College of UAEU Science GEOLOGY DEPARTMENT

Course: Physical Geology (GEOL 100)

University: United Arab Emirates University

Chapter 1: Introduction to Earth

Main Topics Covered

• Geology & Physical Geology

• Origin of Earth

• Earth as a System

• Earth’s Internal Structure

• Dynamic Layers

• Geologic Time

Geology & Physical Geology

Definition of Geology: The study of Earth (Geo = Earth, logy = Science).Definition of Physical Geology: Science that studies Earth’s materials and processes above and beneath the surface.

Origin of Earth

Earth is one of eight major planets orbiting the Sun, formed from a vast nebula of dust and gases, as suggested by the nebular hypothesis. Formation Process:

• Approximately 5 billion years ago, the nebula contracted, leading to rotation and flattening into a disk.

• Nuclei formed smaller accumulations, culminating in planet formation, with the Sun at the center.

• The atmosphere formed from volcanic gases, and oceans developed through cooling and condensation.

Earth's Spheres

• Hydrosphere: 71% water covering Earth’s surface; crucial for life and landforms.

• Biosphere: All life forms on land and sea.

• Atmosphere: Five layers (Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere); primarily Nitrogen (78%) and Oxygen (21%).

• Lithosphere (Geosphere): Rigid outer layer (crust) and upper mantle, underlain by plastic asthenosphere.

Earth Materials

• Organic Compounds: Carbon-based substances like wood and oil.

• Minerals: Inorganic crystals that form most Earth rocks, mainly silicates.

• Rocks: Composed of minerals, categorized as:

  • Igneous: Formed from liquid rock.

  • Sedimentary: Formed from cemented debris.

  • Metamorphic: Changed by heat and pressure.

• Metals & Volatiles: Metallic elements and materials that vaporize at the surface, released during volcanism.

Earth’s Internal Structure

Earth has layers: Crust, Mantle (lithosphere and asthenosphere), and Core (outer liquid and inner solid). Seismic waves help us understand this structure.

Mechanical Layers

• Lithosphere: A rigid shell averaging 100 km thick, composed of crust and upper mantle.

• Asthenosphere: Beneath the lithosphere, consisting of soft, weak rocks.

Dynamic Earth

Earth experiences destructive processes (weathering, erosion) and constructive processes (volcanism, mountain building).

Age of the Earth

Earth is approximately 4.6 billion years old. Relative Age Determination uses principles like:

• Law of Superposition: Older layers are beneath younger ones in sedimentary strata.

• Principle of Faunal Succession: Fossils occur in a specific sequence to correlate rock layers.

Absolute Age Determination: The discovery of radioactive materials has helped establish timelines for Earth’s events.

Geologic Time Scale:

• Phanerozoic Eon: Abundant life lasting about 600 million years; divided into Paleozoic, Mesozoic, and Cenozoic eras.

• Precambrian Eon: Extends before the Phanerozoic, with limited life presence.

Historical Notes about Geology

• Catastrophism: Earth’s landforms resulted from sudden, catastrophic events.

• Uniformitarianism: Geological processes today also occurred in the past, establishing a long geological history and gradual change. Coined by James Hutton in the late 1700s.

End of Chapter 1

Next: Chapter 2: Plate Tectonics