Earth Science Reviewer

🌐 Earth System

The Earth is made of interconnected subsystems that work together to make our planet habitable.

•Atmosphere – the gaseous layer surrounding Earth.

Made of nitrogen, oxygen, carbon dioxide, and other gases.

-Functions:

Shields Earth from harmful solar radiation.

Regulates temperature (greenhouse effect).

Provides gases essential for life (oxygen for breathing, CO₂ for plants).

•Hydrosphere – all water on Earth (oceans, rivers, lakes, groundwater, glaciers, and even water vapor in the atmosphere).

-Connected system of water circulation.

-Important for weather, climate, and sustaining life.

•Geosphere – the solid Earth (rocks, mountains, soil, crust, mantle, core).

-Source of minerals, energy, and land where humans live.

•Biosphere – all living things on Earth.

-Depends on air, water, and land from other systems.

🌎 Layers of the Earth

•Crust – thin, outermost solid shell.

-Continental crust (land, thicker, less dense).

-Oceanic crust (under oceans, thinner, denser).

•Mantle – thick, semi-solid layer beneath crust.

-Lithosphere = crust + upper mantle (rigid).

•Outer Core – liquid iron and nickel.

-Movement of liquid metals generates Earth’s magnetic field.

•Inner Core – solid iron and nickel (extremely hot, but solid due to high pressure).

Rocks

•Rocks are aggregates of minerals. They are classified based on how they are formed.

•Igneous Rocks (formed from cooling magma/lava)

•Extrusive (Volcanic) – formed outside Earth’s surface, cools quickly → fine-grained, small crystals (e.g., basalt).

•Intrusive (Plutonic) – formed inside Earth, cools slowly → large crystals (e.g., granite).

•Sedimentary Rocks (formed from sediments)

-Process: Weathering → Erosion → Deposition → Compaction → Cementation.

•Clastic – made of fragments of other rocks (e.g., sandstone).

•Non-clastic – formed from evaporation or chemical processes (e.g., limestone, rock salt).

•Metamorphic Rocks (changed by heat and pressure)

•Regional Metamorphism – formed by pressure over large areas (mountain formation).

•Contact Metamorphism – formed by heat when magma touches rocks.

•Foliated – layered appearance (e.g., slate, schist).

√Non-foliated – no layers, uniform texture (e.g., marble).

Minerals

•Minerals = naturally occurring, inorganic substances with definite chemical composition and crystalline structure.

•Properties of Minerals

—Luster – how light reflects from surface.

-Metallic (shiny, like metals).

-Non-metallic (dull, glassy, earthy).

—Hardness – resistance to scratching.

-Measured using Mohs Hardness Scale (1–10).

-Example: Talc (1) = softest, Diamond (10) = hardest.

•Color & Streak

—Color – can vary due to impurities (not always reliable).

—Streak – color of powdered mineral (more reliable).

—Crystal Form/Habit – external shape of crystals (cubic, hexagonal, etc.).

—Breakage

-Cleavage – breaks along flat planes.

-Fracture – breaks irregularly (rough or jagged).

—Specific Gravity – density of the mineral (heaviness compared to water).

• Importance of Minerals

—Construction – cement, steel, glass.

—Transportation – cars, ships, planes use mineral-based materials.

—Electronics – silicon (computers), copper (wires), lithium (batteries).

—Medicine – calcium, iodine, iron are essential for health.

—Agriculture – fertilizers (phosphate, potassium, nitrogen).

•Without minerals → industries, technology, and daily life would collapse.

🌐

Earth System The Earth is made of interconnected subsystems that work together to make our planet habitable.

