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Terrestrial Biogeochemistry

Terrestrial Biogeochemistry. The study of the biological, geological and chemical factors that control the distribution and abundance of elements on land. Introduction - Chapter 1. Studying the earth system is complicated --large spatial and temporal scales --feedback effects

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Terrestrial Biogeochemistry

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  1. Terrestrial Biogeochemistry The study of the biological, geological and chemical factors that control the distribution and abundance of elements on land

  2. Introduction - Chapter 1 Studying the earth system is complicated --large spatial and temporal scales --feedback effects --no true replication …but we do the best we can --plot-scale experimental work --regional scale studies --modeling to extrapolate in space and time --remote sensing of major earth processes

  3. Introduction - Chapter 1 Fluctuations are the KEY to most element cycles

  4. Finzi Teaches First Biogeochemistry Course Finzi Graduates High School Finzi Born

  5. Source: Luthi et al. (2008) Nature 453:379-382

  6. Source: Pearson and Palmer (2000). Nature 406:695-699

  7. QUIZ • What links obesity in America to annual fish kills in the Gulf of Mexico? • What do the deserts of Asia and the wet tropical forests of Hawaii share in common? • If you wanted to reduce the concentration CO2 in the Earth’s atmosphere, what the best long-term storage reservoir?

  8. Origins - Chapter 2 Six elements constitute 95% of mass of biosphere (i.e. living organisms) --C, H, N, O, P and S 20 Other elements are critical to life All elements have mass < iodine (atomic mass 53) --Life is driven by “light” elements

  9. Origins - Chapter 2 Origins of the Elements What is the distribution of elements in our solar system? (1) Except for Li, Be, and B, light elements (atomic number <30) are more abundant than heavy elements; (2) Elements with even AN are more abundant than odd AM (Figure 2.1) How did these elements form? “Big Bang” ~13.7 Billion Years Ago (BYA) Fusion of “quarks” into protons (1H) and neutrons And…fusion of protons and neutrons to form simple atoms: 2H, 4He,

  10. Origins - Chapter 2 Origins of the Elements What is the distribution of elements in our solar system? (1) Except for Li, Be, and B, light elements (atomic number <30) are more abundant than heavy elements; (2) Elements with even AN are more abundant than odd AM (Figure 2.1) How did these elements form? “Big Bang” ~13.7 Billion Years Ago (BYA) Fusion of “quarks” into protons (1H) and neutrons And…fusion of protons and neutrons to form simple atoms: 2H, 4He,

  11. Origins - Chapter 2 But…temperature and pressure ↓ declined rapidly …formation of heavier elements could not occur ……until the formation of stars (>1 BY) Stars: whirling clouds of gas and dust Core: Hydrogen “burning”2H + 2H → 4He As star ages, H is consumed, star collapses inward under own gravity…

  12. Origins - Chapter 2 Collapse ↑ core temperature and pressure Resulting in He burning…which generates carbon! 4He + 4He ↔ 8Be (unstable, rapid decay) 8Be + 4He → 12C But also… 4He + 12C → 16O OXYGEN! & 12C + 12 C → 24Mg MAGNESIUM! Which can decay to… 24Mg → 20Ne + 4He (alpha particle)

  13. Origins - Chapter 2 Planetary “formation” model explains elements up to AM of Fe (= 55.9) … but a star core dominated by Fe won’t burn, causing a supernova (catastrophic collapse and explosion) Elements w/AM > Fe formed by capture of successive neutrons by Fe which requires LOTS of energy National Radio Astronomy Observatory produced this series of images showing SN1993J as it expands to a diameter of 1/10th of a light year in 18 months

  14. Origins - Chapter 2 Collectively this model explains: • Logarithmic ↓ in abundance of elements after H and He (original building blocks) --3 Phases Big Bang (H, He) Core Burning (C-Fe) Supernova – Fusion (AM>Fe=56) 2. Even AM elements are more abundant than odd AM elements -- Formation of all elements beyond Li is based on fusion of nuclei with even number of atomic mass --Odd AM elements formed by fission of heavier elements and they are less stable 16O + 16O → 32S → 31P + 1H

  15. Origins - Chapter 2 Why are Li, Be and B in such low cosmic abundance? Initial fusion reactions pass over nuclei of AM 5 and skip to elements with even AM>8; Li, B, Be are formed by spallation—fission of heavier elements that are hit by cosmic rays in interstellar space!

  16. Origins - Chapter 2 Origin of the Solar System and the Earth Our galaxy is ~12.5 billion years old Our solar system is ~4.6 billion years -- the remnants of a supernova; -- all material is derived from “planetesimals” formed by the coalescence of dust and small bodies; -- each planet is unique because it is derived from different portions of the solar nebula.

