THE EARTHS LIFE SUPPORT SYSTEMS The biosphere consists of several physical layers that contain: Air Air Water Water Soil Soil Minerals Minerals Life Life Figure 3-6 Fig. 3-6, p. 54 Lithosphere (crust, top of upper mantle) Rock Soil Vegetation and animals Atmosphere Oceanic Crust Continental Crust Lithosphere Upper mantle Asthenosphere Lower mantle Mantle Core Biosphere Crust Crust (soil and rock) Biosphere (living and dead organisms) Hydrosphere (water) Atmosphere (air) Biosphere Atmosphere Membrane of air around the planet. Membrane of air around the planet. Hydrosphere All the earths water: liquid, ice, water vapor All the earths water: liquid, ice, water vapor Lithosphere The earths crust and upper mantle. The earths crust and upper mantle. Earths Spherical Layers 1. Atmosphere A thin envelope of air around the planet. Consists of the: Troposphere = inner layer of the atmosphereTroposphere = inner layer of the atmosphere Where we live & where the atmosphere is thickest Has variable amounts of water vapor (1-4%) [most abundant nonanthropogenic GHG] = this layer experiences weather Extends 17 km (11 mi) above sea level Contains most of the planets air (78% N 2, 21% O 2, 1% argon, & 0.039% CO 2 ) - & other trace greenhouse gases Ground-level ozone (O 3 ) & smog (from NO x ) Earths Spherical Layers 1. Atmosphere Stratosphere =Stratosphere = Stretches km (11-30 mi) above earths surface Its lower portion contains ozone (O 3 ) to filter out most of the suns harmful UV radiation (UVA, UVB, & UVC) Mesosphere =Mesosphere = Characterized by temperatures that quickly decrease as height increases Characterized by temperatures that quickly decrease as height increases Here, meteors coming too close to earth burn up Here, meteors coming too close to earth burn up Earths Spherical Layers 1. Atmosphere Thermosphere = largest of all the layersThermosphere = largest of all the layers Typically about 200C (360F) hotter in the daytime than at night (temps here could be 500C to 2,000F!) The air density here is so low that most of the thermosphere is what we normally think of as outer space Exosphere = outermost layer of the atmosphereExosphere = outermost layer of the atmosphere Temps & pressures are the lowest Coldest part of the lower atmosphere. Thermal boundary. Ozone layer Layer where meteorites burn up. Coldest recorded temperature of - 80C!!! Virtually no air temperatures can be very high due to solar radiation. Atmosphere Structure What Sustains Life on Earth? Solar energy, the cycling of matter, and gravity sustain the earths life. Figure 3-7 Fig. 3-7, p. 55 Nitrogen cycle Biosphere Heat in the environment Heat Phosphorus cycle Carbon cycle Oxygen cycle Water cycle What Sustains Life on Earth? Three interconnected factors: Three interconnected factors: 1. The one-way flow of high-quality energy from the sun Through materials & living things in their feeding interactions Into the environment as low-quality energy (mostly as heat dispersed into air or water molecules at a low temp) Eventually back into space as heat What Happens to Solar Energy Reaching the Earth? Solar energy flowing through the biosphere warms the atmosphere, evaporates and recycles water, generates winds and supports plant growth. Figure 3-8 Fig. 3-8, p. 55 Absorbed by ozone Visible Light Absorbed by the earth Greenhouse effect UV radiation Solar radiation Energy in = Energy out Reflected by atmosphere (34% ) Radiated by atmosphere as heat (66%) Heat radiated by the earth Heat Troposphere Lower Stratosphere (ozone layer) What Sustains Life on Earth? 2. The cycling of matter through parts of the biosphere Matter: the atoms, ions, or molecules needed for survival by living things The earth is closed to inputs of matter from space. Therefore, all the nutrients used by organisms are already present on earth and must be recycled for life to continue What Sustains Life on Earth? 