Unit 4 Earth Systems Apes Exam Review

Unit 4 Earth Systems APES Exam Review: A Comprehensive Guide to Success

Understanding the intricate workings of Earth's systems is crucial not only for scoring well on the AP Environmental Science (APES) exam but also for becoming an informed and responsible citizen of our planet. This comprehensive review of Unit 4, Earth Systems, will equip you with the knowledge and strategies necessary to tackle any question related to this foundational topic. We'll delve into the structure of the Earth, plate tectonics, soil composition, the atmosphere, the global water cycle, and much more, all with an eye towards the APES exam format.

The Foundation: Earth's Structure and Plate Tectonics

Before we can explore how Earth's systems interact, we need to understand the basic structure of our planet. The Earth is composed of several layers, each with unique characteristics:

• The Crust: The outermost layer, divided into oceanic and continental crust. Oceanic crust is thinner and denser than continental crust.
• The Mantle: A thick, semi-molten layer beneath the crust. Convection currents within the mantle drive plate tectonics.
• The Outer Core: A liquid layer composed primarily of iron and nickel.
• The Inner Core: A solid, dense sphere of iron and nickel.

Plate tectonics is the theory that Earth's lithosphere (the crust and the uppermost part of the mantle) is divided into several plates that move slowly over the asthenosphere (the partially molten layer within the mantle). This movement is responsible for many geological phenomena, including:

• Continental Drift: The gradual movement of continents over geological time.
• Seafloor Spreading: The formation of new oceanic crust at mid-ocean ridges.
• Subduction: The process where one tectonic plate slides beneath another.
• Earthquakes: Sudden releases of energy along faults (fractures in the Earth's crust).
• Volcanoes: Openings in the Earth's crust where molten rock (magma) erupts.
• Mountain Building: The collision of tectonic plates can create mountain ranges.

Key Plate Boundaries to Know:

• Divergent Boundaries: Plates move apart, allowing magma to rise and form new crust (e.g., mid-ocean ridges, rift valleys).
• Convergent Boundaries: Plates collide. This can result in subduction (oceanic plate under continental or oceanic plate) or mountain building (continental plate colliding with continental plate).
• Transform Boundaries: Plates slide past each other horizontally, causing earthquakes (e.g., San Andreas Fault).

APES Exam Tip: Understand the different types of plate boundaries and the geological events associated with each. Be prepared to analyze diagrams and maps showing plate boundaries and predict the resulting geological activity.

The Ground Beneath Our Feet: Soil Formation and Composition

Soil is a vital component of terrestrial ecosystems, supporting plant life and playing a crucial role in nutrient cycling. Understanding soil formation, composition, and properties is essential for APES.

Soil Formation:

Soil is formed through the weathering of rocks and the decomposition of organic matter. The process of soil formation is influenced by several factors:

• Parent Material: The underlying rock from which the soil is derived.
• Climate: Temperature and precipitation affect weathering rates and the decomposition of organic matter.
• Topography: Slope and aspect (direction a slope faces) influence erosion and water drainage.
• Organisms: Plants, animals, and microorganisms contribute to the decomposition of organic matter and nutrient cycling.
• Time: Soil formation is a slow process that can take thousands of years.

Soil Composition:

Soil is composed of:

• Minerals: Weathered rock fragments (sand, silt, and clay).
• Organic Matter: Decomposed plant and animal remains (humus).
• Water: Held in pore spaces between soil particles.
• Air: Also held in pore spaces, providing oxygen for plant roots and soil organisms.

Soil Horizons:

Soil is typically organized into distinct layers called horizons. The main horizons are:

• O Horizon: The uppermost layer, composed of organic matter (leaf litter, humus).
• A Horizon: The topsoil layer, a mixture of minerals and organic matter. This is the most fertile layer.
• E Horizon: A layer of leaching, where minerals are dissolved and carried downwards.
• B Horizon: The subsoil layer, where minerals leached from the E horizon accumulate.
• C Horizon: Weathered parent material.
• R Horizon: Bedrock.

Soil Properties:

• Texture: The proportion of sand, silt, and clay in the soil. Soil texture affects water drainage, aeration, and nutrient retention.
• Porosity: The amount of pore space in the soil.
• Permeability: The rate at which water flows through the soil.
• pH: A measure of the acidity or alkalinity of the soil. Soil pH affects nutrient availability.
• Nutrient Content: The amount of essential nutrients (nitrogen, phosphorus, potassium, etc.) in the soil.

