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Chapter 9. Components of the Earth’s Environment

Recommended post: 【Earth Science】 Table of Contents for Earth Science

1. Overview

2. Atmosphere

3. Hydrosphere

4. Lithosphere

5. Biosphere

1. Overview

⑴ Earth System

① Types of Systems

○ Type 1. Isolated System: No movement of matter and energy

○ Type 2. Closed System: Movement of energy but no movement of matter

○ Type 3. Open System: Both movement of matter and energy exist

② Earth’s environment can be considered an open system

⑵ Components of the Earth’s Environment

① Each element constituting the Earth’s environment is independent and interacts with each other

② Components of the Earth’s environment: Atmosphere, Hydrosphere, Lithosphere, Biosphere

③ Interactions between components

Table 1. Interactions between Components of the Earth’s Environment

2. Atmosphere

⑴ Atmosphere

① Layer of atmosphere surrounding the Earth at about 1,000 km altitude

② Composed of troposphere, stratosphere, mesosphere, and thermosphere

③ Upper boundary of the atmosphere is not well-defined: Hydrogen is distributed up to about 10,000 km

⑵ Troposphere

① Extends from the surface to about 11 km

② Factors affecting tropospheric temperature are mainly terrestrial radiation

③ Temperature decreases as altitude increases due to decreasing terrestrial radiation, causing instability

④ Instability leads to vigorous convection movements in the atmosphere

⑤ Temperature lapse rate: 6.5 ℃ / km

⑥ Tropopause: Boundary between troposphere and stratosphere

○ Tropopause height increases with lower latitudes due to vigorous convection

○ Tropopause height is higher during summer than winter due to more active convection

○ Equator: 17.5 km

○ Mid-latitudes: 11.5 km

○ Polar regions: 7.5 km

⑶ Stratosphere

① Presence of ozone layer: 20 ~ 30 km, 2 ~ 8 ppm

② Ozone layer absorbs harmful ultraviolet radiation from the Sun

③ Temperature increases with altitude due to high absorption of UV radiation: Stable atmosphere

④ Stability leads to the absence of convection movements

⑤ Absence of convection creates a stable route for prolonged aircraft flight

⑷ Mesosphere

① Factors affecting mesospheric temperature are mainly terrestrial radiation

② Temperature decreases as altitude increases due to decreasing terrestrial radiation, causing instability

③ Instability leads to vigorous convection movements

④ Despite vigorous convection, lack of water vapor prevents weather phenomena

⑤ Coldest region in the atmosphere

⑥ Almost no oxygen

⑸ Thermosphere

① Very high altitudes, air density is extremely low, temperature varies significantly due to space heat sources

② Temperature increases with altitude due to proximity to the Sun

③ Large temperature variation due to direct absorption of solar energy, resulting in strong diurnal changes

④ Aurora occurs due to external radiation

○ N < C < … < He < H

⑹ Exosphere: Spans from about 60 km to 500 km

① Overlaps with the stratosphere, mesosphere, and thermosphere

② Air molecules ionized by X-rays and ultraviolet radiation from the Sun in this region

○ Ions and free electrons distributed in the atmosphere

○ Bohr atom model: Electrons absorb energy and are emitted, forming ions

③ Divided into D, E, and F layers based on electron density

Figure 1. Ionospheric Layers

○ D layer: About 60 km ~ 80 km, long-wave reflection, daytime

○ E layer: About 100 km ~ 120 km, medium-wave reflection

○ F₁ layer: About 170 km ~ 230 km, short-wave reflection, daytime

○ F₂ layer: About 200 km ~ 500 km, short-wave reflection

○ Daytime: E layer, F layers

○ Nighttime: D layer, E layer, F1 layer, F2 layer

④ Roles

○ Role 1: Blocks ground waves

○ Role 2: Blocks external waves, higher altitudes block more energy from outside

○ Long-distance communication medium

⑺ Homosphere: Within about 80 km. Gas is uniform due to convection and mixing interactions. Extends up to mesosphere

① Dry air

○ Air excluding water vapor

○ Nitrogen (78%): Essential element for plant growth (cf. nitrogen, phosphorus, potassium)

○ Oxygen (21%): Important element for respiration and combustion in plants and animals

○ Argon (0.9%)

○ Carbon dioxide (0.03%)

② Gases that vary with time and location

○ Water vapor

○ Main cause of weather changes

○ Important in Earth’s heat balance through heat energy transport

○ Carbon dioxide (CO₂)

