The Earth System Flashcards
The Earth system is made up of four main “spheres”:
- Geosphere
- Hydrosphere
- Atmosphere
- Biosphere
Biogeochemical Cycles
- Matter is neither created nor destroyed, it is recycled
- The ingredients for life (CHNOPS) can be stored in one sphere for a period of time, but also naturally move from one sphere to another through chemical reactions or phase changes
- Movements between spheres = biogeochemical cycles
The water cycle, carbon cycle, and nitrogen cycle allow Earth to sustain life.
The Hydrologic Cycle
Transfer of water among the spheres
- Is not smooth and continuous, but a stop and go process
- Water is temporarily stored in one of several major reservoirs (atmosphere, vegetation, lakes, river, groundwater, oceans) before it is transferred to another
Water moves from reservoir to reservoir through several different processes:
- Evaporation
- Precipitation
- Runoff (surface only)
- Infiltration (into substrate)
- Transpiration (evaporation of water from plants at leaves)
- Groundwater flow
The sizes of reservoirs are variable and the rate of transfer between reservoirs depends on:
temperature, wind, relative humidity, etc.
The Carbon Cycle
Describes how carbon moves between the biosphere, geosphere, hydrosphere, and atmosphere
- Carbon we have on Earth has been here since Earth formed
- It has been recycled from one form to another over time
Carbon (C) is the building block of many molecules (CO2, glucose, ATP, etc.)
- If a decaying organism undergoes burial, it is protected from decomposition. The carbon from it then enters the geosphere instead of the atmosphere or biosphere. May turn into coal in a very long time with compaction.
- Best way to return carbon from coal = combustion of fossil fuels into atmosphere
- CO2 is also dissolved in the oceans, which can be used by organisms to construct skeletons/shells. Shells may dissolve and carbon will be returned to ocean or they can pile up on ocean floor and become limestone with burial and compaction which enters the geosphere
Carbon is temporarily stored in different reservoirs within each sphere and transferred to
other reservoirs through various processes
Just like water in the hydrologic cycle, the carbon cycle is a
stop and go process. Carbon is temporarily stored in several major reservoirs and the reservoirs vary in size.
Carbon reservoirs (from smallest to largest):
- Atmosphere
- Vegetation
- Soils
- Surface of the ocean
- Deep ocean
- Rocks and sediments
Which rock type stores most of the world’s carbon?
Carbonates (limestones, etc.) have more than coal
Carbon may form organic or inorganic compounds:
Organic carbon: hydrocarbons, often in long chains that are mostly made in living things:
- Proteins, carbohydrates, fats, DNA
Inorganic carbon: carbon not bonded to hydrogen; some are made by living things:
- CaCO3 (calcium carbonate)
- CO2
Which rock type is made up of organic carbon? Inorganic?
- Coal = organic carbon
- Carbonate rocks = inorganic
The Carbon Cycle allows organic carbon to become
inorganic carbon and vice versa. This allows carbon to be exchanged freely among all reservoirs.
Small surface reservoirs can exchange all of their C with one another in a few years, whereas deep ocean is
partially isolated by temperature differences; exchanges with surface ocean/atmosphere in >100 years.
C buried in seds and rock takes >1000 years to fully exchange.
Large fluxes are ~balanced year to year, which means that
C into a reservoir = C out of that reservoir
Processes leading to an increase in carbon in atmosphere (positive number):
volcanoes, fossil fuel burning, deforestation
Processes leading to a reduction in carbon in atmosphere (neg number):
carbonate rock formation, weathering
Scientific Models:
physical, mathematical, or conceptual representations of a system of ideas, events, or processes
- Are not reality, they are simplified versions of reality
Residence time
The length of time carbon stays in any given reservoir
the surface ocean is in direct contact with the atmosphere and exchanges carbon:
easily with the atmosphere. The deep ocean partially isolated by temperature differences; exchanges C with surface ocean/atmosphere in >100 years.
Carbon sinks
reservoirs that accumulate and store carbon for a long period of time
Carbonate rocks and the deep ocean are large reservoirs with long:
residence time and low fluxes. This means they are able to store carbon for long periods of time and are excellent carbon sinks.
