The Carbon Story • The stuff of life • All you ever wanted to know but were afraid to ask.
Atoms and molecules • The simplest known substances are called “elements” • an element has only one type of atom • There are 92 naturally occurring elements • all other substances are made up from assemblages of elements
Protons, electrons, neutrons • an element is defined by its atomic structure • all atoms of a given element have the same number of protons and electrons • this number determines its chemistry • some atoms of an element may have a different number of neutrons • they are chemically the same but of slightly different mass
Isotopes of Carbon • all carbon atoms have six electrons and six protons • most carbon atoms also have 6 neutrons • some carbon atoms have 7 or 8 neutrons. • carbon 14 (6p + 8n) is radioactive and has a half life of 5,730 years and decays into nitrogen • it is constantly being created as cosmic rays strike nitrogen atoms in the atmosphere • the amount of carbon 14 in the atmosphere is reasonably constant. (1 part per trillion)
Carbon dating • the carbon dioxide taken up by plants therefore contains a known proportion of carbon 14 • when the plant dies, the carbon 14 level slowly decays as carbon 14 breaks down back into nitrogen • the amount of carbon 14 in a sample compared to its carbon 12 is an indicator of its age. • carbon dating is useful for periods of time measured in thousands of years • dating the carbon in charcoal from ancient fires tells us that aboriginal people have lived in Australia for something like 40,000 years
Allotropes • some elements present in more than one physical form • the two forms usually have the same chemistry • in the case of carbon the two forms are: • graphite (one of the softest substances known) • diamond (the hardest naturally occurring substance)
carbon atoms are able to bond to each other • they do this by sharing pairs of electrons • this gives carbon some interesting and unique properties • for example, carbon atoms can combine into long chains or into rings
Diamond • under the right circumstances of temperature and pressure, carbon atoms can link up into a grid • each atom has 4 neighbours arranged at the points of a tetrahedron • this is a very strong and rigid structure • but…
although diamond is very hard and can scratch steel and glass • it is very fragile and will shatter if stuck • because it is pure carbon it will burn to form carbon dioxide. • because there are no free electrons diamond is an insulator.
Graphite • the carbon atoms are arranged into a planar hexagonal grid • these layers of grids are not linked and can slide over each other • graphite is very soft • each atom is linked to three other atoms • there are free electrons which can move - graphite is a good conductor of electricity
graphite has many familiar forms • pencil “lead” is actually graphite mixed with clay • charcoal (partly burnt wood) • activated charcoal, formed by heating charcoal in steam, is a useful filter substrate • lampblack formed as ‘soot’ when oils burns in a limited air supply • boneblack derived from animal bones • coal • coke
Carbonates and bicarbonates • the radicals CO3 & HCO3 are commonly occurring and found in most homes • washing soda - Na2CO3 • bi-carb soda - NaHCO3 • limestone and marble CaCO3
carbonate and bi-carbonate radicals are formed when carbon dioxide dissolves in water • CO2 + H2O ----> H2CO3 ----> 2H+ + CO32- • hydrogen ions are the basic part of acids • this makes the water mildly acidic • under pressure, more carbon dioxide will dissolve in water • when the pressure is released the gas comes back - ‘aerated’ or carbonated waters and sparkling wines, ‘soda siphon’
some carbonates are water soluble • some carbonates are not water soluble • the test for CO2 is to pass the gas into ‘lime water’ • Ca(OH)2 + CO2 ----> CaCO3 + H2O • the calcium carbonate is insoluble and makes the water go cloudy. • adding further CO2 clears the water again • CaCO3 + H2O + CO2 ----> Ca(HCO3)2 • calcium bicarbonate is water soluble
all rain and ground water contains some dissolved carbon dioxide • such water passing over limestone (CaCO3) will cause it to dissolve • as the water evaporates the carbon dioxide is released and the calcium carbonate re-forms • this is what creates stalactites and stalagmites in limestone caves
carbon dioxide is produced when… • carbonates are heated • acid is added to carbonates or bi-carbonates • carbon is burned in air (or oxygen) • compounds containing carbon are burned in air (or oxygen)
frozen carbon dioxide is called ‘dry ice’ • its freezing temperature is about -80°C • under normal atmospheric pressure it converts from the solid form directly into the gas without going through the liquid phase • liquid carbon dioxide only exists under high pressure • because carbon dioxide is a product of combustion, it cannot burn. It is used in fire extinguishers