Soil Degradation:

• Erosion: The removal of topsoil by wind or water.
• Compaction: The compression of soil particles, reducing porosity and permeability.
• Salinization: The accumulation of salts in the soil, often due to irrigation.
• Nutrient Depletion: The removal of nutrients from the soil by crops.

APES Exam Tip: Be able to describe the soil formation process, identify the different soil horizons, and explain how soil properties affect plant growth and environmental quality. Understand the causes and consequences of soil degradation.

The Blanket of Air: Earth's Atmosphere

The atmosphere is a layer of gases that surrounds the Earth, providing essential functions such as regulating temperature, protecting us from harmful radiation, and supporting life.

Atmospheric Layers:

The atmosphere is divided into several layers based on temperature gradients:

• Troposphere: The lowest layer, where weather occurs. Temperature decreases with altitude.
• Stratosphere: Contains the ozone layer, which absorbs harmful UV radiation. Temperature increases with altitude.
• Mesosphere: Temperature decreases with altitude.
• Thermosphere: Temperature increases with altitude.
• Exosphere: The outermost layer, where the atmosphere gradually merges with space.

Atmospheric Composition:

The atmosphere is primarily composed of:

• Nitrogen (N2): Approximately 78%
• Oxygen (O2): Approximately 21%
• Argon (Ar): Approximately 0.9%
• Other Gases: Including carbon dioxide (CO2), methane (CH4), and water vapor (H2O).

The Greenhouse Effect:

Certain gases in the atmosphere, known as greenhouse gases, trap heat and warm the Earth. This is a natural process that is essential for life on Earth. However, increased concentrations of greenhouse gases due to human activities are enhancing the greenhouse effect, leading to global warming.

Greenhouse Gases:

• Carbon Dioxide (CO2): Released by burning fossil fuels, deforestation, and industrial processes.
• Methane (CH4): Released by livestock, natural gas leaks, and decomposition in landfills.
• Nitrous Oxide (N2O): Released by agricultural activities and industrial processes.
• Chlorofluorocarbons (CFCs): Synthetic compounds formerly used in refrigerants and aerosols. CFCs deplete the ozone layer.
• Water Vapor (H2O): A natural greenhouse gas that is influenced by temperature.

Ozone Depletion:

The ozone layer in the stratosphere absorbs harmful UV radiation. CFCs and other ozone-depleting substances have thinned the ozone layer, increasing the amount of UV radiation reaching the Earth's surface.

Air Pollution:

The introduction of pollutants into the atmosphere can have harmful effects on human health and the environment.

• Primary Pollutants: Pollutants emitted directly from a source (e.g., sulfur dioxide from burning coal).
• Secondary Pollutants: Pollutants formed in the atmosphere through chemical reactions (e.g., ozone from the reaction of nitrogen oxides and volatile organic compounds).

Major Air Pollutants:

• Particulate Matter (PM): Tiny particles that can be inhaled and cause respiratory problems.
• Ozone (O3): A respiratory irritant and a major component of smog.
• Sulfur Dioxide (SO2): Contributes to acid rain and respiratory problems.
• Nitrogen Oxides (NOx): Contributes to smog, acid rain, and respiratory problems.
• Carbon Monoxide (CO): A toxic gas that can reduce oxygen delivery to the body.
• Lead (Pb): A neurotoxin that can impair brain development.

APES Exam Tip: Understand the structure and composition of the atmosphere, the greenhouse effect, ozone depletion, and the causes and effects of air pollution. Be able to discuss strategies for reducing greenhouse gas emissions and air pollution.

The Lifeblood of the Planet: The Global Water Cycle

Water is essential for all life on Earth. The global water cycle describes the continuous movement of water between the oceans, atmosphere, and land.

Key Processes in the Water Cycle:

• Evaporation: The process by which liquid water changes into water vapor.
• Transpiration: The release of water vapor from plants.
• Condensation: The process by which water vapor changes into liquid water, forming clouds.
• Precipitation: Water falling from the atmosphere to the Earth's surface as rain, snow, sleet, or hail.
• Infiltration: The process by which water soaks into the ground.
• Runoff: Water that flows over the land surface.

Water Reservoirs:

• Oceans: The largest reservoir of water on Earth.
• Ice Caps and Glaciers: Store a significant amount of fresh water.
• Groundwater: Water stored underground in aquifers.
• Lakes and Rivers: Surface water bodies.
• Atmosphere: Contains water vapor.

Human Impacts on the Water Cycle:

• Deforestation: Reduces transpiration and increases runoff.
• Urbanization: Increases runoff and reduces infiltration.
• Irrigation: Depletes groundwater resources.
• Pollution: Contaminates water supplies.
• Climate Change: Alters precipitation patterns and increases evaporation rates.