Atmosphere – the gaseous layer surrounding Earth, extending up to hundreds of kilometers. It is primarily made of nitrogen ( $N<em>2$ , approx. $78\%%$ ), oxygen ( $O</em>2$ , approx. $21\%%$ ), argon ( $Ar$ , approx. $0.9\%%$ ), carbon dioxide ( $CO_2$ , approx. $0.04\%%$ ), and trace amounts of other gases and water vapor.
- Functions: Shields Earth from harmful solar radiation (e.g., UV radiation absorbed by the ozone layer). Regulates temperature through the greenhouse effect, trapping heat and preventing extreme temperature fluctuations. Provides gases essential for life (oxygen for respiration, carbon dioxide for photosynthesis in plants). Drives weather and climate patterns through atmospheric circulation.
Hydrosphere – encompasses all water on Earth, in all its forms: oceans, seas, rivers, lakes, groundwater, glaciers, ice caps, and even water vapor and clouds in the atmosphere.
- Connected System: It is a dynamic system of water circulation, constantly moving through the water cycle (evaporation, condensation, precipitation, runoff, infiltration). Its enormous heat capacity helps regulate global temperatures and climate.
- Importance: Crucial for weather, climate regulation, nutrient cycling, and sustaining all known forms of life. Oceans cover approximately $71\%%$ of Earth's surface.
Geosphere – the solid Earth, including rocks, minerals, mountains, landforms, soil, and all the layers from the surface (crust) down to the core.
- Dynamic Processes: Involved in processes like plate tectonics, seismic activity (earthquakes), volcanism, and the rock cycle. It is the source of vital minerals, fossil fuels, and the land surface where terrestrial life exists.
Biosphere – integrates all living things on Earth, from the deepest ocean trenches to the highest mountains, including plants, animals, microorganisms, and humans.
- Interdependence: It is deeply intertwined with and dependent on the air (atmosphere), water (hydrosphere), and land (geosphere) for resources and habitats. Living organisms significantly modify the Earth's other systems through processes like photosynthesis, respiration, and decomposition.

🌎

Layers of the Earth The Earth is composed of distinct concentric layers, each with unique characteristics.

Crust – the thin, outermost solid shell of the Earth, varying in thickness from about $5$ km to $70$ km.
- Continental Crust: Thicker ( $25$ – $70$ km), less dense ( $2.7$ $g/cm^3$ ), primarily composed of granitic and felsic rocks (rich in silica and aluminum).
- Oceanic Crust: Thinner ( $5$ – $10$ km), denser ( $3.0$ $g/cm^3$ ), primarily composed of basaltic and mafic rocks (rich in iron and magnesium).
Mantle – a thick, semi-solid, viscous layer beneath the crust, extending to a depth of about $2,900$ km. It makes up about $84\%%$ of Earth's volume.
- Composition: Predominantly composed of silicate rocks rich in iron and magnesium. Temperatures range from about $500$ ${^\circ}C$ at the top to over $4,000$ ${^\circ}C$ near the core.
- Lithosphere: Consists of the crust and the rigid uppermost part of the mantle. It is divided into tectonic plates that move over the asthenosphere.
- Asthenosphere: A weaker, ductile layer within the upper mantle directly below the lithosphere, where convection currents occur, driving plate tectonics.
Outer Core – a liquid layer composed mainly of molten iron and nickel, extending from $2,890$ km to $5,150$ km deep.
- Magnetic Field: Convective motion of these electrically conductive liquid metals generates Earth’s powerful magnetic field, which protects the planet from harmful solar winds and cosmic rays.
Inner Core – the Earth's innermost layer, a solid sphere composed primarily of iron and nickel, with a radius of about $1,220$ km.
- Conditions: Despite extreme temperatures (estimated $5,200$ ${^\circ}C$ , similar to the sun's surface), it remains solid due to immense pressure from the overlying layers (over $3.6$ million atmospheres).

Rocks Rocks are naturally occurring solid aggregates of one or more minerals or mineraloids. They are classified based on their origin and the geological processes by which they are formed.

Igneous Rocks (formed from cooling and solidification of molten rock, magma or lava)
- Extrusive (Volcanic) – formed when lava cools quickly at or near Earth’s surface (e.g., from volcanic eruptions). Rapid cooling prevents large crystal growth, resulting in fine-grained or glassy textures (e.g., basalt, obsidian, pumice).
- Intrusive (Plutonic) – formed when magma cools slowly beneath Earth’s surface. Slow cooling allows for the growth of larger, visible interlocking crystals, resulting in a coarse-grained texture (e.g., granite, gabbro, diorite).
Sedimentary Rocks (formed from the accumulation, compaction, and cementation of sediments)
- Process: Involves weathering (breaking down existing rocks), erosion (transportation of weathered material), deposition (settling of sediments), compaction (reduction of pore space due to pressure), and cementation (minerals crystallizing in pores, binding grains together).
- Clastic: Made of fragments (clasts) of pre-existing rocks, minerals, or organic matter. Classified by grain size (e.g., conglomerate (large), sandstone (sand-sized), shale (clay-sized)).
- Chemical/Non-clastic: Formed from the precipitation of minerals from water (e.g., limestone from calcium carbonate, rock salt from halite, chert). Can also include biogenic rocks formed from organic remains (e.g., coal, chalk).
Metamorphic Rocks (formed when pre-existing rocks are transformed by intense heat, pressure, and/or chemically active fluids without melting)
- Regional Metamorphism: Occurs over large areas, typically during mountain-building events (orogenesis) due to tectonic plate collisions, involving high pressure and moderate to high temperatures. Results in foliated textures (e.g., slate, schist, gneiss).
- Contact Metamorphism: Occurs when rocks are heated by contact with a hot intrusion of magma or lava. Characterized by high temperatures and relatively low pressures, often resulting in non-foliated textures (e.g., marble from limestone, quartzite from sandstone).
- Foliated: Rocks display a layered or banded appearance due to the alignment of mineral grains under differential pressure (e.g., slate, phyllite, schist, gneiss - increasing metamorphic grade).
- Non-foliated: Rocks do not show a layered texture, often formed under uniform pressure or composed of minerals that do not readily align (e.g., marble, quartzite, hornfels).