carbon monoxide • when carbon or carbon containing substances burn in insufficient oxygen the gas produced is carbon monoxide • carbon monoxide will quickly change to carbon dioxide if exposed to air • it burns with a blue flame • in the human body, carbon monoxide easily combines with haemoglobin in the same way as oxygen but cannot be released • carbon monoxide has no odour
Organic Chemistry • The chemistry of organisms • the chemistry of carbon • the chemistry of life
hydro-carbons • carbon can form into chains of varying lengths • each carbon atom can bond to hydrogen • methane (odourless) found in marsh gas CH4 • ethane C2H6 • propane C3H8 • butane C4H10, pentane C5H12, hexane C6H14, heptane C7H16, octane C8H18, nonane C9H20, decane C10H22
Triple bond unsaturated chains Also known as acetylene limestone (calcium carbonate CaCO3) heated to drive off the carbon dioxide to produce quick lime (calcium oxide CaO) calcium oxide heated with coal (carbon C) at about 2000°C in an electric arc furnace (graphite electrodes) CaO + 3 C -----> CaC2 + CO CaC2 + 2 H2O -----> C2H2 + Ca(OH)2
Alcohols also known as wood alcohol - poisonous, leading to blindness and death. this is the alcohol in wines, beers, spirits etc. It is a mild anaesthetic and depressant. Denatured alcohol, also known as methylated spirits is ~90% ethanol and ~10% methanol with a small amount of pyridine (nasty smell) There is a whole series of alcohols, systematically named: propanol, butanol, pentanol etc.
trinitrotoluene black = carbon white = hydrogen blue = nitrogen red = oxygen vanillin Aromatics & other interesting compounds 6 carbon atoms can link up in a hexagonal ring. On close examination you can see that each carbon has only three bonds. The ring indicates that there are 6 unbonded electrons which appear to exist distributed around the ring rather than belonging to a particular atom. Hydrogens can be replaced by other atoms or radicals. An OH (hydroxyl group) makes an alcohol. Here a methyl radical creates toluene. Vanilla essence! Let’s get rid of those silver fish!
Acetone Citral Other stuff The ether used as an anaesthetic is di-ethyl ether C2H5OC2H5 There is a series of aldehydes. This is the one used to preserve tissue specimens There is a whole series of keytones. Acetone is a solvent used in nail polish remover. Citral is present in the oils of several plants, including lemon myrtle (90-98%), Litsea citrata (90%), Litsea cubeba (70-85%), lemongrass (65-85%), lemon tea-tree (70-80%), Ocimum gratissimum (66.5%), Lindera citriodora (about 65%), Calypranthes parriculata (about 62%), petitgrain(36%), lemon verbena (30-35%), lemon ironbark (26%), lemon balm (11%), lime (6-9%), lemon (2-5%), and orange.
Acetic acid vinegar Citric acid Organic Acids Organic acids are characterised by a COOH group attached to a chain. Formic acid is the characteristic smell and bite of ants When wines “go off” they become acidic - acetic acid Citric acid is found in lemons. Annual world production (2007) 1.6 M tonnes alcohol + organic acid ----> ester + water
Fatty Acids palmitic acid makes up about 24% of human fat - CH3(CH2)14COOH it is a saturated fat - ie. all single bonds, maximum amount of hydrogen oleic acid makes up about 47% of human fat - CH3(CH2)7CH=CH(CH2)7COOH it is an unsaturated fat - ie. it has a double bond a poly unsaturated fatty acid has multiple double bonds
CH2OOCR | CH2OOCR + 3 NaOH -----> | CH2OOCR fat/oil CH2OH | CHOH + 3 RCOO-Na+ | CHOH glycerol soap glycerol, glycerine Soap Take a triglyceride fat or oil and boil it up in sodium hydroxide (lye) and water Add salt (NaCl) and the soap comes out of the solution. This is why bath soap doesn’t work in salt water. Soap has an organic end (left) and an inorganic, water soluble end. Detergent CH3(CH2)17OSO3-Na+
poly ethylene polythene neoprene poly vinyl chloride pvc vinyl chloride Polymers
Carbohydrates sugars, starches, cellulose The sugar we buy in the supermarket is called sucrose. It is called a disaccharide because it is actually formed from two other simple sugars. It has the nominal formula C6H12O6. Note the ratio of hydrogen to oxygen (H2O) Glucose C6H12O6 H | C=O | HO-C-H | H-C-OH | HO-C-H | HO-C-H | H-C-OH | H Fructose C6H12O6 H | HO-C-H | HO-C=O | H-C-OH | HO-C-H | HO-C-H | H-C-OH | H Starches have many more carbons in their structure. There are alternate models including ring structures Starches can be broken down into simple sugars Some animals can break down cellulose into starches and sugars
The Carbon Cycle Why growing trees is not the answer!