  17. Inner Planets Sun Mercury Venus Earth Mars ‘hot’ portions of solar nebula Mercury Outer Planets Jupiter Saturn Uranus Neptune Pluto ‘cool’ portions of solar nebula

  18. Origins - Chapter 2 “Inner” planets formed in “hot” areas of solar nebula; “Outer” plants formed in “cool” areas of the solar nebula. Mercury (“inner”) dominated by Fe and other elements formed at high temp; high bulk density 5.4g cm-3 VS. Jupiter (“outer”) dominated H and He (BD = 1.25 g cm-3) w/overall composition same as cosmic abundance of elements Earth (“inner”) dominated by silicate materials due to intermediate temperatures (BD = 5.5 g cm-3); low abundance of light elements relative to solar abundance.

  19. What is the elemental composition of the earth? --Analysis of total vs. crustal composition suggests differentiation Percent

  20. Percent

  21. Origins - Chapter 2 What is the distribution of elements on the earth? --Analysis of crustal composition vs. total elemental composition suggests differentiation (Figure 2.3) Theories: Homogenous Accretion: 1. All elements arrived early in formation (~100MY); 2. NRG—collision of planetesimals and radioactive decay—melts Fe, Ni etc…and form magma; 3. Density separation of elements - Heavy core, light crust; 4. As earth cools lighter elements solidify on surface (Figure 2.4)

  22. Origins - Chapter 2 Heterogeneous Accretion: 1. Planetesimals and other materials not consistent through earths formation. --Core constituents arrived earlier than mantle 2. Late arrival of light elements in carbonaceous chondrites Which theory is correct? Well, not mutually exclusive… but late veneer of light elements seems probable 20Ne can provide some clues… -Noble gas, no reaction w/crust (…no transformation) -Too heavy to leave atmosphere (…no losses) -Not product of radioactive decay (…no/low rate of new input) …abundance of 20Ne in atm. today ≈ abundance in solar cloud

  23. Origins - Chapter 2 Assume other elements were delivered simultaneously, then Mass of Element Z = Qty of Z in Solar Cloud x Qty 20Ne on Earth on Earth Qty of 20Ne in Solar Cloud Consider the 14N: Ratio of 14N/20Ne in Solar Cloud = 0.91 Mass of 20Ne on Earth = 6.5 x 1016g Predict: 5.9 x 1016g N Observe: 39 x 1020g N …suggesting a heterogeneous accumulation of N on Earth!

  24. A tentative chronology of the Earth’s accretion. F Albarède Nature461, 1227-1233 (2009) doi:10.1038/nature08477 Chronometers shown in brown. Accretion of planetary material was interrupted by energetic electromagnetic radiation (T Tauri phase) sweeping across the disk within a few Myr of the isolation of the solar nebula. Runaway growth of planetesimals produces Mars-sized planetary embryos, which, collision after collision, form the planets with their modern masses. The last of these 'giant' collisions left material orbiting the Earth that later reassembled to form the Moon. The 182Hf–182W chronometer dates metal–silicate separation. The identical abundance of radiogenic 182W between the Earth and the Moon indicates that either the Moon formed after all the short-lived 182Hf had disappeared (>60 Myr) or, rather, the Moon-forming impact and terrestrial core segregation took place simultaneously 30 Myr after isolation of the solar nebula. Addition of a late veneer of chondritic material coming from beyond 2.5 au provides a strong explanation for the modern abundances of siderophile and volatile elements in the terrestrial mantle. This material also contained water and other volatile elements, which account for the origin of the terrestrial ocean. Such a model indicates that most of the terrestrial Pb and Xe was delivered by the asteroids that constituted the late veneer, and therefore that the young Pb–Pb and I–Xe ages of the Earth date, not the Earth, but events that affected the asteroids. It is suggested here that these events are those of the accretion to the Earth of the late veneer.

