Earth Science Reviewer

Evidence of Plate Movements

Continental Drift Theory

Originator: Alfred Lothar Wegener, a German polar researcher, geophysicist, and meteorologist, is credited with formulating this theory in the early 20th century.
Hypothesis (1912): Wegener proposed that continents slowly drifted apart from a single landmass called Pangaea (from the Greek for "All Earth"), which he believed existed over 200 million years ago, during the late Paleozoic and early Mesozoic eras.
Inspiration: He observed that the coastlines of South America and Africa fit together like pieces of a jigsaw puzzle, suggesting they were once connected.
Evidence: Wegener gathered geological and fossil evidence supporting his theory, notably from glaciation patterns, but he did not personally collect fossils.

Evidence Supporting Continental Drift Theory

A. Fitting of Continents

The precise fit of South America and Africa indicates they were once part of the same landmass before drifting apart due to tectonic activities over millions of years.

B. Fossil Evidence

Mesosaurus: Fossils of a freshwater reptile found in both South America and Africa demonstrate a substantial land connection prior to drifting.
Cynognathus: This extinct mammal-like reptile is represented in fossils found exclusively in South America and South Africa, dating back to the early to mid-Triassic period.
Lystrosaurus: Herbivorous reptiles from the early Triassic (approximately 250 million years ago) have been discovered in present-day Antarctica, India, and South Africa, indicating they thrived in a unified environment.
Glossopteris: This woody seed-bearing plant flourished during the Early Permian period, with fossils found across various continents, including Australia, South Africa, South America, India, and Antarctica, demonstrating a widespread ancient flora.

C. Rock Composition

Rock formations on opposite continents align precisely, indicating they were once connected. This includes specific examples, such as the Appalachian Mountains in North America and the Caledonian Mountains in Scotland, which share similar geological structures.

D. Climate Evidence

Evidence of glacier grooves and striations on continents that currently lack glaciers reveals they once experienced similar climatic conditions when they were part of a single landmass.

E. Coal Deposits

Major coal deposits found in regions such as North America and Europe indicate the existence of once lush, tropical vegetation that thrived in those areas when they were connected under Pangaea.

Movement of Plates

Tectonic Plates: Earth’s lithosphere is divided into massive plates, both continental and oceanic, which are responsible for various Earth's surface phenomena, including earthquakes, volcanic activity, and mountain building.
Tectonic Movements: Movement occurs primarily due to convection currents in the mantle, driven by heat from the Earth’s core, resulting in various geological features and continuous motion.

Types of Movements:

Collision: When two continental plates converge, they create mountain ranges through uplift.
Subduction: An oceanic plate sinks beneath a continental plate or another oceanic plate, leading to volcanic activity and trench formation.
Spreading: Plates moving apart at mid-ocean ridges create new oceanic crust.
Transform Faulting: Plates slide past each other, causing friction and often resulting in significant earthquakes.

Plate Boundaries

A. Convergent Plate Boundary

Subduction Zones: Areas where denser oceanic crust submerges beneath lighter continental crust, leading to geological formations, including mountain ranges such as the Andes and volcanic arcs like the Himalayas.

B. Divergent Plate Boundary

Occurs when tectonic plates move apart, forming mid-ocean ridges. The creation of new oceanic crust occurs as magma rises to fill the gap left by the diverging plates.

C. Transform Plate Boundary

Plates moving laterally past each other create friction, giving rise to earthquakes, exemplified by the San Andreas Fault in California.

