Earth Science Notes: Earth's Systems, Minerals, and Rocks

Earth and the Earth's System

Earth Subsystems

  • The Earth is the third planet from the sun and is unique in supporting life.
  • The Earth system consists of interacting physical, chemical, and biological processes.
  • The Earth system includes all matter (living and non-living), energy, and processes within Earth's boundary.
  • The Earth system is powered by the sun and the planet’s internal heat.
  • The Earth is approximately 4,600,000,000 years old.
  • The Earth's parts (land, water, air, and life) are interconnected and continuously interact.
  • These interacting parts are called subsystems:
    • Lithosphere (or Geosphere)
      • The solid Earth, from the Greek word lithos meaning "stone."
      • Includes the crust and the solid uppermost mantle.
      • The asthenosphere is the lower soft layer after the lithosphere.
      • The lithosphere is divided into huge plates that move according to the plate tectonic theory.
    • Atmosphere
      • The gaseous Earth.
      • A mixture of gases surrounding the Earth, providing air to breathe and shielding from harmful UV radiation.
      • Five Layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
      • Temperature decreases in the troposphere, increases in the stratosphere, decreases in the mesosphere, and increases in the thermosphere.
      • The mesosphere is the coldest layer, and the thermosphere is the hottest.
      • The Earth's atmosphere is composed of approximately 78\% nitrogen, 21\% oxygen, 0.9\% argon, and 0.1\% other gases.
      • The early Earth's atmosphere had lots of water vapor but no oxygen.
        • Radiation from the sun caused water to split into oxygen and hydrogen.
        • Cyanobacteria evolved and began carrying out photosynthesis, becoming the main source of oxygen.
    • Hydrosphere
      • The liquid Earth.
      • The total amount of water on a planet, including water on the surface, underground, and in the air.
      • In Earth's early history (Hadean era), volcanic eruptions spewed gases like water vapor, carbon dioxide, carbon monoxide, sulfur dioxide, and other gases.
      • As Earth cooled, water vapor condensed to form the early ocean.
      • Oceans and seas:
        • A sea is a part of an ocean that is partially surrounding a landform (island sea).
        • An ocean is a body of saltwater with almost no boundaries and limitless volume.
      • Saltwater accounts for 97.5\% of the water on Earth's crust, while only 2.5\% is fresh water, with only 30\% of the freshwater being accessible (the rest is locked up in glaciers).
      • Oceans are divided into zones:
        • Intertidal zone: the region exposed during low tide and covered during high tide.
        • Neritic zone: lies above the continental shelf.
        • Oceanic zone: extends from the edge of the continental shelf over the ocean floor and is characterized by darkness.
    • Biosphere
      • The living Earth.
      • Contains the entirety of Earth's living things.
      • The global ecological system integrating all living things and their interactions with the lithosphere, hydrosphere, and atmosphere.
      • Living things form ecological communities (biomes) based on the physical surroundings of an area.

Minerals

  • Geology studies the solid matter that makes up the Earth, changes of the earth over time, it's physical structure and substance.
  • Mineralogy defines a mineral as a solid chemical compound with a well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.
  • Requirements for a matter to be considered a mineral:
    1. Naturally Occurring: Formed by natural processes, not man-made or created in a laboratory.
    2. Chemically Inorganic: Not involving organic life or products created by organic life.
    3. Homogeneous Solids: Chemically and physically uniform down to the atomic level, resulting in predictable physical properties.
    4. Definite Chemical Composition: Always contains certain elements in the same proportion.
    5. Ordered Internal Structure: Atoms arranged in a systematic and repeating pattern.
  • Minerals are distinguished based on physical and chemical properties using laboratory and field techniques.