  25. Origins - Chapter 2 Origins of Atmosphere and Oceans Atmosphere: Carbonaceous chondrites major sources of C and N 0.5 – 3.6 % Carbon 0.01 – 0.28% Nitrogen Comets likely sources of C,N, H, O and other volatiles Meteors inputs in 1st billion years accounts for earths mass Early Atmospheric Composition --Most volatiles degassed from rocks delivered to mantle --Volcanoes emit light elements  degassing ongoing --H2O, CH4, SO2, HCl, CO2, N2

  26. Origins - Chapter 2 Oceans: When Earth hot (>100 oC) volatiles in atmosphere. As Earth’s surface cooled (<100 oC)….water started to condense and form the OCEANS …one h e l l of a rainstorm… Liquid water ever since 3.8 BYA. Atmospheric gases enter into primitive ocean (Henry’s Law): CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- HCl + H2O ↔ H3O+ + Cl- SO2 + H2O ↔ H2SO3

  27. Origins - Chapter 2 Gas solubility  early on atm. dominated by N2 CO2 1.4 g/L HCl 700 g/L VS. N2 0.018 g/L SO2 94.1 g/L Early composition of ocean is difficult to know… --substantial qty. of Cl- (like today) --dissolution of CO2 & HCl produce acids and “weather” crust releasing cations (Na+, Mg2+, Ca2+) --oceans accumulate cations until formation of precipitates CaCO3 dominant marine sediment for BYs …suggesting that Earth’s early oceans similar to that today.

  28. Origins - Chapter 2 Origin of Life • Reduced atm  abiotic synthesis of OC; • Carbonaceous chondrites contain simple OC and AA; • Clay minerals—surface charge and repeating structure—“string” together OC……RNA……proteins…abiotically; • Polarity of organics forms coacervates in H20…simple membranes; • In lab, organic molecules self replicate…although replicating, metabolizing, membrane bound structures not yet produced ……but given billions of years… • Science 9 January 2009, Vol. 323. no. 5911, pp. 198 – 199, DOI: 10.1126/science.323.5911.198 Apparatus used in the original Miller (1957) experiment

  29. Origins - Chapter 2 Origin of Metabolic Pathways 3.8 BY old rocks contain fossil bacteria…oldest known life…evolved in the sea Early heterotrophs…(today’s methanogens?) CH3COOH → 2CO2 + CH4 (Acetate) (Methane) N is a key component of biochemistry yet little availability N (e.g. NO3-) in seawater Origin of N2 fixation 2.2-3.5 BYA N2 + 8H+ + 8e- + 16ATP → 2NH3 + H2 + 16ADP + 16Pi -- N≡N requires 226kcal/mol energy to break triple bond -- low solubility of N2 in H2O Today N fixation coupled to photosynthesis  Cynaobacteria (marine) Symbiosis w/plants (terrestrial)

  30. Origins - Chapter 2 ...early heterotrophy inefficient given abiotic source of organic cmpds Strong selective pressure for autotrophy… 1st Photosynthesis S-based (lower NRG of reaction, but limited S in oceans) CO2 + 2H2S → CH20 + 2S + H20 …probably soon thereafter, O2-based PS CO2 + H2O → CH20 + 02 + H20 sunlight sunlight

  31. Origins - Chapter 2 Isotopic evidence for Ps (both S based / O2 evolving) - 13CO2 less reactive than 12CO2 - physical < biological discrimination, both present Standard for C = “Pee Dee” Belemnite, South Carolina - Carbonates less depleted in 13C, 0 – 2 ‰ - Carbohydrates greatly depleted in 13C, ~20 ‰ (Overhead 2.6)

  32. Origins - Chapter 2 Evidence for O2 releasing Ps only 1. Banded Iron Formations 3.5 – 2.0 BYA -Fe2+ in sea  Fe2O3 & S2-… - no free O2 in the atmosphere 2. Red Beds (transient atm. O2) 2.0 - Present -FeS2 on land oxidized -bands of Fe2O3 alternates w/other continental elements 3. Accumulation in atm - Ps > O2 consumption (Figure 2.7)

  33. A banded iron formation from the 3.15 BY old Moories Group, Barberton Greenstone Belt, South Africa. Red layers represent the times when oxygen was available, gray layers were formed in anoxic circumstances.

  34. Origins - Chapter 2 Free O2 in atmosphere fundamental change to earth Oxidizing agent in atmosphere (e.g. O3 in stratosphere and UV) Rapid evolution Eukaryotes diverge from prokaryotes ~2BYA (end of B.I.F.) Respiration in mitochondria efficient metabolism Ps now in specialized chloroplasts…more efficient Evolution of new biochemical pathways “Chemoautotrophy” (protons coupled to CO2 reduction) Nitrification 2NH4+ + 3O2→ 2NO2- + 2H20 + 4H+ 2NO2- + O2 → 2NO3-

  35. Origins - Chapter 2 …evolution of aerobic N transformations allow evolution of anaerobic N transformations… Denitrification: (anaerobic…microsites) 5CH2O + 4H+ + 4NO3-→ 2N2 + 5CO2 + 7H2O

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