Geologic Processes and the Geologic Time Scale

Alfred Wegener's Theory: Alfred Wegener theorized that all of Earth's continents were once combined into a single supercontinent called Pangaea. However, Wegener was unable to explain the mechanism driving why these continents moved away from one another.
Emergence of Plate Tectonics: Several years after Wegener's proposal, the theory of plate tectonics emerged based on his original concept, providing the explanation for how and why tectonic plates move.
Global Geography and Continents:
- Earth's surface is divided into seven continents: Asia, Europe, Australia, Africa, Antarctica, North America, and South America.
- The Philippines belongs to Asia, which is the largest and most diverse among all continents.
Pangaea and Panthalassa:
- In ancient geologic history, the supercontinent Pangaea was surrounded by a single vast ocean named Panthalassa.
- Pangaea was comprised of several tectonic plates.
- Over time, magma from underneath the surface of Earth began to rise up, eventually causing the supercontinent to break up and separate into distinct landmasses.

Structure of Earth over time

Definition of Plate Boundary: A plate boundary is the area or region where tectonic plates hit each other or move away from each other.
Mechanism of Seismic Activity:
- When tectonic plates interact at boundaries, pressure builds up over time.
- The sudden slipping of these tectonic plates releases energy in the form of seismic waves, causing the shaking of Earth's crust.
Types of Plate Movements: Plate tectonic movements are classified into three primary types:
- Divergent movement
- Convergent movement
- Transform movement
Divergent Plate Boundary Dynamics:
- Definition: Divergent boundaries (also known as divergent plate boundaries) occur when tectonic plates move away from each other.
- Convection Currents: Divergent movements are driven by convection currents that push tectonic plates upward and cause them to break. As the convection current flows laterally beneath the surface, this lateral flow carries the blocks or plates along with it.
- Subtypes of Divergent Boundaries:
- Continental Divergent Boundary: Occurs underneath continental plates. The underlying convection current lifts blocks of tectonic plates and creates a fracture or rift on Earth's surface. As the plates separate and fractures develop, earthquakes are expected to occur.
- Oceanic Divergent Boundary: Occurs underneath oceanic plates.

Dynamic Nature of Earth: Earth undergoes continuous geologic processes that transform physical structures, alter global climate, develop ecosystems, and influence the evolution of living organisms.
Key Geologic Processes:
1. Erosion: The geologic process in which rocks or layers of Earth are worn away by natural forces such as wind or water, and the resulting broken-down pieces are transported to different locations.
2. Weathering: The process of breaking down rocks and other minerals through mechanical effects such as heat, water, ice, and other agents. Once broken down, erosion transports these particles to new locations.
3. Deposition: The filing or laying down of sediments being carried by water, air, or other agents. Sediments may be transported in forms such as pebbles, sad, mud, or as salts.
Geologic Impact: These dynamic processes reshape physical features across Earth's surface and provide evidence to understand past global conditions and natural phenomena.

Overview of the Geologic Time Scale: The geologic time scale is a standardized and organized system used by geologists (and critical to professions such as mining) to study Earth's history across specific periods using rocks, fossils, and geologic formations.
Foundational Geologic Principles and Key Pioneers:
- Nicolaus Steno (1699): Described two basic geologic principles:
1. Sedimentary rocks are filed and deposited in a horizontal manner.
2. Younger rocks are found on top of much older rocks, meaning that over time, older rock layers are covered by younger or more recent layers.
- James Hutton (1795) and Charles Lyell (early 1800s):
- James Hutton introduced the idea of uniformitarianism in 1795, which was later emphasized and expanded by Charles Lyell during the early 1800s.
- Principle of Uniformitarianism: Asserts that geologic processes operating today are uniform in both frequency and magnitude throughout geologic time.
- William Smith (1815):
- William Smith, a geologist and surveyor, created a geologic map of England in 1815.
- Principle of Faunal Succession: Demonstrates that observed strata of sedimentary rocks contain fossilized flora and fauna layered vertically in a specific order, which can also be identified horizontally across broad distances.

Structure of Geologic Time Units: Geologic time is divided systematically into nested categories:
- Eon: The broadest unit of geologic time, which is divided into eras.
- Era: Subdivisions of eons, which are divided into periods.
- Period: Subdivisions of eras, which are further divided into epochs.
- Epoch: A specific time period marked by notable events and distinct characteristics. Examples include the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene epochs.
The Quaternary Period:
- Classification: The Quaternary Period is the youngest period under the Cenozoic Era.
- Duration: Lasted for approximately $2.6\text{ million years}$ .
- Key Events: Characterized by significant climate changes, multiple ice ages affecting plant and animal distribution, and the evolution and development of modern human civilizations.