geological cycles

1. Cycles and cycle models
The Biogeochemical Cycles

2. How Chemicals Cycle
• Biogeochemical Cycle
– The complete path a chemical takes through
the four major components – or reservoirs –
of Earth’s systems
1. Atmosphere
2. Hydrosphere
3. Lithosphere
4. Biosphere

3. Chemical Reactions
• Chemical reaction:
– The process in which new chemicals are
formed from elements and compounds
through chemical change

4. Biogeochemical Cycles and Life:
Limiting Factors
• Macronutrients
– Elements required in large amounts by all life
– Include the “big six” elements that form the fundamental building
blocks of life:
carbon oxygen
hydrogen phosphorus
nitrogen sulfur
• Micronutrients
– Elements required either in
• small amounts by all life or
• moderate amounts by some forms of life and not all by others
• Limiting factor
– When chemical elements are not available at the right times, in
the right amounts, and in the right concentrations relative to each
other

5. The Geologic Cycle
• The Geologic Cycle:
– The processes responsible for formation and
change of Earth’s materials
– Best described as a group of cycles:
• Tectonic
• Hydrologic
• Rock
• Biochemical

6. Tectonic Cycle
• Tectonic cycle:
– Involves creation and destruction of the solid
outer layer of Earth, the lithosphere
• Plate tectonics:
– The slow movement of these large segments
of Earth’s outermost rock shell
– Boundaries between plates are geologically
active areas

7. Tectonic Cycle: Plate
Boundaries
• Divergent plate boundary:
– Occurs at a spreading ocean ridge, where plates are
moving away from one another
– New lithosphere is produced (seafloor spreading)
• Convergent plate boundary
– Occurs when plates collide
• Produces linear coastal mountain ranges or continental
mountain ranges
• Transform fault boundary
– Occurs where one plate slides past another
• San Andreas Fault in California

8. The Hydrologic Cycle
• The Hydrologic Cycle:
– The transfer of water from the oceans to the
atmosphere to the land and back to the
oceans. Includes:
• Evaporation of water from the oceans
• Precipitation on land
• Evaporation from land
• Runoff from streams, rivers, and sub-surface
groundwater

9. The Rock Cycle
• The rock cycle:
– Numerous processes that produce rocks and
soils
– Depends on other cycles:
• tectonic cycle for energy
• Hydrologic cycle for water
– Rock is classified as
• Igneous
• Sedimentary
• Metamorphic

10. The Carbon Cycle
• Carbon is the element that anchors all
organic substances
• The carbon cycle:
– Carbon combines with and is chemically and
biologically linked with the cycles of oxygen
and hydrogen that form the major compounds
of life

11. Botkin & Keller
Environmental Science 5e

12. The Carbon-Silicate Cycle
• The carbon-silicate cycle:
– A complex biogeochemical cycle over time scales as
long as one-half billion years.
– Includes major geological processes, such as:
• Weathering
• Transport by ground and surface waters
• Erosion
• Deposition of crustal rocks
– Believed to provide important negative feedback
mechanisms that control the temperature of the
atmosphere.

13. The Nitrogen Cycle
• The nitrogen cycle:
– Cycle responsible for moving important nitrogen
components through the biosphere and other Earth
systems
– Extremely important because nitrogen is required by
all living things
• Nitrogen fixation:
– The process of converting inorganic, molecular
nitrogen in the atmosphere to ammonia or nitrate
• Denitrification:
– The process of releasing fixed nitrogen back to
molecular nitrogen

14. The Phosphorus Cycle
• The phosphorus cycle:
– Involves the movement of phosphorus
throughout the biosphere and lithosphere
– Important because phosphorus is an essential
element for life and often is a limiting nutrient
for plant growth.