Module 7

1. Module 7 Part II The Carbon Cycle

2. Chapter 8 Carbon on Earth

3. The Chemistry of Carbon • Biotic carbon • Highly organized molecules within living things • Abiotic carbon • After life they become disorganized goo – called kerogen, or humic acids

4. Terrestrial PlanetsVenus, Earth, and Mars All three planets had about the same amount of carbon: Venus has the carbon content in it’s very dense atmosphere of carbon dioxide and sulfuric acid Earth has the highest concentration of carbon in limestone and rocks Mars has it’s carbon locked up in the polar ice caps that are carbon dioxide dry ice

5. Organic Carbon The backbone of life A means of storing energy Photosynthesis, carbon dioxide, water, and sunlight produces plants that store energy as food The early plants were converted to fossil fuels – more stored energy as fuel instead of food

6. Oxidation states, electron bookkeeping Methane is totally reduced carbon, has an oxidation state of -4 To calculate oxidation states we assign the common states to hydrogen and oxygen, then realize that the molecule has to be neutral, so the leftover number is assigned to carbon Hydrogen is +1, there are four of them in methane, so the carbon must be -4 This is fully reduced carbon Reduced carbon is easily oxidized CH4 + 2 O2→ CO2 + 2 H2O

7. Oxidized carbon CO2 is fully oxidized The oxidation number for carbon is +4 We calculate this by assigning -2 to each oxygen (Group 16 in the periodic table, needs two more electrons) Oxygen is -4, so carbon must be +4 Oxidized carbon is stable, low energy, and the preferred state for carbon Oxidized carbon will not become reduced carbon without a great deal of effort In between is the carbohydrates, where carbon has a zero oxidation state CH2O formaldehyde, is the simplest carbohydrate. O is -2, H is +1(x2) so C must be in the 0 oxidation state

8. Carbon forms Photosynthesis uses oxidized carbon to reduce the carbon to carbohydrates We use carbohydrates as fuel and oxidize the carbohydrate back to CO2 when we exhale during respiration Animals are not the only organisms to breathe!

9. The Land Breathes

10. The land inhales CO2 in the summertime growing season and exhales during the winter months Reversed in the Southern Hemisphere where there is less land The land breathes on an annual cycle

11. The Ocean Breathes

12. The carbon is inorganic, and stable, it involves the carbonate buffer system that we will study in chapter 10, this is called dissolved inorganic carbon The ocean effects atmospheric CO2 on time scales of centuries The glacial-interglacial cycles were amplified somehow by the ocean carbon cycle.

13. The Rocks Breathe

14. The sedimentary rock carbon pool is larger than the ocean, land or atmospheric pools Carbon in the solid Earth exists as limestone CaCO3, and to a lesser extent, organic carbon Most of the organic carbon in sedimentary rocks is kerogen Kerogen is useless as a fossil fuel because it is too diluted The solid Earth is the largest but slowest breathing of the carbon reservoirs

15. The Atmosphere is the Grand Central Station for the CO2 Cycles

16. Glacial-Interglacial Cycles The beat of the ice-age rhythm apparently originates from variation in the Earth’s orbit around the sun The orbit varies through three main cycles, and the orbital variations drive climate by changing the distribution of sunlight at the Earth’s surface 1. Precession Cycle 2. Obliquity Cycle 3. Eccentricity Cycle

17. Precession The axis of rotation spins like a wobbly top Called the precession of season, or the precession of the equinoxes Completes the entire circle in 20,000 years Solar heat influx variability comes from precession Seasonal cycle in the North is weakened and in the South it is intensified because the Earth is closest to the sun in the winter season in the northern hemisphere

18. Precession orbital cycle

19. Obliquity The angle of the pole of rotation relative to the plane of Earth’s orbit Varies between 22 and 25.5 degrees Angle of tilt is currently 23.5 degrees Cycle time is 41,000 years The impact of obliquity on solar heating is strongest in the high latitudes

20. Obliquity of Earth’s Orbit

21. Eccentricity The third cycle involves how elliptical the orbit of the Earth is The eccentricity of the orbit has cycles of 100,000 and 400,000 years At present the orbit of Earth is nearly circular The orbital cycles affect climate by redistributing the energy from one place to another and from one season to another

22. Milankovitch cycles

23. The CO2 Thermostat At the cool surface of the Earth, oxidized carbon wants to be calcium carbonate – limestone In the hot interior of the Earth, oxidized carbon wants to be free, as CO2 The CO2 thermostat regulates atmospheric CO2 and climate on geologic time scales of hundreds of thousands of years It is possible to change the set point of the thermostat, creating a hot house world like that of the dinosaurs, or an icy world like today The thermostats of Venus and Mars are broken

24. Take home points of chapter 8 1. the most stable form of carbon on Earth is oxidized. Photosynthesis stores energy from the sun by producing organic carbon, which is the backbone of life 2. There is less carbon in the atmosphere that any other carbon reservoir. These other reservoirs tug on atmospheric CO2 seasonally for the land, and on glacial interglacial 100,000 year time scales from the ocean 3. The weathering of igneous rocks on land controls the partial pressure of CO2 in the atmosphere on million year time scales. The thermostat is broken on Venus because no water, and on Mars because there is no volcanic activity left.

