Why are earth life-forms carbon based and not silicon based? both are very similar on the periodic table.?
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While similar to carbon, silicon does not form double bonds in the way that carbon does. Nor does it form extensive ring compounds. This is ultimately due to the fact that carbon is smaller and more electronegative than silicon. The only way that silicon form complex structures is in conjunction with oxygen and even then, it is more limited than carbon. So it is unlikely that the complexities required for life would be possible for silicon based chemistry. Too bad....
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Go here, it has an easy to read chart on composition. Most asteroids are carbon based. Asteroids with iron in them usually also have lots of silica.\n\nhttp://jade.ccccd.edu/jwilson/asteroids.html
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People useally know that Carbon exist in forms of graphite and diamond. graphite and diamond are the two naturally occuring forms of carbon.  However back in 1985, Robert Curl, Harold Kroto and Richard Smalley, were able to create third allotrope of carbon, Buckminsterfullerenes also known as Buckyball using Using laser evaporation of graphite!  The structure of C60 is a truncated icosahedron, which resembles a round soccer ball of the type made of hexagons and pentagons, with a carbon atom at the corners of each hexagon and a bond along each edge.\n\nSince its invention/discovery, much research has been done to create more allotropes of carbon.  The nano technology you hear today has its roots in discovery and concepts of buckyball.
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Origin of Life\nBacteria appeared on earth between 3.4 and 4 billion years ago. Precambrian evidence of filamentous bacteria-like structures, found making up fossilized sediments called stromalites, has been discovered in Australia and southern Africa. These fossils date back between 3.4 and 3.5 billion years old. Environmental conditions of earth 4 billion years ago were much different than those of today. It has been theorized that the atmosphere was a reducing atmosphere with intense lightning, tremendous volcanic activity, very little oxygen, intense ultraviolet radiation, and meteorite bombardment. These conditions made it impossible for any type of aerobic life to exist. The first cells may have originated by chemical evolution in an anaerobic environment.\n\nAbiotic Synthesis Theory of Life: A.I.Oparin postulated, in the 1920's, that primitive earth with its reducing atmosphere favored chemical reactions that produced simple monomers that eventually formed complex organic compounds necessary for life. Stanley Miller and Harold Urey tested this hypothesis by building an apparatus to simulate the conditions of the earth at that time.\n\n \n\n\n \n\nTheir experiments produced 20 amino acids and other organic compounds including: ATP, lipids, some sugars, and the bases of RNA and DNA. The main problem of organic synthesis is how did these molecules develop without the aid of enzymes to speed up the reactions? Sidney Fox, of the University of Miami, dripped a dilute solution of organic monomers onto hot sand, clay , and rock. The water vaporized and left behind polypeptides he called proteinoids. Clay was abundant in prebiotic earth. Clay has the ability to act as a substrate for this type of chemical reaction. The charged sites on the clay attracted monomers in such concentrations to bring them into close proximity for chemical binding. Once these organic compounds were produced, aggregates of these proteinoids self-assembled into small spheres called protobionts. These small spheres were capable of osmotic swelling and shrinking and even able to produce a membrane potential.\n\nRNA the first Genetic Material: Evidence to support the idea that RNA was the first genetic material includes: short polymers of self-replicating RNA have been abiotically produced in a test tube without enzymes. RNA has the ability to act as a catalyst to help make mRNA, tRNA or rRNA. The RNA folding is unique depending on its sequence. This along with mutations, creates a variety of closely related molecules. Through chance this self-replicating material was captured by the protobionts and the entire structure developed under the guide of natural selection.\n\nOther Origin Theories:\n\nPanspermia. Extraterrestrial organic compounds located on the surface of meteorites could well have contributed to the pool of material found on prebiotic earth. Modern meteorites have given up specimens of simple organic compounds such as amino acids.\n\nSome researchers believe that life began on the sea floor away from the harsh surface environments. The discovery of deep sea vents showed the scientific community that the materials needed for life to begin were present away from the harsh surface.\n\nJulius Rebek produced a simple organic molecule in 1991 that served as a template for self-replication. This discovery suggests that RNA was too complex to have come first and a much simpler self-replicating molecule preceded it.