○ Decreases due to plant photosynthesis

○ Increases due to emissions from Earth’s interior, industrial and vehicle emissions, respiratory activity of organisms, oceanic carbonates

○ Controlled by oceans

○ Major contributor to global warming

○ Ozone

○ Concentrated around 20 ~ 30 km

○ Absorbs ultraviolet radiation

○ Methane (CH₄)

○ Increases due to livestock grazing, microbial methane production in terrestrial environments

⑻ Heterosphere: Within about 80 km to 1,000 km. Gas is uneven due to sparse density and diffusion. Begins in thermosphere

① Distribution of gases in the atmosphere: Heavier gases lower, lighter gases higher

② Hydrogen at 1,000 km

③ Helium at 600 ~ 1,000 km

④ Oxygen at 300 ~ 600 km

⑤ Nitrogen at 200 ~ 300 km

⑼ Karman Line

① Boundary defined by physicist Theodore von Kármán between Earth’s atmosphere and outer space

② Defined at 100 km altitude: However, there are claims to lower it to 80 km

3. Hydrosphere

⑴ Components of the Hydrosphere

① Natural water = Seawater (97.22%) + Freshwater (2.78%)

② Components of freshwater

○ Freshwater = Glaciers and ice sheets (1.91%) + Groundwater (0.84%) + Others (0.03%)

○ Rainwater dissolves minerals on land, resulting in high CO₃^2- and Ca²⁺ content

③ Components of seawater

○ Composition of salt

○ Weathering and erosion of rocks

○ Submarine volcanoes: Highest concentration of Cl^- due to underwater volcanic eruptions

○ Absence of CO₃^2- and Ca²⁺ in seawater compared to freshwater due to biological utilization

○ 6 major elements in seawater (by mass)

○ Chloride ions (Cl^-): 55.0%

○ Sodium ions (Na⁺): 30.6%

○ Sulfate ions (SO₄^2-): 7.7%

○ Magnesium (Mg²⁺): 3.7%

○ Calcium (Ca²⁺): 1.2%

○ Potassium (K⁺): 1.1%

○ Element distribution in seawater (molar concentration)

Table 2. Element Distribution in Seawater

○ Variation in salinity according to latitude

○ Equator: Precipitation > Evaporation, low salinity

○ Mid-latitudes: Evaporation > Precipitation, high salinity

○ Polar regions: Intense ice melting, low salinity

○ Salinity of South Korea’s seas

○ Yellow Sea has lower salinity than East Sea: Yellow Sea is surrounded by land and has characteristics of freshwater

○ Salinity is lower in summer than winter: High precipitation - evaporation ratio in summer

○ Law of Constant Proportions of Salinity

Table 3. Law of Constant Proportions of Salinity

○ Mechanism: Mixed over long periods

○ Ion residence time

Figure 2. Ion Residence Time

○ Useful minerals extracted from seawater: Salt, magnesium, bromine, etc.

○ Gases dissolved in seawater: Oxygen, carbon dioxide, nitrogen, essential for marine life survival

⑵ Vertical Structure of Seawater: Differentiated by water temperature changes with depth

Figure 3. Division of Oceanic Layers

① Mixed Layer: 50 m ~ 200 m

○ Defined by a constant temperature in the vertical structure

○ Influenced by solar energy and wind: Wind-induced mixing maintains constant temperature

○ Thickens in winter: Cooling of surface water due to density currents increases the thickness of the mixed layer

○ Thickest at mid-latitudes: Strongest winds at mid-latitudes (due to atmospheric circulation)

○ Low concentration of carbon dioxide due to photosynthesis

② Thermocline: 200 m ~ 1,000 m

○ Defined by a rapid decrease in water temperature with increasing depth

○ Influenced by solar energy and wind: Less influence by wind

○ Stable: Lower layer always colder than upper layer, preventing convection

③ Deep Layer: 1,000 m ~

○ Definition: Zone with almost no temperature change below the thermocline layer.

○ Solar energy influence: No, Wind influence: No

○ Consistent water temperature regardless of latitude or season: 2 ~ 4 ℃. Density is highest at 4 ℃, but maximum density temperature varies under high-pressure situations.

○ Very low water temperature. High density. Low salinity.

○ Increased dissolved oxygen concentration due to cold subsurface seawater at high latitudes.

⑶ Seafloor Topography

Figure 4. Seafloor Topography

① Continental Shelf: Gentle slope with depth less than 200 m, near land.

○ Near the continent.

② Continental Slope: Extends seaward from the continental shelf.

○ Steep gradient.

○ Downwelling currents primarily occur here.

