Study guide
2.3 Earth & Space Science: Geology, Meteorology & Astronomy
Armed Forces Classification Test AFCT
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1 Chapter 1: Guide Scope, AFQT & Service-Specific Policy
1.1 Editorial Scope and Service-Specific AFCT Policy 1.2 AFQT Meaning and Study Priorities 1.3 Service Composites and Targeted Skill Planning 1.4 Format-Agnostic Test Preparation and Pacing
2 Chapter 2: General Science (GS)
2.1 Life Science: Cell Biology, Human Anatomy & Genetics 2.2 Physical Science: Matter, Energy, Forces & Motion 2.3 Earth & Space Science: Geology, Meteorology & Astronomy 2.4 Chemistry Fundamentals: Atomic Structure, Elements & Chemical Reactions
3 Chapter 3: Arithmetic Reasoning (AR)
3.1 Word Problems: Rates, Ratios, Proportions & Percentages 3.2 Financial & Distance Math: Interest, Profit/Loss, Speed & Time 3.3 Work & Mixture Problems: Joint Rates & Percentage Concentrations 3.4 Multi-Step Problem Solving & Algebraic Word Problems
4 Chapter 4: Word Knowledge (WK)
4.1 General Academic & Technical Vocabulary 4.2 Context Clues, Synonyms & Antonyms 4.3 Word Roots, Prefixes & Suffixes (Etymology) 4.4 Advanced Technical & Operational Terminology
5 Chapter 5: Paragraph Comprehension (PC)
5.1 Identifying Main Ideas, Central Themes & Topic Sentences 5.2 Extracting Supporting Details & Factual Information 5.3 Drawing Logical Inferences & Author's Purpose 5.4 Analyzing Text Structure & Drawing Conclusions
6 Chapter 6: Mathematics Knowledge (MK)
6.1 Pre-Algebra & Number Operations: Exponents, Radicals & Order of Operations 6.2 High School Algebra: Linear Equations, Inequalities & Polynomials 6.3 Geometry Fundamentals: Angles, Triangles, Quadrilaterals & Circles 6.4 Coordinate Geometry, Perimeter, Area & Volume Formulas
7 Chapter 7: Electronics Information (EI)
7.1 Electrical Principles: Voltage, Current, Resistance & Ohm's Law (V=IR, P=VI) 7.2 Electric Circuits: Series, Parallel & Combination Circuit Analysis 7.3 Electrical Components: Resistors, Capacitors, Inductors & Transformers 7.4 Electronic Semiconductors, Transistors, Diodes & Logic Gates
8 Chapter 8: Auto & Shop Information (AS)
8.1 Automotive Systems: Internal Combustion Engines, Fuel & Ignition Systems 8.2 Automotive Mechanical Systems: Transmission, Suspension, Brakes & Cooling 8.3 Hand & Power Tools: Identification, Uses & Fasteners 8.4 Shop Practice, Woodworking, Metalworking & Safety Rules
9 Chapter 9: Mechanical Comprehension (MC)
9.1 Simple Machines: Levers, Pulleys, Inclined Planes & Mechanical Advantage 9.2 Force, Motion, Work & Power: Newton's Laws & Energy Transformations 9.3 Fluid Dynamics & Pressure: Pascal's Principle, Hydraulics & Pneumatics 9.4 Mechanical Components: Gears, Belts, Springs & Friction
10 Chapter 10: Spatial Assembly Practice (AO Skill)
10.1 Spatial Connections and Assembly Patterns
2.3 Earth & Space Science: Geology, Meteorology & Astronomy
Key Takeaways Explain This Topic AI
Earth's interior comprises four main layers: solid inner core, liquid outer core (generates magnetic field), mantle (asthenosphere), and solid crust (lithosphere).
Plate tectonics drives continental drift, volcanism, and seismic activity across convergent (colliding), divergent (separating), and transform (sliding) plate boundaries.
The rock cycle continuously transforms rocks among Igneous (cooled lava/magma), Sedimentary (compacted sediments), and Metamorphic (heat and pressure altered) forms.
Earth's atmosphere consists of 78% Nitrogen and 21% Oxygen, divided into five thermal layers: Troposphere (weather layer), Stratosphere (ozone layer), Mesosphere, Thermosphere, and Exosphere.