3. Gravity Allows the planet to hold on to its atmosphere Allows the planet to hold on to its atmosphere Causes the downward movement of chemicals in the matter cycles Causes the downward movement of chemicals in the matter cycles MATTER CYCLING IN ECOSYSTEMS Nutrient Cycles: Global Recycling Global Cycles recycle nutrients through the earths air, land, water, and living organisms. Global Cycles recycle nutrients through the earths air, land, water, and living organisms. Nutrients are the elements and compounds that organisms need to live, grow, and reproduce. Nutrients are the elements and compounds that organisms need to live, grow, and reproduce. Biogeochemical cycles move these substances through air, water, soil, rock and living organisms. Biogeochemical cycles move these substances through air, water, soil, rock and living organisms. The Water Cycle Figure 3-26 Fig. 3-26, p. 72 Precipitation Transpiration Condensation Evaporation Ocean storage Transpiration from plants Precipitation to land Groundwater movement (slow) Evaporation from land Evaporation from ocean Precipitation to ocean Infiltration and Percolation Rain clouds Runoff Surface runoff (rapid) Water Unique Properties There are strong forces of attraction between molecules of water. Water exists as a liquid over a wide temperature range. Liquid water changes temperature slowly. It takes a large amount of energy for water to evaporate. Liquid water can dissolve a variety of compounds. Water expands when it freezes. How is Water Cycled in the Biosphere? The hydrologic cycle collects, purifies, & distributes the earths fixed supply of water The hydrologic cycle collects, purifies, & distributes the earths fixed supply of water Main processes involved: Main processes involved: 1. Evaporation : liquid to gas 2. Transpiration : movement of water upward from soil to roots out through the leaves of plants 3. Condensation : gas to liquid 4. Precipitation : rain, sleet, hail, snow 5. Infiltration : movement of water into soil 6. Percolation : downward flow of water through soil & permeable rocks to groundwater storage areas = aquifers 7. Runoff : downslope surface movement back to the sea to resume the cycle The Water Cycle Powered by energy from the sun and by gravity Incoming solar energy evaporates water from oceans, streams, lakes, soil, & vegetation The oceans hold 97% of all water on the planet and are the source of 78% of all global precipitation About 86% of water vapor in the atmosphere comes from oceans, the rest from land The Water Cycle The amount of water vapor air can hold depends on its temperature, with warm air holding more water vapor than cold air Absolute humidity = the amount of water vapor found in a certain mass of air & is usually expressed as grams of water per kg of air Absolute humidity = the amount of water vapor found in a certain mass of air & is usually expressed as grams of water per kg of air Relative humidity = the amount of water vapor in a certain mass of air, expressed as a percentage of the maximum amount it could hold at that temp Relative humidity = the amount of water vapor in a certain mass of air, expressed as a percentage of the maximum amount it could hold at that temp Ex: Relative humidity of 60% at 27C (80F) = each kg of air contains 60% of the maximum amount of water vapor it could hold at that tempEx: Relative humidity of 60% at 27C (80F) = each kg of air contains 60% of the maximum amount of water vapor it could hold at that temp The Water Cycle Winds and air masses carry water vapor over various parts of the earths surface, often over large distances Winds and air masses carry water vapor over various parts of the earths surface, often over large distances Falling temperatures cause the water vapor to condense into tiny droplets that form clouds or fog Falling temperatures cause the water vapor to condense into tiny droplets that form clouds or fog The temperature at which condensation occurs = dew point The temperature at which condensation occurs = dew point For precipitation to occur, air must contain condensation nuclei (tiny particles on which droplets of water vapor can collect) For precipitation to occur, air must contain condensation nuclei (tiny particles on which droplets of water vapor can collect) Sources of such particles: volcanic ash, soil dust, smoke, sea salts, particulate matter emitted by factories, etc) The Water Cycle Most of the precipitation falling on terrestrial ecosystems becomes surface runoff flowing into streams & lakes, which eventually carry water back into the oceans where it can be evaporated into the cycle again Most of the precipitation falling on terrestrial ecosystems becomes surface runoff flowing into streams & lakes, which eventually carry water back into the oceans where it can be evaporated into the cycle again Surface runoff can also cause soil