Earth Science: Rocks, Minerals, and Earth Systems

Posted on Dec 2, 2024 in Geology

Earth Materials

Rocks and Minerals

Rocks are aggregates of minerals formed by geological processes. A mineral is a naturally occurring element or inorganic compound with a definite chemical composition and atomic structure.

Rock Classification

  • Igneous: Formed from the consolidation of magma.
  • Sedimentary: Formed from the consolidation of sediments.
  • Metamorphic: Formed from other rocks within the Earth’s crust that have undergone transformation.

The Rock Cycle

The rock cycle is the continuous process of transformation between igneous, sedimentary, and metamorphic rocks. Igneous rocks form from the cooling and crystallization of magma. Weathering agents break down these rocks, and the resulting products are transported and deposited as sediments. Lithification transforms sediments into sedimentary rocks. High temperatures and pressures at great depths, along with chemically active gases and solutions, can transform sedimentary rocks into metamorphic rocks. If these rocks melt, they become magma, restarting the cycle.

Igneous Rock Formation

Igneous rocks can be intrusive (formed within the Earth) or extrusive (volcanic rocks formed on the Earth’s surface). Their textures can be described as: holocrystalline, merocrystalline, microcrystalline, vitrophyric, and aphanitic.

Igneous Rock Classification by Silica Content
  • Acidic
  • Neutral
  • Basic
  • Ultrabasic

Sedimentary Rocks

Sedimentary rocks originate from the disintegration of pre-existing rocks. They can be clastic (composed of fragments of other rocks) or non-clastic (chemical or organic). Chemical sedimentary rocks include carbonates, evaporites, siliceous, ferruginous, and phosphatic rocks. Sedimentary rocks exhibit stratification, appearing in distinct layers.

Metamorphic Rocks

Metamorphic rocks are those altered after their formation by changing physicochemical conditions.

Agents of Metamorphism

  • High temperature
  • Fluid pressure
  • Movement of ions

Types of Metamorphism

  • Dynamic: Caused by orogenic pressure.
  • Contact: Due to high temperatures from magma intrusion.
  • Regional: Occurs at depths within geosynclines.

Metamorphic Rock Types

  • Foliated: Exhibit a fissile or slaty structure.
  • Non-foliated: Do not have a fissile structure.

Hydrosphere

The hydrosphere encompasses all water on and below the Earth’s surface.

Ocean Currents

Internal causes of ocean currents include temperature and salinity differences. Tsunamis originate in the deep sea. External causes include drift currents caused by local winds, which are superficial and do not reach significant depths, and wave motions.

Hydrologic Cycle

  1. Solar energy evaporates water from humid areas and plants.
  2. Winds condense water vapor into clouds.
  3. Contact with cold air causes precipitation (rain and snow).
  4. Precipitation contributes to weathering, erosion, transportation, and sedimentation, shaping the landscape; it forms streams and rivers that return water to the sea.
  5. Some rainwater infiltrates the soil, some is used by plants, and the rest returns to the atmosphere.

Water Distribution on Earth

94% of Earth’s water is saline. Most freshwater is underground, with surface freshwater primarily found as ice in polar caps and glaciers, and to a lesser extent, in lakes.

Groundwater

Groundwater exists below the surface, filling cracks, fissures, pores, and cavities in rocks. Aquifers are highly permeable rock layers. Based on depth, aquifers can be classified as:

  • Shallow alluvial: Located a few meters deep, these supplies fluctuate with rainfall and can be easily contaminated.
  • Water table: Accessible by ordinary wells, this aquifer lies above the water table and provides fresh water.
  • Artesian: Confined between two impermeable layers, often in a synclinal structure, this aquifer’s water is under pressure.

Freshwater

Freshwater sources include rivers, streams, creeks, lakes, ponds, and frozen water in glaciers and polar ice caps. Inland waters are crucial for various uses and are integral to the hydrologic cycle, maintaining the balance of ocean salinity.

Atmosphere

The atmosphere is the gaseous layer surrounding Earth, extending approximately 1000 km.

Atmospheric Layers

  • Troposphere: The lowest layer, in contact with the ground, extending up to 16 km at the equator, 14 km in temperate zones, and 10 km in polar regions. Weather changes and atmospheric disturbances originate here.
  • Stratosphere: Located above the troposphere and below the mesosphere, extending from 12.9-19.3 km up to 50 km.
  • Mesosphere: Situated between the stratosphere and the ionosphere, temperatures decrease with altitude, reaching -80°C at 80 miles.
  • Ionosphere: The uppermost layer, characterized by intense solar activity and electrically charged particles (ions and electrons). Ionized by solar radiation, it’s closer to Earth during the day and farther at night.

Weather and Climate

Weather is the focus of meteorology. Climate is the average weather in a specific region over a given period.

Elements of Climate

  • Atmospheric temperature
  • Barometric pressure
  • Atmospheric humidity

Climate Factors

  • Latitude
  • Elevation
  • Relief
  • Planetary winds
  • Ocean currents
  • Land and sea distribution

Soil Formation

After Earth cooled, a rocky mantle formed, from which soil originated through transformations driven by climate variables (humidity, rainfall, temperature), rock type, relief, vegetation, and time.

Stages of Soil Formation

  1. Bedrock Erosion: Exposed bedrock begins weathering.
  2. Degradation: Physical and chemical weathering breaks down rock.
  3. Mineral Soil: Coarse, low-mineralized soil forms.
  4. Plant Colonization: Plants contribute organic matter.
  5. Humification and Mixing: Distinct horizons (A, B, C) develop. Horizon A is rich in organic matter (humus). Horizon B accumulates minerals. Horizon C contains more minerals and bedrock.

Land Modeling

Land modeling is a cyclical process shaping the Earth’s surface.

Processes

  • Decomposition: Water disintegrates rocks.
  • Erosion: Weathered material is transported.
  • Transportation: Sediments are moved by rivers, sea, ice, gravity, or wind.

Types of Land Modeling

  • Fluvial Modeling: Shaped by rivers.
  • Wind Modeling: Shaped by wind erosion.
  • Coastal Modeling: Shaped by tides and waves.

Soil Forms

  • Regolith: The result of rock decomposition.