The solar system consists of 8 major planets orbiting the Sun, categorized into 4 inner rocky terrestrial planets and 4 outer gas/ice giant planets.
Last updated: July 2026
Earth & Space Science: Geology, Meteorology & Astronomy
Earth and Space Science encompasses geology (the study of Earth's solid structure and history), meteorology (atmospheric science and weather), oceanography, and astronomy (the study of the universe beyond Earth).
1. Earth's Interior Structure & Plate Tectonics
Earth is an oblate spheroid with a layered interior structure categorized by chemical composition and mechanical properties:
Internal Layers of the Earth
Layer Thickness / Depth State of Matter & Composition
Crust 5 – 70 km 5\text{--}70\text{ km} 5 – 70 km Solid outer rock shell; Oceanic Crust (thin, dense basalt) and Continental Crust (thick, less dense granite).
Mantle ∼ 2 , 900 km \sim 2,900\text{ km} ∼ 2 , 900 km Semifluid silicate rock. Upper mantle contains the ductile Asthenosphere on which tectonic plates float.
Outer Core ∼ 2 , 200 km \sim 2,200\text{ km} ∼ 2 , 200 km Liquid iron and nickel . Convection currents in the outer core generate Earth's geomagnetic field .
Inner Core ∼ 1 , 220 km \sim 1,220\text{ km} ∼ 1 , 220 km radius Solid iron and nickel ball . Remains solid despite intense heat ( > 5 , 000 ∘ C > 5,000^\circ\text{C} > 5 , 00 0 ∘ C ) due to immense pressure.
Plate Tectonics
Earth's rigid outer shell, the lithosphere , is broken into major and minor tectonic plates that drift across the underlying asthenosphere driven by mantle convection currents.
Divergent Boundaries : Plates pull apart from each other. Magma rises to create new oceanic crust (e.g., Mid-Atlantic Ridge, East African Rift).
Convergent Boundaries : Plates collide. Subduction occurs when dense oceanic crust sinks beneath continental crust (forming ocean trenches and volcanic arcs, e.g., the Andes). Collision of two continental plates pushes up mountain ranges (e.g., the Himalayas).
Transform Boundaries : Plates slide horizontally past one another along strike-slip faults, creating intense earthquakes without creating or destroying crust (e.g., San Andreas Fault).
2. Geology: The Rock Cycle & Weathering
Rocks are naturally occurring solid aggregates of minerals. The Rock Cycle describes how rocks constantly transform between three fundamental types: [Cooling & Crystallization]
- +-------------------------------------------------+
- | |
- v |
- IGNEOUS ROCK ----(Weathering/Erosion)----> SEDIMENTS |
- | | |
- (Heat & (Lithification/|
- Pressure) Compaction) |
- | | |
- v v |
- METAMORPHIC ROCK <--(Heat & Pressure)-- SEDIMENTARY ROCK|
- | |
- +---------------> [Melting Magma] ----------------+
- The Three Main Rock Classes
Igneous Rocks : Formed from the cooling and solidification of molten rock.
Intrusive (Plutonic) : Cooled slowly beneath Earth's surface; large visible crystals (e.g., Granite ).
Extrusive (Volcanic) : Cooled rapidly on Earth's surface after eruption; small or microscopic crystals (e.g., Basalt , Obsidian , Pumice ).
Sedimentary Rocks : Formed over time through the weathering of existing rocks, transport of sediment, deposition, compaction, and cementation ( lithification ). Often contain fossils (e.g., Sandstone , Limestone , Shale ).
Metamorphic Rocks : Formed when existing rocks are subjected to high heat and extreme pressure deep underground without melting, altering their mineral structure (e.g., Limestone becomes Marble , Shale becomes Slate ).
3. Meteorology & Earth's Atmosphere
Earth's atmosphere is composed primarily of Nitrogen ( 78 % 78\% 78% ) , Oxygen ( 21 % 21\% 21% ) , Argon ( 0.9 % 0.9\% 0.9% ) , and trace gases including Carbon Dioxide ( 0.04 % 0.04\% 0.04% ) and water vapor.
Layers of the Atmosphere
Layer Altitude Range Distinctive Characteristics
Troposphere 0 to 12 km 0 \text{ to } 12\text{ km} 0 to 12 km Lowest layer containing 75 % 75\% 75% of atmospheric mass; all weather occurs here ; temperature drops with altitude.