25. Chapter 9 Fossil Fuels and Energy

26. Energy All energy comes from the stars, Mostly from our sun Previous definition: watts = joules/second terawatts = 1012 watts, written TW 1,000,000,000,000 watts

27. Energy sources Wind (Denmark) Hydroelectric (2% globally) Solar Biomass energy

28. Energy sources Non-renewable Fossil fuels Radioactive elements Renewable • Geothermal • Solar • Wind • Wood • Waste electric power

29. Fossil Fuels “Only a small fraction of the buried organic carbon is in a convenient form for fuel”

30. Traditional fossil fuels Largest reservoir is coal: it was produced in swamps where the organic material was protected from the atmosphere by water Freshwater has less sulfur, burns “cleaner” Saltwater swamps contains sulfur, burns to forms aerosols and produce acid rain as sulfuric acid

31. Coal • Begins as plant material (carbon based) Carbon Peat Coal By a pressure and temperature process that takes millions of years. The oldest coal is the cleanest coal.

32. “Coal is the most abundant fossil fuel, and the future of the Earth’s climate depends mostly on what happens to that coal”

33. Coal in power plants Coal fired power plants are established They produce cheap energy Would be very expensive to replace with a cleaner fuel source until the necessity arises

34. “Oil is probably the most convenient but the least abundant of the fossil fuels, so it is the most expensive.”

35. Source of oil Organic rich sediments buried 2-5 km 50 – 150 ° C Temperature and pressure converts some of the organics to oil Higher temperatures produce natural gas, mostly methane Only a tiny fraction of the oil and gas produced can be harvested

36. Oil is the most expensive • Oil fuels the transportation industry • More energy per weight than any battery (so far) • Convenient liquid form as opposed to: • Coal, not used in transportation since the steam engine • Natural gas which must be a pressurized container

37. Sources Traditional: Oil fields – pumped from under ground or water largest fields in Saudi Arabia, and in Kuwait Non-traditional: Oil shales – low grade fuel for power plants, Estonia produces about 70% Tar sands – requires steam (Canada)

38. How long will it last? We have differing opinions here: The oil industry has been saying forty years for a long time but new sources and initiatives keep adding time. “There is enough oil to keep pumping for decades, but the peak rate of oil extraction could be happening right now.”

39. Natural gas Coal – solid Oil – liquid Natural gas – gas usually in the form of methane CH4

40. Energy of methane “Methane carries more energy per carbon that the others because methane is the most chemically reduced form of carbon.” Reduced form + oxygen → oxidized form + water Along with a release of energy (the ability to do work).

41. Global sources of Energy in 2001

42. Biggest users of energy Energy consumption per dollar GPD (Gross Domestic Productivity). China India Brazil U.S. France Denmark Japan

43. Energy Consumption per person U.S. Japan France Denmark Brazil China India

44. Source? U.S. petroleum, gas, coal Japan petroleum, gas, coal France petroleum, gas, coal Denmark petroleum, gas, coal Brazil petroleum, gas, coal China coal, petroleum, gas India coal, petroleum, gas

45. New coal plants • http://ingienous.com/?page_id=8399 China and India are building new coal fired plants at an alarming rate.

46. Bottom Line “Coal is the form of fossil fuel with the potential of increasing the temperature past the turning point of 2° C. The future of the earth depends most on what happens to that coal.”

47. Take home points, Chapter 9 Ultimately, the energy available to humankind includes instantaneous solar energy, which is abundant but spread out; stored solar energy is in the form of fossil fuels; and stored solar energy from stellar explosions in the form of radioactive elements. Of the fossil fuels, coal is the most abundant. Oil may run out in the coming decades, and the peak rate of oil extraction may be upon us even now.

48. continued…. We can project energy demand in the future as the product of population, economic growth, and energy efficiency.

49. Chapter 10 The Perturbed Carbon Cycle The atmosphere ain’t what it used to be!

50. Ozone Three oxygen atoms Very reactive O2 bonds break with UV-c, forming O free radical, recombines with an O2 to form O3 Stratospheric O3 absorbs (filters) UV-b radiation, forming O2