erosion, which moves soil & weathered rock fragments from one place to another Water dissolves many nutrient compounds, therefore it is a major medium for transporting nutrients within & between ecosystems Effects of Human Activities on Water Cycle We alter the water cycle by: Withdrawing large amounts of freshwater. Withdrawing large amounts of freshwater. Clearing vegetation and eroding soils. Clearing vegetation and eroding soils. Polluting surface and underground water. Polluting surface and underground water. Contributing to climate change. Contributing to climate change. The Carbon Cycle: Part of Natures Thermostat Figure 3-27 How is Carbon Cycled in the Biosphere? Carbon is essential to life it is the basic building block of carbohydrates, fats, proteins, & DNA The carbon cycle is based on carbon dioxide gas, which makes up 0.036% of the volume of the troposphere & is also dissolved in water CO 2 is a key component of natures thermostat Not enough CO 2 in the atmosphere = too cold Not enough CO 2 in the atmosphere = too cold Too much CO 2 in the atmosphere = too hot Too much CO 2 in the atmosphere = too hot The Carbon Cycle Photosynthesis & Aerobic Respiration are 2 main processes involved 1. Terrestrial producers remove CO 2 from the atmosphere & aquatic producers remove it from the water (for photosynthesis) 2. The cells in oxygen-consuming producers, consumers, & decomposers carry out respiration to break down glucose & convert the carbon back to CO 2 in the atmosphere/water for reuse by producers The Carbon Cycle Over millions of years, buried deposits of dead plant matter & bacteria are compressed between layers of sediment, where they form carbon-containing fossil fuels, such as coal and oil. Over millions of years, buried deposits of dead plant matter & bacteria are compressed between layers of sediment, where they form carbon-containing fossil fuels, such as coal and oil. The carbon is not released into the atmosphere as CO 2 for recycling until: The carbon is not released into the atmosphere as CO 2 for recycling until: 1. These fuels are extracted & burned 2. Long-term geological processes expose these deposits to air In only 100 years, we have extracted & burned fossil fuels that took millions of years to form In only 100 years, we have extracted & burned fossil fuels that took millions of years to form The Carbon Cycle Oceans & forests are major carbon-storage reservoirs (carbon sinks) Oceans & forests are major carbon-storage reservoirs (carbon sinks) Oceans also play a major role in regulating the CO 2 level: Oceans also play a major role in regulating the CO 2 level: 1. CO 2 stays dissolved in the sea 2. Some is removed by photosynthesizing producers 3. Some reacts with seawater to form carbonate ions (CO 3 2- ) and bicarbonate ions (HCO 3 - ) As water warms, more dissolved CO 2 returns to the atmosphere (just as more CO 2 fizzes out of a soda when it warms) As water warms, more dissolved CO 2 returns to the atmosphere (just as more CO 2 fizzes out of a soda when it warms) The Carbon Cycle In marine ecosystems, some organisms (coral) take up dissolved CO 2 molecules, carbonate ions, or bicarbonate ions from ocean water (this makes ocean water more basic) In marine ecosystems, some organisms (coral) take up dissolved CO 2 molecules, carbonate ions, or bicarbonate ions from ocean water (this makes ocean water more basic) These ions can then react with Calcium (Ca 2+ ) in seawater to form slightly soluble carbonate compounds (calcium carbonate: CaCO 3 )to build shells & skeletons of marine organisms These ions can then react with Calcium (Ca 2+ ) in seawater to form slightly soluble carbonate compounds (calcium carbonate: CaCO 3 )to build shells & skeletons of marine organisms The more acidic the water, the more soluble the CaCO 3 instead, it dissolves in the ocean water making it more acidic (+ feedback) As these organisms die, their shells & bones sink to ocean depths where they stay buried for eons under immense pressure eventually forming limestone rock As these organisms die, their shells & bones sink to ocean depths where they stay buried for eons under immense pressure eventually forming limestone rock Limestone is the largest carbon reservoir in the cycle The Carbon Cycle Major Reservoirs or Sinks of Carbon Plant Matter: Photosynthesis Plant Matter: Photosynthesis Terrestrial Biosphere: Forests