Stratosphere 12 to 50 km 12 \text{ to } 50\text{ km} 12 to 50 km Contains the Ozone Layer ( O 3 O_3 O 3 ) which absorbs harmful solar UV radiation; temperature increases with altitude.
Mesosphere 50 to 85 km 50 \text{ to } 85\text{ km} 50 to 85 km Coldest layer of the atmosphere (down to − 90 ∘ C -90^\circ\text{C} − 9 0 ∘ C ); meteors burn up here due to atmospheric friction.
Thermosphere 85 to 600 km 85 \text{ to } 600\text{ km} 85 to 600 km Extremely high temperatures; contains the Ionosphere (charged ions) which reflects radio waves and produces auroras.
Exosphere > 600 km > 600\text{ km} > 600 km Outermost fringe transitioning into outer space; satellites orbit in this region.
Weather Systems & Fronts
Air Pressure : Measured with a barometer . High-pressure systems ( H H H ) bring clear, dry weather; Low-pressure systems ( L L L ) bring clouds, precipitation, and storms.
Cold Front : A cold air mass advances and wedges beneath warm air, causing rapid lift and intense thunderstorms followed by cooler, clear weather.
Warm Front : Warm air gradually slides over a retreating cold air mass, producing widespread light-to-moderate rain and cloudiness.
Coriolis Effect : Deflection of air currents caused by Earth's rotation (deflects winds to the right in the Northern Hemisphere and left in the Southern Hemisphere).
4. Oceanography & The Water Cycle
Water moves continuously between Earth's surface reservoirs via the Hydrological (Water) Cycle :
Evaporation : Liquid water converted to water vapor by solar heat.
Transpiration : Water vapor released by plants through leaf stomata.
Condensation : Water vapor cools and condenses into cloud droplets.
Precipitation : Water falls to Earth as rain, snow, sleet, or hail.
Runoff & Infiltration : Water flows into surface streams or seeps into soil to replenish groundwater aquifers.
Oceans : Cover ∼ 71 % \sim 71\% ∼ 71% of Earth's surface and hold 97 % 97\% 97% of total global water. Average ocean salinity is approximately 35 parts per thousand (ppt) 35\text{ parts per thousand (ppt)} 35 parts per thousand (ppt) ( 3.5 % 3.5\% 3.5% salt concentration, primarily N a C l NaCl N a Cl ).
5. Astronomy: Solar System & The Universe
Planetary Order from the Sun Sun → Mercury → Venus → Earth → Mars → [ A s t e r o i d B e l t ] → Jupiter → Saturn → Uranus → Neptune \text{Sun} \rightarrow \text{Mercury} \rightarrow \text{Venus} \rightarrow \text{Earth} \rightarrow \text{Mars} \rightarrow \mathbf{[Asteroid\,Belt]} \rightarrow \text{Jupiter} \rightarrow \text{Saturn} \rightarrow \text{Uranus} \rightarrow \text{Neptune} Sun → Mercury → Venus → Earth → Mars → [ Asteroid Belt ] → Jupiter → Saturn → Uranus → Neptune
Terrestrial Planets (Mercury, Venus, Earth, Mars): Small, dense, rocky compositions with solid surfaces.
Gas Giants / Ice Giants (Jupiter, Saturn, Uranus, Neptune): Large, low-density planets composed primarily of hydrogen, helium, water, ammonia, and methane ice.
Astronomical Unit (AU) : The average distance from Earth to the Sun, approximately 150 million km 150 \text{ million km} 150 million km ( 93 million miles 93\text{ million miles} 93 million miles ).
Earth-Moon-Sun Interactions & Tides
Lunar Phases : Caused by the changing relative positions of Earth, Moon, and Sun over a 29.5-day cycle.
Solar Eclipse : Occurs when the Moon passes directly between Earth and Sun ( New Moon phase), casting a shadow on Earth.
Lunar Eclipse : Occurs when Earth passes directly between Sun and Moon ( Full Moon phase), blocking sunlight from illuminating the Moon.
Ocean Tides : Gravitational pull of the Moon and Sun creates ocean bulges. Spring Tides (highest high tides) occur during New and Full Moons when Sun, Moon, and Earth align. Neap Tides (lowest tide variation) occur during 1st and 3rd Quarter Moons when gravitational pulls act at right angles.