1. Chapter 6: The Biogeochemical Cycles

2. Overview Earth is a Peculiar Planet Life and Global Chemical Cycles
General Aspects of Biogeochemical Cycles
The Geologic Cycle
Some Major Global Biogeochemical Cycles

3. Earth is a Peculiar Planet
Four unique characteristics:
Liquid water
Water at its triple point (all three phases)
Plate tectonics
Life!
Life has a large effect on biogeochemical cycling
Why does earth have life, and not the nearby planets?

4. 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

5. 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

6. 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

7. Rise of Oxygen
Evolution of Photosynthesis brought about gaseous oxygen
Photosynthesis - carbon dioxide and water are combined in presence of light to create sugars and free oxygen
Took 2 billion years before oxygen started to accumulate in atmosphere
First it oxidized all the unoxidized iron

8. Rise of Oxygen
Early photosynthesizers included stromatolites (3.4 billion years old)

9. Early organisms on earth
Prokaryotes
Simple cell structure
Lacked organelles and a nucleus (too much energy to maintain)
Get energy from fermentation
Low energy yield to organism
Waste products of carbon dioxide and alcohol
Live singly or on end-to-end chains
Cannot form 3-D structures

10. Early Organisms of Earth
Eukaryotes
Use oxygen for respiration (energy efficient)
Larger cells with nucleus and organelles
Form 3-D colony of cells
Permits multi-cellular body structure of plants, animals and fungi

11. 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

12. 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

14. Life and Global Chemical Cycles
For life to persist elements must be available at the right time, in the right amount, and in right concentrations relative to one another
Too much of some elements – can be toxic
Too little of some element – can limit growth and development
Neutral – some elements are neutral for life

15. 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

16. General Aspects of Biogeochemical Cycles
Some chemicals cycle quickly and are readily regenerated for biological activity
They typically have a gas phase, are soluble and carried by the hydrologic cycle
Oxygen and nitrogen
Other chemical elements are relatively immobile and returned by geological processes
Typically lack a gas phase and insoluble
Phosphorus

17. General Aspects of Biogeochemical Cycles
Most required nutrients are light
Heaviest is iodine with atomic weight of 53
Since life evolved it has altered biogeochemical cycles
The continuation of processes that control biogeochemical cycles essential for maintenance of life

18. General Aspects of Biogeochemical Cycles
Through modern technology transfer rate of elements into air, water, and soil altered
May benefit society, but may also pose environmental hazard
Must recognize the + and – consequences of altering cycles

19. General Aspects of Biogeochemical Cycles
Simplest way to view a cycle is a box and arrow diagram
Boxes represent places where a chemical is stored
Donating compartment is a source
Receiving compartment is a sink
Amount of time an atom spends in any compartment is called its residence time
Arrows represent pathways of transfer
Flow is the amount moving from one box to another
Flux is the rate of transfer

21. The Geologic Cycle Rocks and Soil Geologic cycle - group of cycles
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

23. The Tectonic Cycle
Involves creation and destruction of the lithosphere (outer layer of Earth)
~100 km thick and broken in to several plates
The slow movement of plates is called plate tectonics
2–15cm/yr
Plate tectonics has large scales effects
Location and size of continents
Alterations in climate
Ecological islands
Areas of volcanic activity and earthquakes

24. Types of Plate Boundaries
Divergent plate boundary
Occurs at a spreading ocean ridge, where plates moving away from one another
New lithosphere produced
Known as sea floor spreading, produces ocean basins
Convergent plate boundary
Occurs when plates collide
When heavier ocean plates meet lighter continental plates a subduction zone is present
When two lighter continental plates collide a continental mountain range may form

25. The Tectonic Cycle Transform fault boundary
Occurs where one plate slides past another
San Andreas Fault in California
Boundary of NA and Pacific plates
LA moving towards SF

27. 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

28. 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

29. 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

31. 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

33. The Rock Cycle
Physical weathering (freeze, thaw) produces sediment such as gravel, sand and silt.
Chemical weathering occurs when weak acids in water dissolve chemicals from rocks.

34. The Carbon Cycle
Carbon is the element that anchors all organic substances
Carbon has a gaseous phrase
Enters atmosphere (CO2 and CH4) through respiration, fires and diffusion
Removed from the atmosphere by photosynthesis

35. The Carbon Cycle Carbon occurs in the ocean in several forms
Dissolved CO2, carbonate and bicarbonate
Marine organisms and their products, CaCO3
Enters the ocean by
Simple diffusion then dissolves
Transfer from land in rivers as dissolved carbon
Wind

36. The Carbon Cycle
Carbon enters the biota through photosynthesis and then returned by respiration or fire
When organism dies decomposition releases carbon
If buried under certain conditions carbon is not be released
Transformed into fossil fuels

38. 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 HCO3-
Transferred 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

39. The Carbon-Silicate Cycle
Affects the levels of CO2 and O2 in the atmosphere

41. The Nitrogen Cycle
N essential to life because it is necessary for the production of proteins and DNA
Free N2 makes up 78% of atmosphere
But most organisms can’t use it directly
Relatively unreactive element must be converted to NO3- or NH4+
Performed by bacteria

42. The Nitrogen Cycle
Nitrogen fixation - process of converting atmospheric N to NO3- or NH4+
Denitrification - process of releasing fixed N back to molecular N
Almost all organisms depend on N converting bacteria
Some have formed symbiotic relationships in the roots of plants or stomach on animals

43. The Nitrogen Cycle
Industrial process can now convert molecular N into compounds usable by plants
Main component of N fertilizers
N in agricultural runoff potential source of water pollution
N combines with O at high temperatures
Oxides of N a source of air pollution

45. 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

46. 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

48. Sulfur Cycle