store most of the above-ground and soil carbon Terrestrial Biosphere: Forests store most of the above-ground and soil carbon Oceans: dissolved CO 2 & living/nonliving biota (shells & skeletons) Oceans: dissolved CO 2 & living/nonliving biota (shells & skeletons) Sedimentary deposits: limestone & carbon trapped in fossil fuels Sedimentary deposits: limestone & carbon trapped in fossil fuels Carbon is Released Back into the Atmosphere Through: Cellular respiration: Aerobic releases CO 2 & anaerobic releases CH 4 Cellular respiration: Aerobic releases CO 2 & anaerobic releases CH 4 Decay by decomposers: same results as above (livestock: CH 4 ) Decay by decomposers: same results as above (livestock: CH 4 ) Burning fossil fuels, wood, coal Burning fossil fuels, wood, coal Slash & burn (clear-cutting) forests: oxidation of C Slash & burn (clear-cutting) forests: oxidation of C Weatherization of rocks: (i.e., limestone, marble, & chalk) which break down into CO 2 and H 2 CO 3 Weatherization of rocks: (i.e., limestone, marble, & chalk) which break down into CO 2 and H 2 CO 3 Volcanic eruptions Volcanic eruptions Release of CO 2 by warmer oceans Release of CO 2 by warmer oceans How are Human Activities Affecting the Carbon Cycle? Especially since 1950, humans have: Especially since 1950, humans have: 1. Cleared trees & other plants that absorb CO 2 2. Added large amounts of CO 2 by burning fossil fuels This additional atmospheric CO 2 is adding to the natural greenhouse effect that helps warm the troposphere & the earths surface This additional atmospheric CO 2 is adding to the natural greenhouse effect that helps warm the troposphere & the earths surface The result is global warming which could: The result is global warming which could: 1. Disrupt global food production 2. Raise the average sea level in various parts of the world 3. Actually make ozone depletion worse Fig. 3-28, p. 74 CO 2 emissions from fossil fuels (billion metric tons of carbon equivalent) Year Low projection High projection The Nitrogen Cycle: Bacteria in Action Figure 3-29 Fig. 3-29, p. 75 Gaseous nitrogen (N 2 ) in atmosphere Ammonia, ammonium in soil Nitrogen-rich wastes, remains in soil Nitrate in soil Loss by leaching Loss by leaching Nitrite in soil Nitrification Ammonification Uptake by autotrophs Excretion, death, decomposition Loss by denitrification Food webs on land Fertilizers Nitrogen fixation How is Nitrogen Cycled in the Biosphere? The abundant N 2 in the atmosphere cannot be absorbed & metabolized directly as a nutrient by plants/animals The abundant N 2 in the atmosphere cannot be absorbed & metabolized directly as a nutrient by plants/animals Two ways N 2 gets converted into compounds that can enter food webs: Two ways N 2 gets converted into compounds that can enter food webs: 1. Lightning causes N and O in the atmosphere to react & produce oxides of nitrogen: N 2 + O 2 2NO 2. Specialized processes performed by certain bacteria in the soil & aquatic systems The Nitrogen Cycle 1. Nitrogen Fixation: in addition to lightning, specialized bacteria convert N 2 to ammonia (NH 3 ): N 2 + 3H 2 2NH 3 Cyanobacteria (blue-green algae) in soil & water Rhizobium bacteria in small nodules on the root systems of many plants (legumes: soybeans & alfalfa) 2. Nitrification: Two-step process by specialized aerobic bacteria that converts ammonia in soil to: Nitrite ions (NO 2 - ) = toxic to plants Nitrate ions (NO 3 - ) = easily taken up by plants as a nutrient Nitrous oxide (N 2 O) is also emitted (a significant greenhouse gas) The Nitrogen Cycle 3. Assimilation: plants roots absorb inorganic ammonia, ammonium ions (NH 4 + ), & nitrate ions in soil & water These ions can be used to make DNA, amino acids, & proteins Animals get their nitrogen by eating plants or plant-eating animals 4. Ammonification: Specialized decomposer bacteria/fungi convert nitrogen-rich organic compounds, wastes, & dead organisms into: Simpler nitrogen-containing inorganic compounds (i.e., NH 3 ) Water-soluble salts containing ammonium ions The Nitrogen Cycle 5. Denitrification: Specialized bacteria (mostly anaerobic bacteria in waterlogged soil or in the bottom of sediments of lakes, oceans, swamps, & bogs) convert NH 3 & NH 4 + back into nitrite and nitrate ions & then into N 2 & nitrous oxide gas (N 2 O) This begins the nitrogen cycle again This begins the nitrogen cycle again