③ Trench: Deep trench with depth over 6,000 m.

④ Abyssal Plain: Broad, flat seafloor terrain at depths of about 3,000 m to 6,000 m.

⑤ Seamount: Underwater mountain rising from the ocean floor, pushed up by rock beneath.

○ Heat flux increases closer to seamount.

○ Thickness increases farther from seamount.

○ Over time, points on tectonic plates move away from seamount.

○ Thermoclines develop dominantly.

⑥ Volcanic Island: Island formed by accumulation of underwater volcanic eruptions.

⑦ Seaknoll: Conical peak rising from the ocean floor.

⑧ Guyot: Flattened top of a submerged volcanic peak due to erosion from waves.

⑨ Continental Rise: Gradual sloping area extending from the continental slope to the deep seafloor.

4. ** **Lithosphere (rock sphere)

⑴ Methods of Earth’s Interior Investigation: Include drilling, volcanic eruption analysis, seismic wave analysis, etc.

① Drilling Method

② Volcanic Eruption Analysis

③ Seismic Wave Analysis

○ Seismic Waves: Waves generated by earthquakes observed by seismometers.

○ Characteristic 1: Reflect or refract when encountering different materials during propagation.

○ Characteristic 2: Velocity varies based on material through which they pass.

○ Type 1: P-waves

○ Key Features: Primary waves. Speed of 5 ~ 8 km/s. Low amplitude and damage.

○ Passes through solids, liquids, and gases.

○ Wave direction aligns with propagation direction.

○ P-waves drastically decrease at the boundary between the upper mantle and the outer core.

○ Type 2: S-waves

○ Key Features: Shear waves. Speed of about 4 km/s. Greater amplitude and damage.

○ Passes only through solid materials.

○ Wave direction is perpendicular to propagation direction.

○ PS Time (Initial Motion Duration): Time difference between P-waves and S-waves’ arrival.

○ Type 3: L-waves

○ Key Features: Surface waves. Speed of about 3 km/s. High amplitude and destructive. Propagates only on the surface.

○ Both shear and longitudinal waves are present.

○ Category 1: Love Waves

○ Category 2: Rayleigh Waves

○ PS Interval: Measures epicentral or hypocentral distances.

Figure 5. PS Interval and Travel Time Curve

○ Method to determine hypocenter and epicenter through three observatories

○ P: Epicenter

○ Radius of the circle equals hypocentral distance from each observatory

○ Distance between epicenter and hypocenter is half of HH’ length

Figure 6. Method to determine hypocenter and epicenter through three observatories

Figure 7. Enlarged view of observatory A from the above figure

Point O is where the origin (hypocenter) is located, descending vertically by a length of OP or OP’.

○ Time-Distance Curve (Travel-Time Curve) for P-waves describes central P-wave.

Figure 8. P-wave Time-Distance Curve

a represents direct wave, b represents refracted wave, bending point is the cross-over distance

Figure 9. Refracted Wave and Direct Wave

○ Direct Wave: Time taken by direct seismic wave to travel from the epicenter S to observation point D.

○ Refracted Wave: Time taken by seismic wave to reach point D after being refracted at the crust-mantle interface.

○ Reflected Wave: Always arrives later than direct wave.

○ Cross-Over Distance: Distance to the point where direct and refracted waves meet. Proportional to the thickness of the crust.

○ If the hypocentral distance ℓ is short, the shorter distance covered by the direct wave causes it to arrive faster at D.

○ If the hypocentral distance ℓ is long, the difference in travel distances is minimal. Depending on density differences, faster refracted waves arrive at D.

○ Inference 1: Mantle’s P-wave velocity is faster than crustal velocity, as seismic waves refract.

○ Inference 2: Thicker crust results in a longer bending distance in the travel-time curve. With increased distance of the refracted wave, the time taken for it to reach the observation point is delayed.

○ Useful Formulas

④ Estimation Methods for Earth’s Internal Materials

○ Investigate seismic wave velocity distribution in Earth’s interior.

○ High-temperature, high-pressure experiments.

○ Chemical analysis of meteorites.

⑵ Earth’s Layered Structure

① Overview

○ Distinguishable through changes in seismic wave velocities.

○ Pressure and temperature increase with depth.

○ Density: Crust ＜ Mantle ＜ Outer Core ＜ Inner Core

○ Gravitational Acceleration: Highest at mantle’s boundary, decreases towards the center.

Figure 10. Changes in Gravitational Acceleration with Depth

① Crust: Surface to Mohorovičić Discontinuity

○ Mohorovičić Discontinuity (Moho Discontinuity): 0 km to 100 km.