Seafloor Spreading

Seafloor spreading is a geologic process of the movement of two oceanic plates, splitting apart from each other at a divergent plate boundary.
The hypothesis of seafloor spreading was largely formulated by Harry Hammond Hess, an American geologist, in the early 1960s. He proposed that new oceanic crust is created at mid-ocean ridges and slowly moves away from these ridges, leading to the movement of tectonic plates.
Evidence to Explain Seafloor Spreading
- The ocean floor: as two tectonic plates slowly separate, molten materials rises up from within the mantle to fill the opening.
- Mid – ocean ridges: these where slowly spreading ridges are the sites of tall, narrow underwater cliffs and mountains, and rapidly spreading ridges have a much more gentle slopes.
- Deep – sea trenches: are developed adjacent to subduction zones, where oceanic lithosphere slides back into the mantle.
- Geomagnetic reversals: reveal the continual process of seafloor spreading which separated the stripes in an orderly pattern, such as specific magnetism of basalt rock, determined by the Earth’s magnetic field when the magma is cooling.
- The age of seafloor: in seafloor spreading, the youngest oceanic crust is found at the ridges and progressively older crust is found in moving away from the ridges towards the continents
Evidence:
- Pillowed Rocks: Found on mid-ocean ridges, suggesting rapid cooling of lava during underwater eruptions.
- Magnetic Stripes: Symmetrical magnetic patterns on either side of mid-ocean ridges indicate periodic geomagnetic reversals over geological time.
- Age and density of oceanic crust increase with distance from mid-ocean ridges, with the oldest crust being approximately 200 million years old and found near deep-sea trenches.

Ocean Basins and Their Features

An Ocean Basin is defined as a large depression under the ocean surface, formed through various tectonic activities over millions of years.

Features:

Continental Shelf: The submerged border of a continent, typically a gentle slope leading down to the ocean floor.
Continental Slope: A steeply sloped area between the continental shelf and the deep ocean floor, where the ocean floor descends to greater depths.
Continental Rise: A region at the base of the continental slope that is formed by the accumulation of sediments.
Abyssal Plains: Flat, deep ocean floor regions that cover more than 50% of the Earth's surface, often consisting of thick layers of sediment.
Seamounts: Underwater mountains formed by volcanic activity that rise from the ocean floor but do not reach the surface.
Trenches: Deep, narrow depressions in the ocean floor, often associated with subduction zones, where one tectonic plate moves under another.
Mid-Ocean Ridges: Underwater mountain ranges formed by tectonic activity, where new oceanic crust is created as plates move apart.

Five Major Ocean Basins: Pacific, Atlantic, Indian, Arctic, and Southern, each exhibiting unique characteristics.

Pacific: The largest and deepest ocean basin, hosting numerous trenches like the Marianas Trench (the deepest point in the Earth's oceans).
Atlantic: Spanning approximately 29 million square miles with an average depth of about 12,881 feet, featuring the mid-Atlantic ridge.
Indian: Encompasses 26 million square miles, characterized by significant average depths and unique seafloor features.
Arctic: The smallest ocean basin, covered by sea ice and surrounded by land and shallow continental shelves.
Southern: Also known as the Antarctic Ocean, encircling Antarctica and defined by ocean currents and marine ecosystems.

Wilson Cycle

The Wilson Cycle describes the cyclical process of continental rifting, ocean basin formation, subduction, and mountain building over geological time. Proposed by geologist J. Tuzo Wilson in the 1960s, this theory illustrates how ocean basins open and close due to tectonic forces.

Stages of the Wilson Cycle:

Rifting: Continental lithosphere thins and fractures, leading to the formation of rift valleys and eventually new ocean basins.
Ocean Formation: As rifting continues, the rift valleys fill with water, creating new ocean basins.
Seafloor Spreading: New oceanic crust forms at mid-ocean ridges, and ocean basins expand, separating continental landmasses.
Subduction: Oceanic plates begin to subduct beneath continental plates or other oceanic plates, leading to geological activity such as earthquakes and volcanism.
Mountain Building: The remnants of the subducted plate can lead to the uplift of mountains, forming new mountain ranges as tectonic forces continue to act.
Closure of Ocean Basin: Eventually, ocean basins can close, leading to the collision and convergence of continental plates, reinitiating the cycle.

Measuring the Age of Earth

Principle of Uniformitarianism

It states that the physical, chemical, and biological laws that operate today have also operated in the geologic past.
This idea which led to modern geology begins in the late 1700s by James Hutton, a Scottish physician and a farmer, who published ‘Theory of the Earth’. In his work, he put a fundamental principle which is a pillar of geology today.

Deep Time concept is due to the process that shaped Earth’s surface such as:

Deposition: it is the geological process in which sediments, soil, and rocks are added to the landform or the landmass. Wind, ice, water and gravity transport previously weathered surface material where in the loss of enough kinetic energy in the fluid is deposited building up the layers of sediments.
Lithification: the process by which sediments turn into hardened rocks. There are three ways in which lithification can occur. The processes are called compaction, recrystallization and cementation.
Erosion: the geological process in which earth and materials are worn away and transported by the natural forces such as wind and water.