Water Scarcity:

Water scarcity is a growing problem in many parts of the world due to increasing demand and limited supplies.

APES Exam Tip: Be able to describe the processes involved in the water cycle, identify the major water reservoirs, and explain how human activities impact the water cycle. Understand the causes and consequences of water scarcity.

Biogeochemical Cycles: Connecting Life and Earth

Biogeochemical cycles describe the movement of essential elements (carbon, nitrogen, phosphorus, sulfur) through the biotic (living) and abiotic (non-living) components of the Earth's systems. Understanding these cycles is crucial for understanding how ecosystems function and how human activities can disrupt them.

The Carbon Cycle:

Carbon is the building block of all organic molecules. The carbon cycle involves the movement of carbon between the atmosphere, oceans, land, and living organisms.

• Photosynthesis: Plants absorb carbon dioxide from the atmosphere and convert it into organic compounds.
• Respiration: Organisms release carbon dioxide into the atmosphere as they break down organic compounds.
• Decomposition: Decomposers break down dead organisms and release carbon dioxide into the atmosphere and soil.
• Combustion: Burning fossil fuels and biomass releases carbon dioxide into the atmosphere.
• Ocean Uptake: The ocean absorbs carbon dioxide from the atmosphere.

Human Impacts on the Carbon Cycle:

• Burning Fossil Fuels: Increases the concentration of carbon dioxide in the atmosphere.
• Deforestation: Reduces the amount of carbon dioxide absorbed by plants.

The Nitrogen Cycle:

Nitrogen is an essential nutrient for plant growth. The nitrogen cycle involves the conversion of nitrogen gas (N2) into forms that plants can use.

• Nitrogen Fixation: The conversion of nitrogen gas into ammonia (NH3) by bacteria.
• Nitrification: The conversion of ammonia into nitrite (NO2-) and nitrate (NO3-) by bacteria.
• Assimilation: Plants absorb nitrate and ammonia and incorporate them into organic molecules.
• Ammonification: Decomposers break down dead organisms and release ammonia into the soil.
• Denitrification: The conversion of nitrate into nitrogen gas by bacteria.

Human Impacts on the Nitrogen Cycle:

• Fertilizer Use: Increases the amount of nitrogen in the soil, leading to water pollution.
• Burning Fossil Fuels: Releases nitrogen oxides into the atmosphere, contributing to acid rain and smog.

The Phosphorus Cycle:

Phosphorus is an essential nutrient for plant growth and is a component of DNA and ATP. The phosphorus cycle is a slow cycle that does not involve the atmosphere.

• Weathering: Weathering of rocks releases phosphate into the soil.
• Assimilation: Plants absorb phosphate from the soil.
• Decomposition: Decomposers break down dead organisms and release phosphate into the soil.
• Sedimentation: Phosphate can be transported to the ocean and incorporated into sediments.
• Uplift: Geological uplift can bring phosphate-rich sediments back to the land surface.

Human Impacts on the Phosphorus Cycle:

• Mining Phosphate Rock: Increases the amount of phosphorus available for use as fertilizer.
• Fertilizer Use: Increases the amount of phosphorus in the soil, leading to water pollution.

The Sulfur Cycle:

Sulfur is a component of proteins and is important for plant growth. The sulfur cycle involves the movement of sulfur between the atmosphere, oceans, land, and living organisms.

• Weathering: Weathering of rocks releases sulfur into the soil.
• Volcanic Eruptions: Release sulfur dioxide into the atmosphere.
• Decomposition: Decomposers break down dead organisms and release sulfur into the soil.
• Assimilation: Plants absorb sulfate from the soil.

Human Impacts on the Sulfur Cycle:

• Burning Fossil Fuels: Releases sulfur dioxide into the atmosphere, contributing to acid rain.
• Mining: Releases sulfur from underground deposits.

APES Exam Tip: Be able to describe the major biogeochemical cycles (carbon, nitrogen, phosphorus, sulfur) and explain how human activities are impacting these cycles. Understand the consequences of disrupting these cycles.

Conclusion: Mastering Earth Systems for APES Success

This comprehensive review has covered the major concepts within Unit 4: Earth Systems. By understanding the structure of the Earth, plate tectonics, soil composition, the atmosphere, the global water cycle, and biogeochemical cycles, you'll be well-prepared to tackle any question on the APES exam. Remember to focus on the interactions between these systems and the impacts of human activities. Good luck with your studying! Remember to practice with past APES exam questions to solidify your understanding.