Other Cycles
Although the processes, fluxes, and residence times vary, the other ingredients for life (S and P) also cycle through the Earth system
Rock Cycle
Large scale process that describes how one rock type becomes another when it enters a new tectonic environment
- Weathering and volcanism are two major processes that allow elements to exchange b/w the geosphere, hydrosphere, and atmosphere
- The rock cycle encompasses many biogeochemical cycles
Volcanism
Volcanic eruption allow gases (water carbon dioxide, sulfur dioxide) to move from geosphere to atmosphere
What is weathering?
- Breaking down rocks
- Earth materials are weather through: physical weathering and chemical weathering
- Earth materials are eroded by: wind, running water, waves, glaciers, groundwater, gravity
Physical weathering:
Mechanical breakdown of rocks into smaller pieces
- Frost wedging: water freezes in joints/cracks and expands
- Root wedging: roots push grains and rock fragments apart
- Ventifaction: blowing wind can sandblast rocks
- Thermal expansion: changes in temperature cause rocks to expand and contract
- Salt crystal growth: crystals grow in cracks and push grains and rock fragments apart
- Bioturbation: burrowing animals loosen aerate sediments, includes root wedging
Rates of physical weathering depend on:
- Local climatic/environment conditions
- Rock type, texture, structures
- Biological activity
- Time
Local climatic/environment conditions
- Seasonal temperature changes
- Seasonal fires
- Aridity (salt growth)
- Strong, persistent winds
- Water availability
Rock type, texture, structures
Some rock types are less resistant to weathering than others
Biological Activity
Burrowing animals and plants break rocks and churn sediments
Time
The longer a rock is exposed, the more it will be weathered
Chemical weathering:
alters rocks and minerals at Earth’s surface as they react with water, oxygen, and carbon dioxide. This produces new minerals, dissolved elements, and compounds.
4 main chemical processes lead to chemical weathering (not a complete list of course):
- Dissolution/Solution
- Oxidation
- Hydration
- Hydrolysis
Dissolution/Solution
Dissolving a mineral in water or a weak acid
- Acid rain/surface water produced when CO2, SO2, or NOx combine with water = H2O + CO2 -> H2CO3
- Acid dissolves carbonate rocks, creating solution of calcium and bicarbonate ions HCO3-
- Results in chemical weathering at surface and underground cave systems called karst
Karst Topography
- Remember: karsts extend into the landscape
- Loss of structural integrity and then it will eventually collapse
Speleothems
- Travertine: carbonate rock precipitated directly from solution
- Forms dripstones: Stalactites (from the ceiling down) and stalagmites (from the ground up)
- Although more resistant to chemical weathering, silicates are also subject to dissolution. Both granite obelisks are believed to have been carved 3.5k years ago.
What caused the difference in weathering?
Climate = NYC more moisture vs. Egypt super dry Pollution = NYC super high pollution means more CO2 and sulfur so it favours production of acid rain which weathers it
Oxidation
Occurs when minerals react with oxygen
- Leads to rusting and produces iron-oxide minerals like hematite
- Pyroxene, amphibole, magnetite, pyrite, and olivine are most susceptible to oxidation because they are high in iron -> mafic rocks are more likely to be weathered bc of high mineral content that’s susceptible
Hydration
Occurs when minerals combine with water, changing their structures
- Can be undone with heating, but heating can induce chemical and physical weathering
Hydrolysis
Complex weathering reaction that produces clays, an important mineral in soils
- The main chemical reaction that removes carbon from the atmosphere
Hydrolysis Reaction
- Commonly, potassium feldspar reacts with H+ and OH- ions in water to produce clay minerals, potassium and silica in solution
- When silicate rocks react with carbonic acid, a mixture of clay and dissolved ions are produced. The dissolved ions are carried by rivers to oceans, where they become incorporated into the shells of organisms
- If the shells accumulate on the sea floor and turn into stone, they enter into long-term carbon storage (VERY SLOW process)
Rate of chemical weathering controlled by:
- Surface environment (rocks under water or not)
- Exposed surface area (more surface area results in more chemical weathering)
- Grain size (related to surface area)
- Climate (more weathering in warm, humid climates)
- Nature of rocks and minerals (some rocks and minerals are more susceptible to weathering than others: granite vs. limestone, quartz vs. feldspar)