moss cells under the microscope Photosynthesis In the presence of light, the green structures inside plant cells called chloroplasts are the sites where carbon dioxide and water are converted into carbohydrates. Oxygen is released as a waste product. CO2 + H2O --light-> carbohydrate + O2 The green chemical is called chlorophyll. Oxygen is very reactive. Metals quickly corrode in air because of the presence of oxygen. So reactive is it, that it cannot exist in the atomic state so it is found in molecules as atom pairs - O2 A second form of oxygen known as ozone consists of three atoms of oxygen linked together - O3. It is poisonous and has the characteristic smell associated with sparks. It has a half life of about 30 minutes. It breaks down into O2. It forms in the upper atmosphere where ultraviolet light interacts with O2 to form O3. Oxygen makes up about 20.8% of the air All the oxygen in the atmosphere has been produced by green plants over the last 2.5 billion years. Carbon dioxide makes up about 0.039% of air by volume
Respiration Cellular respiration is the process of combining nutrients, predominantly carbohydrates, with oxygen to release energy to power the chemistry of the cells functions. This process applies to both plants and animals. The waste product is CO2. In the case of an animal, the air breathed out contains less oxygen and more carbon dioxide than the air which is breathed in. Expired air still contains oxygen - that’s why the “kiss of life” works. The raised CO2 content in the lungs triggers the breathing reflex.
The carbon system is dynamic carbon is constantly migrating through various forms carbon is entering and leaving the atmosphere all the time. in the biosphere, carbon is the vector which carries energy collected from the sun into biological processes. As the energy is released the carbon returns to the atmosphere to “go ‘round again” but… Not all carbon is created equal. The key is to be found in the length of the cycle
Not all carbon dioxide is “created” equal. What is important is the time scale associated with its production and removal from the atmosphere. Grass grows during the spring and summer and is eaten by various animals - cattle, sheep, ‘roos, … The life of a tree is of the order of 100 years. In that time a forest will come into a state of equilibrium. After that time the amount of carbon in the forest is largely constant. When a tree dies it is consumed by various other plants and animals. The forest ecosystem has the available nutrients constantly being recycled. Break down of carboniferous material releases carbon dioxide into the atmosphere at the same rate that photosynthesis removes it. A - grasses B - trees C - long lived trees D - oil E - coal
The longest lived trees have life expectancy at around 1000 years. Oil deposits were laid down 70+ million years ago. Some as much as 400 Ma Carbon removed from the air by small marine organisms around 100 Ma has remained stored away from the air in geological basins. Coal deposits age from around 300 Ma. Land plant material has been converted into coal after burial and has remained stored underground. A - grasses B - trees C - long lived trees D - oil E - coal
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Ma (million years ago), to the beginning of the Permian Period, about 299.0 ± 0.8 Ma Terrestrial life was well established by the Carboniferous period. Amphibians were the dominant land vertebrates, of which one branch would eventually evolve into reptiles, the first fully terrestrial vertebrates. Arthropods were also very common and many were much larger than those of today. Vast swathes of forest covered the land, which would eventually be laid down and become the coal beds characteristic of the Carboniferous system Atmospheric carbon dioxide was much higher than it is today. Prolific plant life was removing carbon dioxide from the air to build tissue. As these forests died and were buried, what we now see as coal seams were formed. These seams represent carbon which has been removed from the atmosphere and sequestered underground for hundreds of millions of years.
The Eden Project in Cornwall, England, the world’s largest greenhouse The greenhouse effect Light enters by passing through the glass and falls on the soil and plants inside. This raises the temperature at ground level. The air near the ground is warmed and rises to circulate inside the enclosure. Some heat is radiated back as infra-red radiation to which the glass is only partially transparent. Some of this radiation is reflected back. Atmospheric material acts in the same way. Water vapour, CO2 and CH4 are only partially transparent to infra-red light. This can be a temporary effect. In winter, a cloudless night presages a frosty morning. The ground temperature goes below zero as heat energy is radiated out into space. The air near the ground is cooled close to or below zero. See the difference a cloudy night makes to the temperature at the surface.
