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Transcript
Chapter 6: The Biogeochemical Cycles Planets near Earth Inner planets formed by gathering together of particle by gravitational force Would expect Earth, Mars, Mercury and Venus to have a similar atmosphere - they do not Planets Near Earth Earth’s unique atmosphere indicates that it contains life Earth has “environmental fitness” Life evolved in an environment conducive for that to occur Life altered the environment at a global level Rise of Oxygen Before 2.3 billion years ago, the atmosphere was low in oxygen Evidence - grains of pyrite in sedimentary rock (banded iron formations in figure on right) Oceans were filled with dissolved (unoxidized) iron Rise of Oxygen Early photosynthesizers included stromatolites (3.4 billion years old) Early organisms on earth Prokaryotes Simple cell structure Get energy from fermentation Low energy yield to organism Waste products of carbon dioxide and alcohol Live singly or on end-toend chains Cannot form 3-D structures Lacked organelles and a nucleus (too much energy to maintain) Evolution of Biosphere After presence of eukaryotes and oxygenated atmosphere Biosphere started to change drastically Plants, Animals and Fungi Evolved 700–500 million years ago They, in turn, continued to alter the biogeochemical cycles on earth Life and Global Chemical Cycles Micronutrients Elements required in small amounts by all life or moderate amounts by some forms of life Macronutrients 24 elements required by all organisms Include the “Big Six”, which are the building blocks of life Carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur Each plays a special role in organisms Biogeochemical Cycles A biogeochemical cycle is the complete path a chemical takes through the four major components of Earth’s system Atmosphere Hydrosphere Lithosphere Biosphere The Geologic Cycle Rocks and Soil Continually created, maintained, changed and destroyed over the last 4.6 billion years Altered due to physical, chemical, and biological processes Geologic cycle - group of cycles Tectonic, Hydrologic Rock Biogeochemical 11.1 Pangaea • Alfred Wegener was a German climatologist and arctic explorer who suggested the concept of continental drift. • Continental drift is the idea that the continents move around on Earth’s surface. 11.1 Movement of continents • Wegener thought that the continents we know today had once been part of an earlier supercontinent. • He called this great landmass Pangaea. 11.1 Movement of continents • The surface of Earth is broken into many pieces like a giant jigsaw puzzle. • Plate tectonics describes how these pieces move on Earth’s surface. 11.2 Sea Floor Spreading • American geophysicist Harry Hess helped develop the theory of plate tectonics. • While a Navy officer, Hess helped map the ocean floor. 11.2 What drives lithospheric plates? • Convection cells in Earth’s lower mantle drive the lithospheric plates on the surface. • Heated lower mantle material rises toward Earth’s surface. 11.3 Plate boundaries • • • Imagine a single plate, moving in one direction on Earth’s surface. One edge of the plate—the divergent boundary—moves away from things. The opposite edge—called the leading edge or convergent boundary bumps into anything in the way. 11.2 Hot spots and island chains • After the island forms, the movement of the plate carries it away from the mantle plume. • Scientists determine the direction and speed of plate movement by measuring these island chains. 11.2 Hot spots and island chains • A single hot rising plume, called a mantle plume, can cause a volcanic eruption in the plate above it. • If the eruption is strong and lasts long enough, the volcanic eruption may form an island on the plate. 11.3 Mountains and convergent boundaries • Mountain ranges are formed when continents collide. 11.3 Transform fault boundaries • • A good clue for locating transform faults is offsetting. When seen from above, the feature will appear to make a zig-zag. The Hydrologic Cycle The transfer of water from oceans to the atmosphere to the land and back to the oceans Driven by solar energy Evaporation of water from oceans Precipitation of water on land Transpiration of water by plants Evaporation of water from land Runoff from streams, rivers and subsurface groundwater The Hydrologic Cycle Total water on earth = 1.3 billion km3 97% in oceans 2% in glaciers and ice caps 0.001% in atmosphere The rest in fresh water on land The Hydrologic Cycle At the regional and local level, the fundamental unit of the landscape is the drainage basin The area that contributes surface runoff to a particular stream or river Vary greatly in size Usually named for main stream or river The Rock Cycle Consists of numerous processes that produce rocks and soils Depends of the tectonic cycle for energy and the hydrologic cycle for water Rocks classified as Igneous Sedimentary Metamorphic The Phosphorus Cycle P one of the “big six” required for life Often a limiting factor for plant and algal growth Does not have a gaseous phase Rate of transfer slow The Phosphorus Cycle Enters biota through uptake as phosphate by plants, algae and some bacteria Returns to soil when plants die or is lost to oceans via runoff Returned to land via ocean feeding birds (guano) Guano deposits major source of P for fertilizers Nutrient Cycles Cycling maintains homeostasis (balance) in the environment. •3 cycles to investigate: 1. Water cycle 2. Carbon cycle 3. Nitrogen cycle Water cycle•Evaporation, transpiration, condensation, precipitation Water cycle- Carbon cycle•Photosynthesis and respiration cycle carbon and oxygen through the environment. Carbon cycle- The Carbon-Silicate Cycle The cycling of carbon intimately involved with the cycling of silicon Weak carbonic acid falls as rain and weathers silicate rich rocks Releases Ca2+ and HCO3Transferred to oceans and used by marine animals to construct shells Shells deposited on sea floor become part of sed rock layer and return to surface in subduction zones The Carbon-Silicate Cycle Affects the levels of CO2 and O2 in the atmosphere Nitrogen cycleAtmospheric nitrogen (N2) makes up nearly 78%-80% of air. Organisms can not use it in that form. Lightning and bacteria convert nitrogen into usable forms. Nitrogen cycleOnly in certain bacteria and industrial technologies can fix nitrogen. Nitrogen fixation-convert atmospheric nitrogen (N2) into ammonium (NH4+) which can be used to make organic compounds like amino acids. N2 NH4+ Nitrogen cycleNitrogen-fixing bacteria: Some live in a symbiotic relationship with plants of the legume family (e.g., soybeans, clover, peanuts). Nitrogen cycle•Some nitrogen-fixing bacteria live free in the soil. •Nitrogen-fixing cyanobacteria are essential to maintaining the fertility of semi-aquatic environments like rice paddies. Lightning Atmospheric nitrogen Nitrogen Cycle Denitrification by bacteria Animals Nitrogen fixing bacteria Decomposers Ammonium Nitrification by bacteria Plants Nitrites Nitrates