Minerals Minerals are naturally occurring, inorganic solid substances with a definite chemical composition and a characteristic orderly crystalline (atomic) structure.

Properties of Minerals —Each property is a result of its unique chemical composition and internal atomic arrangement.
- Luster – describes how light reflects from the surface of a mineral, giving it a characteristic sheen.
  - Metallic: Shiny, opaque, like polished metal (e.g., galena, pyrite).
  - Non-metallic: Can be vitreous (glassy, e.g., quartz), pearly (e.g., talc), silky (e.g., asbestos), resinous (e.g., sphalerite), earthy (dull, e.g., kaolinite), or dull.
- Hardness – a mineral's resistance to scratching or abrasion. It reflects the strength of the chemical bonds within the mineral's structure.
  - Measured using Mohs Hardness Scale, a relative scale from $1$ (softest) to $10$ (hardest).
  - Example: Talc ( $1$ ) is the softest, easily scratched by a fingernail. Diamond ( $10$ ) is the hardest known natural mineral.
- Color & Streak
  - Color: The appearance of the mineral in reflected light. Can be highly variable and unreliable for identification due to impurities or mineral alteration (e.g., quartz can be clear, white, pink, purple).
  - Streak: The color of a mineral's powder when rubbed across an unglazed porcelain plate. It is a more reliable diagnostic property as it is less affected by impurities (e.g., hematite can be black or red, but always has a reddish-brown streak).
- Crystal Form/Habit – the external shape a mineral's crystals naturally grow into under ideal conditions, reflecting its internal atomic structure (e.g., cubic (halite), hexagonal (quartz), tabular, prismatic, acicular).
- Breakage
  - Cleavage: The tendency of a mineral to break smoothly along specific, flat planes of weakness in its atomic structure (e.g., mica has perfect one-directional cleavage, halite has cubic cleavage).
  - Fracture: The irregular or uneven way a mineral breaks when it does not cleave. Can be conchoidal (shell-like, e.g., quartz), fibrous, hackly (jagged, e.g., copper), or earthy.
- Specific Gravity – the ratio of the density of a mineral to the density of water (at $4$ ${^\circ}C$ ). It is a measure of how heavy the mineral is for its size (e.g., galena has a high specific gravity, while quartz has a relatively low one).
Importance of Minerals —Minerals are fundamental to all aspects of modern society and natural processes.
- Construction: Essential components in building materials (e.g., gypsum for plaster, limestone for cement, iron ore for steel, silica sand for glass).
- Transportation: Vehicles, ships, and planes rely on metals (e.g., aluminum, iron, titanium) derived from minerals for structural integrity and functionality.
- Electronics: Critical for modern technology (e.g., silicon for semiconductors, copper for wires, lithium for batteries, rare earth elements for displays and magnets).
- Medicine: Many minerals or their derived elements are crucial for human health (e.g., calcium for bones, iodine for thyroid function, iron for blood, zinc for immunity).
- Agriculture: Key ingredients in fertilizers (e.g., phosphate minerals, potash/potassium minerals, nitrogen-containing compounds) to enrich soil and support crop growth.
- Without minerals → industries, technology, infrastructure, medicine, and daily life would not be possible and would effectively collapse. Minerals are non-renewable resources, emphasizing the need for sustainable use and recycling.