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Diamond is carbon in its most concentrated form. Except for trace impurities like boron and nitrogen, diamond is composed solely of carbon, the chemical element that is fundamental to all life.\n\nBut diamond is distinctly different from its close cousins the common mineral graphite and lonsdaleite, both of which are also composed of carbon. Why is diamond the hardest surface known while graphite is exceedingly soft? Why is diamond transparent while graphite is opaque and metallic black? What is it that makes diamond so unique? \n\nThe key to these questions lie in diamond's particular arrangement of carbon atoms or its crystal structure--the feature that defines any mineral's fundamental properties. A crystal is a solid body formed from the bonding of atomic elements or compounds in a repeating arrangement. Often, crystals possess smooth external faces. Due to their symmetrical and finite nature, the building blocks of crystals are limited to relatively small numbers of atoms, and their chemical compositions to simple numerical combinations of elements.\n\nA neutral carbon atom has 6 protons and 6 electrons surrounding its nucleus. Four of the electrons in a carbon atom are valence electrons, which are electrons that are available to form bonds with other atoms. In graphite, each carbon atom bonds only 3 of its 4 valence electrons with neighboring carbons. The resulting structure of these bonds is a flat sheet of connected carbon atoms. Though individually strong, these layers are only weakly connected to one another, and the ease with which they are separated is what makes graphite so slippery.\n \nIn diamond however, every carbon shares all 4 of its available electrons with adjacent carbon atoms, forming a tetrahedral unit. This shared electron-pair bonding forms the strongest known chemical linkage, the covalent bond, which is responsible for many of diamond's superlative properties. The repeating structural unit of diamond consists of 8 atoms which are fundamentally arranged in a cube.\n\nUsing this cubic form and its highly symmetrical arrangement of atoms, diamond crystals can develop in a variety of different shapes known as "crystal habits." The octahedron, or eight-sided shape that we associate with diamonds is its most common crystal habit. But diamond crystals can also form cubes, dodecahedra, and even combinations of these shapes. All of these shapes are manifestations of the cubic crystal system to which the mineral diamond belongs. Two exceptions are the flat form called a macle, which is actually a composite crystal, and etched crystals, which have rounded surfaces and, sometimes, elongated shapes.\n\nReal diamond crystals don't have completely smooth faces. Trigons are triangular growths that reflect subtle changes in height on a diamond's face. The trigons shown here are slight indentations that were most likely produced by a natural etching of the crystal. However, raised trigons, which point in the same direction as the crystal face, may also occur from etching, dissolution, or as part of the natural growth of the crystal.\n\nDiamond is renowned for its hardness. Hardness is the measure of a substance's resistance to being scratched, and only a diamond can scratch another diamond. Diamond is the hardest substance known.\n\nHardness is not the only measure of a mineral's durability--the relative resistance to fracture is another. Although diamond is not fragile or prone to breaking apart, all substances including diamond can fracture or shatter. Due to its particular crystal structure, diamond has certain planes of weakness along which it can be split. Diamond is said to have perfect cleavage in four different directions, meaning it will separate neatly along these lines rather than in a jagged or irregular fashion. This is because the diamond crystal has fewer chemical bonds along the plane of its octahedral face than in other directions. Diamond cutters take advantage
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Carbon occurs in all organic life and is the basis of organic chemistry. This nonmetal also has the interesting chemical property of being able to bond with itself and a wide variety of other elements, forming nearly ten million known compounds. \n\nBecause of their unique properties, multi-carbon compounds exhibit extremely large variety and the range of application of organic compounds is enormous. They form the basis of or are important constituents of many products (paints, plastics, food, explosives, drugs, petrochemicals, and many others) and of course (apart from a very few exceptions) they form the basis of all life processes.\n\nThe different shapes and chemical reactivities of organic molecules provide an astonishing variety of functions, like those of enzyme catalysts in biochemical reactions of live systems. The autopropagating nature of these is what life is all about.\n\nBecause of the special properties of carbon, it is likely that life on other star systems will be found to be carbon-based, in spite of speculations about the possibility of substituting silicon, which lies just below carbon in the periodic table.
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YES.\n\nSilicon does not polymerize very well.  Every human being on the planet would be a walking miracle.\n\nThat's NOT, however, to say that silicon based life is impossible, just that it would be markedly different from any we know.
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non carbon-based life would be too different from life on earth. a DNA molecule constructed from a Si backbone instead of C would be too heavy and too large to function properly.\n\ncarbon is basically one of the more unique elements on the table, being small and reactive (as opposed to silicon or other group iv's). it can form bonds with itself or many other atoms. this property is responsible for literally millions of chemical compounds(most compounds on earth contain carbon) known to man.\n\ncarbon bonds with oxygen to form carbon dioxide, necessary for the life. silicon dioxide on the other hand, is completely different. SiO2 is sand.\n\nyou could compare carbon with say, water, which is also one of the weirdest compounds known to scientists. yet carbon and water are necessary for all life. i would say that the most interesting elements are the most necessary. silicon is just too normal...