Physical Properties of Minerals

  • Color: Can be used to easily identify a mineral but is not always reliable, as some minerals can occur in various colors due to impurities or other factors.
  • Hardness: The mineral’s resistance to scratching measured using the Mohs Scale developed by Frederick Mohs. The harder the mineral, the greater is its resistance to scratching.
    • Mohs Scale: Ranges from 1 (softest) to 10 (hardest).
    • Field Hardness Scale: Involves rubbing the mineral against fingers or other tools.
  • Crystalline structure: Tells how a mineral’s crystals are arranged.
    • Crystal solid: Forms a regular repeating three-dimensional crystal lattice
    • Amorphous solid: Forms aggregate that have no particular order or arrangement
  • Streak: The color of the mineral in its powdered form, a more reliable property than color.
  • Cleavage and Fracture: Diagnostic features of many minerals.
    • Cleavage: Mineral breaks along a specific plane or planes.
    • Fracture: Irregular break.
  • Transparency (Diaphaneity): Indicates the extent of light that can pass through the mineral, depending on its thickness.
  • Magnetism: The ability of a mineral to attract or repel other minerals.
  • Tenacity: The level of resistance or reaction of minerals to stress (crushing, bending, breaking, tearing), indicating if a mineral is brittle, malleable, elastic, etc.
  • Luster: The reaction of a mineral to light, determining how brilliant or dull the mineral is.
  • Odor: A distinct smell of a mineral released from a chemical reaction when subjected to water, heat, air, or friction.
  • Specific Gravity: A measure of the density of a mineral, comparing its weight to that of water.

Chemical Properties of Minerals

  • Minerals are classified according to their chemical composition.
    1. Silicates: Most minerals in the earth’s crust and mantle are silicate minerals. All silicate minerals are built of silicon-oxygen tetrahedra in different bonding arrangements which create different crystal lattices. Understanding the crystal lattice helps determine properties like crystal shape and cleavage.
    2. Carbonates: Minerals based on the carbonate ion. They tend to dissolve relatively easily in water, especially acid water.
    3. Sulfates: Minerals usually formed in high evaporation areas with salty water.
    4. Halides: These have a halogen element as the anion (fluoride, chloride, bromide, iodide, or astatine). Usually form in lakes, ponds, and other landlocked seas.
    5. Oxides: Based on the oxygen anion. Form as precipitates close to Earth’s surface or as oxidation products of minerals during weathering.
    6. Sulfides: Contain important metals like copper, lead, and silver. Found in electrical wiring, industrial materials, etc.
    7. Phosphates: Have the polyatomic phosphate ion. Fluorapatite, which makes your teeth hard, is a phosphate mineral.
    8. Native Elements: Made of a single element. Examples include gold (Au), native copper (Cu), and diamond and graphite (carbon).
  • An ore is a rock that contains minerals with useful elements.
    • The cost of creating a product from a mineral depends on its abundance and the extraction/refining costs.
    • Mineral resources should be used wisely.
    • A mineral deposit is only mined if it is profitable (ore deposit).
      • Surface mining extracts ores close to Earth’s surface.
      • Underground mining recovers ores deeper into Earth’s surface.

Rocks

  • Rocks are any naturally occurring solid mass or aggregate of minerals, categorized by the minerals included, chemical composition, and formation.
  • Three basic types of rocks:
    • Igneous Rocks: Crystallized rocks solidified from magma (from the Latin word ignis meaning "fire").
      • Magma rises from the asthenosphere or base of the crust through volcanoes or cracks on Earth's surface.
      • Lava is molten volcanic material on the surface of Earth.
      • Categories:
        • Extrusive: Formed on the surface of the Earth from lava.
        • Intrusive: Formed from magma that cools and solidifies within the crust of the planet.
    • Sedimentary Rocks: Formed from the deposition of different materials on Earth's surface (from the root word sediments which means "remaining particles").
      • Come from preexisting rocks or pieces of dead organisms lithified or cemented together by natural processes.
      • Usually show distinct layering or bedding on the surface.
    • Metamorphic Rocks: Derived from igneous or sedimentary rocks exposed to high pressure, high temperature, or a combination of both, deep below the surface of Earth (meta means "change" and morph means "form").
      • Some minerals undergo chemical and physical changes.

Rock Cycle

  • Rocks of any type can be converted into any other type, or into another rock of the same type.
  • Igneous rock can change into sedimentary rock or into metamorphic rock.
  • Sedimentary rock can change into metamorphic rock or into igneous rock.
  • Metamorphic rock can change into igneous or sedimentary rock.
  • Igneous rocks form when molten magma cools and crystallizes on the Earth's surface or deep within its crust.
  • Over time, weathering breaks down these rocks, mixing them with other materials and transporting them.
  • Compaction and cementation turn this mixture into sedimentary rocks.
  • With exposure to heat and pressure, rocks change physically and chemically, leading to the creation of metamorphic rocks.
  • Sometimes, sedimentary and metamorphic rocks get pushed deep underground and transform back into igneous rocks through subduction into the mantle.