○ Discovered through refraction of nearby travel-time curves.

○ Consists of 1% of Earth’s total volume, solid.

○ Continental Crust: 30 ~ 50 km, average 30 km, density 2.7 g/cm³.

○ Upper Part: Granite rocks (sial layer).

○ Lower Part: Basaltic rocks (sima layer).

○ Oceanic Crust: 6 ~ 8 km, average 6 km, density 3 g/cm³, composed of basaltic rocks (sima layer).

② Mantle: Moho Discontinuity to Gutenberg Discontinuity

○ Structure:

○ Gutenberg Discontinuity: Located at 2,900 km depth. The point where gravity is at its maximum.

○ Mantle = Upper Mantle + Transition Zone + Lower Mantle

○ Upper Mantle (Moho Discontinuity ~ 400 km): Includes the Lithosphere and the Asthenosphere.

○ Transition Zone (400 km ~ 1000 km): In the low-velocity zone, the mantle is ductile, but as the depth increases, it becomes solidified due to pressure. The speed of seismic waves increases because of phase transitions. Magma is most likely to form in this region.

○ Lower Mantle (700 ~ 2,900 km)

○ Plate: A rigid section that includes the crust and the upper mantle.

○ Asthenosphere: Located at a depth of 100 ~ 400 km. Partially molten, leading to a sudden decrease in seismic wave velocity. It serves as the driving force for plate movement.

○ Characteristics:

○ Constitutes about 82% of Earth’s volume, largest volume and mass inside Earth.

○ About 67% of Earth’s total mass.

○ Density: 3.3 g/cm³.

○ Composed mainly of peridotite rocks, ultramafic composition.

○ Seismic Waves:

○ Shadow Zone: Area where seismic waves don’t reach due to presence of the core.

○ P-wave Shadow Zone: Seismic angle of 103 ~ 142°.

○ S-wave Shadow Zone: Seismic angle of 103 ~ 180°.

○ Low-Velocity Layer: Slows seismic waves in the upper mantle.

③ Outer Core: Gutenberg Discontinuity to Lehmann Discontinuity

○ Lehmann Discontinuity (Lehmann Discontinuity): 5,100 km.

○ Liquid state suggested due to presence of S-wave shadow zone.

○ Composed mainly of iron and nickel.

○ Highest rate of pressure increase within the Earth.

④ Inner Core: Lehmann Discontinuity to Earth’s center (6,400 km).

○ Presence of weak P-waves near a seismic angle of 110° suggests its existence.

○ Solid state inferred from increasing P-wave velocity.

○ Mainly composed of iron with some nickel.

⑶ Composition of Earth’s Crustal Materials

① Rocks Composing the Crust

○ The rock-forming minerals that make up the crust are predominantly silicate minerals.

○ Rocks near the surface: Sedimentary rocks (75%), igneous and metamorphic rocks (25%).

○ Rocks at approximately 16 km depth: Sedimentary rocks (5%), igneous and metamorphic rocks (95%).

○ Upper continental crust: Granitic rocks rich in SiO₂ and Al₂O₃ (sial layer), density 2.7 g/㎤.

○ Lower continental crust and oceanic crust: Basaltic rocks rich in SiO₂ and MgO (sima layer), density 3.0 g/㎤.

② Eight Major Elements in the Crust (Mass Fraction)

○ O: 46.6%

○ Si: 27.7%

○ Al: 8.1%

○ Fe: 6.0%

○ Ca: 3.6%

○ Na: 2.8%

○ K: 2.6%

○ Mg: 2.1%

○ Mnemonic Tip: San Gu Al Cheol Na Cheol Ma

③ Clarke Number: Weight percentage of various elements present from sea level to about 16 km below ground.

⑷ Composition of Mantle Materials

① Closer to the crust than the core.

② Composed mainly of peridotite rocks containing pyroxene and olivine.

③ Rich in Fe and Mg, density between 3.3 to 5.5 g/cm³.

⑸ Composition of Core Materials

① Outer Core: Mixture of Fe including Ni (liquid state), density around 11 g/cm³.

② Inner Core: Mixture of Fe including Ni (solid state), density around 16.5 g/cm³.

5. ** **Biosphere

⑴ All living organisms on Earth and organic materials that haven’t decomposed yet.

⑵ Inhabit surface, internal soil, oceans, and subsurface of atmosphere (below about 8 km altitude).

⑶ Plays a crucial role in altering Earth’s atmospheric composition and surface.

Input: 2019.08.16 22:49