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graphite and diamond are allotropes of carbon.This is one of the unique properties of carbon.
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Life exists almost everywhere on earth, and it has many forms.  Some of which are almost impossible to detect and it's debated whether they're actually "life" (like virii).\n\nIf it could be proven either way, I would bet my worldly posessions and my right arm that there is some sort of life beyond Earth.  They might not be carbon-based or water-based, but I am certain that there are objects out there that consume things, grow, reproduce, and possibly defend themselves or even have rational consciousness.\n\nAs for some alien being looking just like a human and living among us, that's a different story.  I can't see two independent strains of life coming out so similar, especially considering the variety right here on our little planet.  Either we'd all be from alien roots, or the "aliens" would have originated from earthly roots.
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carbon is tetravalent (ie it is able to form bonds with 4 other atoms. It therefore can form backbones of more complex structures (see diamond and graphite). It is also found abundantly on earth.
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as humans we are carbon based but in order to live we need Oxygen\n\nYeah I think there are millions of things out there living on other gases.
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The table is of the elements.  Carbon dioxide is not an element.
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Well.. \nI'm more scientific than religious in this matter. \nThe reason Earth has life is because of the certain climate, temperature, etc. which is perfect for life. \nHowever, there are always news stories about "possible life on mars" and as such. And I believe that for life to form, there needs to be a certain set conditions which allow life to be formed and which support and maintain it. \n\nTherefore,  most definitely there could have been life in other planets, maybe some organisms or something else which is suited to that planet's climate, temp. and etc. It could be that we either can not detect that life on the other planets or the planet is undergoing some sort of climatic change which does not support life due to variant pressures. \n\nDid god stop at Earth-- well, that is a question which is a matter of belief- if we consider god as a positive force which stimulates life- then no, god wouldn't have stopped only on Earth. \n\nSome research even claims that there are other solar systems with other stars (like our Sun) in which a planet is very like Earth- almost same which supports life. \n\nSo, whether life is or not- is a personal decision. I think there is- but as you say, there is no real solid evidence supporting or contradicting existence of life in other planets
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Cells are made from atoms--life is carbon based.  God is amazing, yes?  I don't see how any of this could have happened by accident!\n\nRemember, the only way to Paradise is through accepting Jesus as Savior!
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Keywords:\n              Help\n\nCarbon has a unique place in our lives. Each living cell, food, wood, paper, petro-chemicals, cooking gas, perfumes, etc are all made up of carbon. Chemistry of carbon compounds is known as organic chemistry. Organic chemistry encompasses study of all carbon-hydrogen compounds. These are also called hydrocarbons. Inorganic carbon chemistry is the study of oxides, nitrides and allotropes of carbon.\n\nThere are many differences between organic and inorganic compounds. Organic compounds are mostly insoluble in water. They have low melting points and exist by forming covalent bonds. Inorganic compounds on the other hand usually dissolve in water and have high melting points. Inorganic compounds can be formed due to either ionic or covalent bonds. Another characteristic of organic compounds is that they are inflammable.\n\nCarbon has 6 protons, 6 neutrons and 6 electrons. Its chemical symbol is 12C 6. Its electronic configuration is 2 electrons in the K-shell, and 4 electrons in the L-shell. In principle it should either give up or borrow 4 electrons while forming compounds. But it doesn’t form ionic bonds at all. It likes to share its four electrons with other atoms and form covalent bonds instead. Carbon covalent bonds are the strongest in nature.\nWe might expect that a carbon atom to form three bonds of one kind using the p orbital electrons and one bond of another kind using the s orbital electron. But this does not happen!! The one 2s and three 2p orbitals mix together and give rise to four new altogether different types of orbitals. This is called  hybridization and is seen only in carbon atom. The four orbitals are at an angle of 109028’. This is called tetrahedral or sp3 (pronounced as sp three) type of hybridization. There are sp2 and sp types of hybridization also.
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carbon and oxygen are in the same group in the periodic table, this means that they have the same amount of electrons in their outer shells. it is these electrons that are involved in every chemical reaction. so, because oxygen and sulfur are elements that are similar in size and have the same amount of electrons in their outer shells, they react similarly.