because of
1680-715: The world exceeds 70 metres (230 ft) in height and is in Sơn Đoòng Cave , Vietnam . In the Zagros Mountains of south Iran, approximately 6 km (3.7 miles) from the ancient city of Bishapur , in the Shapur cave on the fourth of five terraces stands the 3rd-century colossal statue of Shapur I , second ruler of the Sassanid Empire . The statue, carved from one stalagmite, is nearly 7 m (23 ft) high. Dissolution (chemistry) Solvation describes
1722-792: Was an older, more primitive hominin present in northern China. Lastly, the discovery shows that modern humans were present in Asia at a time when there is no evidence for fully modern humans in Europe (43,000 BC), which is perhaps explained by the presence of Neanderthals in Europe preventing the entry of the modern humans. Stalagmites A stalagmite ( UK : / ˈ s t æ l ə ɡ ˌ m aɪ t / , US : / s t ə ˈ l æ ɡ m aɪ t / ; from Greek σταλαγμίτης ( stalagmítēs ) ; from Ancient Greek σταλαγμίας ( stalagmías ) 'dropping, trickling' and -ίτης ( -ítēs ) 'one connected to,
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1764-409: Was excavated in 2011 and in 2013. The teeth were all discovered in the middle cave. The teeth were dated by dating nearby stalagmites . The stalagmites were dated to at least 80,000 years. Since the teeth were found under rock over which the stalagmites had grown, the teeth must be older than 80,000 years old. More recent ancient DNA analysis of these remains indicated that the remains dated instead to
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