Carbon dioxide and methane.
As an element, carbon occurs in a striking variety of forms. Coal, soot, and diamonds are all nearly pure forms of carbon. Carbon also occurs in a form, discovered only recently, known as fullerenes or buckyballs. Buckyball carbon holds the promise for opening a whole new field of chemistry (see accompanying sidebar). Another highly important and very unusual property of carbon is its ability to form long chains. It is not unusual for two atoms of an element to combine with each other. Oxygen (O 2), nitrogen (N 2), hydrogen (H 2), chlorine (Cl 2), and bromine (Br 2) are a few of the elements that can do this. Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is present in all forms of carbon-based life, and in the human body carbon is the second most abundant element by mass (about 18.5%) after oxygen. Carbon (from Latin: carbo coal) is a chemical element with symbol C and atomic number 6. On the Periodic table, it is the first (row 2) of six elements in column (group) 14, which have in common the composition of their outer electron shell. Introduction: Carbon is everywhere! Carbon is the fourth most abundant element in the universe and is the building block of life on Earth. Carbon exists in pure forms such as a diamond or graphite or in the millions of different kinds of carbon compounds scientists have currently identified. We use carbon compounds such as wood to build and heat our homes. Uses of Carbon. Carbon (in the form of coal, which is mainly carbon) is used as a fuel. Graphite is used for pencil tips, high temperature crucibles, dry cells, electrodes and as a lubricant. Diamonds are used in jewelry and – because they are so hard – in industry for cutting, drilling, grinding, and polishing.  Carbon compounds can exist as solids (such as diamonds or coal), liquids (such as crude oil), or gases (such as carbon dioxide). Carbon is often referred to as the building block of life because living things are based on carbon and carbon compounds. The Carbon Cycle. Source: NASA. It takes many forms and moves through the environment via the carbon cycle. The carbon cycle is the circulation and transformation of carbon back and forth between living things and the environment. Carbon is an element, something that cannot be broken down into a simpler substance. Carbon has two  naturally occurring pure forms (allotropes), which are graphite and  diamond.  Graphite is a silver  grey powder which consists of planes of carbon atoms a … rranged in  interlocking hexagons. There are two kinds of bonds within the  sheets, covalent and delocalised. Charcoal-a form of non-crystalline carbon   Graphite-crystalline carbon-known as 'pencil llead' (although there is no lead in it!). In graphit, the atoms are joined t … ogether in flat sheets.   Diamond-crystalline carbon with the carbon atoms arranged differently from graphite-in a huge 3d matrix. Carbon is also a major component of many minerals. Carbon also exists in various forms in the atmosphere. Carbon dioxide (CO 2) is partly responsible for the greenhouse effect and is the most important human-contributed greenhouse gas. In the past two centuries, human activities have seriously altered the global carbon cycle, most significantly in the atmosphere Carbon in the earth's atmosphere exists in two main forms: carbon dioxide and methane. Both of these gases absorb and retain heat in the atmosphere and are partially responsible for the greenhouse effect.  Carbon in the earth's atmosphere exists in two main forms: carbon dioxide and methane. Both of these gases absorb and retain heat in the atmosphere and are partially responsible for the greenhouse effect. Carbon also exists in various forms in the atmosphere. Carbon dioxide (CO 2) is partly responsible for the greenhouse effect and is the most important human-contributed greenhouse gas.
http://www.chemistryexplained.com/elements/A-C/Carbon.html https://en.wikipedia.org/wiki/Carbon http://serc.carleton.edu/eslabs/carbon/lab1.html http://www.chemicool.com/elements/carbon.html http://teeic.indianaffairs.gov/er/carbon/carboninfo/cycle/ http://www.answers.com/Q/Why_can_pure_element_of_carbon_exist_in_different_forms https://en.wikipedia.org/wiki/Carbon_cycle http://www.weegy.com/?ConversationId=D5E5CF8B https://en.wikipedia.org/wiki/Carbon_cycle
what forms does carbon exist in