Greenhouse gas A greenhouse gas (GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone. In the Solar System, the atmospheres of Venus, Mars, and Titan also contain gases that cause greenhouse effects. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth's surface would be on average about 33 °C colder than at present. Since the beginning of the Industrial Revolution the burning of fossil fuels has contributed to the increase in carbon dioxide in the atmosphere from 280 ppm to 397 ppm, despite the uptake of a large portion of the emissions through various natural "sinks" involved in the carbon cycle. Anthropogenic CO2 emissions (i.e., emissions produced by human activities) come from combustion of carbonaceous fuels, principally wood, coal, oil, and natural gas.
Removing CO2 from the atmosphere Photosynthesis converts CO2 to carbohydrates - the CO2 is stored for periods of 1 to 1000 years CO2 is soluble in water Some of this CO2 is removed from the water by shell building animals as CaCO3 As more CO2 is added, the water becomes acidic insoluble CaCO3 may become water soluble Ca(HCO3)2 The ability of shelled organisms made from CaCO3 to acquire needed calcium is reduced or may stop Keeping CO2 out of the atmosphere Sequestration To be effective, the carbon has to stay out of the atmosphere as part of the normal cycles. Burning oil and coal releases carbon which has been stored for millions of years. To complete the cycle it needs to be removed and stored for equivalent millions of years. Can we capture and store the CO2 in some way? Pump it into deep ground water under pressure? Plough it into the soil?
Climate Change On average, the earth’s surface temperature is rising Since the early 1900’s this has amounted to about 0.8°C 2/3 of that rise has happened since 1980 What effects can be measured? Sea surface temperatures are rising The amount of water in the atmosphere is rising The amount of energy in the atmosphere is increased This energy drives the weather We can expect more extreme weather effects Hot liquids expand Sea level will increase by thermal expansion Ice which is now stored on land (Antarctica, Greenland, glaciers) will melt adding more water to the oceans Sea level will rise
Are there other factors which cause climate change? Anything which effects the relationship between arriving energy from the sun and radiation of energy back into space and anything which effects the movement of energy around the earth Sun activity levels Continental drift Ocean currents Positive feedback Jet streams Precession of the poles Magnetic field reversals Large seismic events Volcanic eruptions Meteors and meteorites Variations in the earth’s orbit
The 10 indicators are: Land surface air temperature as measured by weather stations. You know all those skeptic arguments about how the temperature record is biased by the urban heat island effect, badly-sited weather stations, dropped stations, and so on? This is the only indicator which suffers from all those problems. So if you’re arguing with somebody who tries to frame the discussion as being about land surface air temperature, just remind them about the other nine indicators. Sea surface temperature. As with land temperatures, the longest record goes back to 1850 and the last decade is warmest. Air temperature over the oceans. Lower troposphere temperature as measured by satellites for around 50 years. By any of these measures, the 2000s was the warmest decade and each of the last three decades has been much warmer than the previous one. Ocean heat content, for which records go back over half a century. More than 90% of the extra heat from global warming is going into the oceans – contributing to a rise in… Sea level. Tide gauge records go back to 1870, and sea level has risen at an accelerating rate. Specific humidity, which has risen in tandem with temperatures. Glaciers. 2009 was the 19th consecutive year in which there was a net loss of ice from glaciers worldwide. Northern Hemisphere snow cover, which has also decreased in recent decades. Perhaps the most dramatic change of all has been in Arctic sea ice. Satellite measurements are available back to 1979 and reliable shipping records back to 1953. September sea ice extent has shrunk by 35% since 1979.
Global warming is better described as Climate Change Weather Seasons This is the day to day variation in atmospheric conditions. We a measure: temperature air pressure wind speed and direction precipitation - rain, snow etc. cloud amount sun light This is the annual changes in weather patterns caused by the fact that the earth’s axis is inclined to the plane of the orbit around the sun. The sun apparently changes its vertical position in the sky and therefore the angle at which the suns rays strike the earth’s surface at any given place changes during the year. Climate The long term average of the day to day variations of all the measured quantities This average can be struck for every day of the year - the daily average It can be struck for the whole month It can be taken over the whole year.
Climate is also variable accumulated sediments in lakes can show how run-off varies over a long term the width of some tree rings responds to rainfall and others to temperature ice cores taken in Antarctica hold an annualised record of snow accumulation and give an indication of climate observing geological structures gives an indication of climate - eg. ice ages