A. Relative Dating

Definition: It determines if an object/event is younger or older than another object/event from history.

Principles Used in Relative Dating

Superposition: States that in undeformed stratigraphic sequences, younger layers are deposited on top of older layers.
Original Horizontality: Suggests that sedimentary layers are originally deposited horizontally, allowing for accurate interpretations of geological history.
Unconformities: Refers to gaps in the geological record, resulting from processes such as erosion or non-deposition.
Law of Cross-Cutting Relationships: If a geological feature cuts through another, the feature that is cut is older than the one that cuts through it.

Major Methods of Relative Dating

Stratigraphy: The oldest dating method which studies the successive placement of layers. It is based on the concept that the lowest layer is the oldest and the topmost layer is the youngest.
Biostratigraphy: An extended version of stratigraphy where faunal deposits (remains and fossils of dead animals) are used to establish dating.
Cross-dating: Compares the age of fossils in layers with another layer.
Fluorine Dating: Talks about the bones that absorb fluorine from the groundwater.

Steno's Laws of Stratigraphy

Nicolas Steno:
- Father of Stratigraphy

Law of Superposition: In undeformed stratigraphic sequences, younger layers are deposited on top of older layers.
Law of Original Horizontality: Suggests that sedimentary layers are originally deposited horizontally, allowing for accurate interpretations of geological history.
Law of Lateral Continuity: States that layers of sediment initially extend laterally in all directions; therefore, they can be laterally correlated between different locations.
Law of Cross-Cutting Relationships: If a geological feature cuts through another, the feature that is cut is older than the one that cuts through it.

Types of Unconformity

Angular Unconformity: Occurs when tilted or folded sedimentary rocks are overlain by younger, flat-lying strata, indicating a period of erosion or non-deposition.
Disconformity: Refers to a gap in the geological record between two parallel sedimentary layers. This often indicates a period of erosion or a lack of deposition.
Nonconformity: Happens when sedimentary rocks are deposited on top of older metamorphic or igneous rocks, indicating a significant geological event that disrupted the original layers.
Paraconformity: A type of unconformity where layers of sedimentary rock are deposited without any significant interruption, but a gap in the geologic record exists within the sequence.

B. Absolute Dating

Definition: A scientific method used to determine the actual age of an event or object in years, primarily through techniques such as radiometric dating that relies on analyzing radioactive isotopes.
Isotopes: These are atoms that have the same number of protons but differ in neutron counts, making them useful in dating rocks and fossils.
Radiometric Dating: Utilized by geologists to establish the precise ages of boundaries on the geologic time scale.
Geologists find it difficult to determine the age of rocks because most rocks do not contain minerals that can be dated using radiometric dating .
Radioactive decay: It is occurring in a steady state; It breaks down unstable radioactive isotopes into stable isotopes
Alpha emission: A type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays’ into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two.
Beta emissions: Occurs when, in a nucleus with too many protons or too many neutrons, one of the protons or neutrons is transformed into the other.

Parent isotope: it is the unstable radioactive isotope.
Daughter isotopes: it is the stable isotope produced by the radioactive decay of the parent isotope.
Half-Life: This refers to the time required for half of a radioactive substance to decay; this concept is pivotal for accurately determining the ages of various geological and archaeological specimens. Use to determine if it is a parent isotope or a daughter isotope.

Major Methods of Absolute Dating

Radiometric Dating: This method uses the decay of radioactive isotopes to determine the age of materials. Examples include:
- Carbon-14 Dating: Used to date organic materials up to about 50,000 years old.
- Potassium-Argon Dating: Useful for dating volcanic rocks and ash, particularly in geological studies over millions of years.
- Uranium-Series Dating: Used primarily to date calcium carbonate materials (e.g., cave deposits, coral).
Dendrochronology: Also known as tree-ring dating, this method is based on the growth rings of trees, which can provide precise dating on an annual scale.
Thermoluminescence Dating: Measures trapped electrons accumulated in minerals since they were last heated, useful for dating ceramics and sediments.
Amino Acid Dating: Physical structures of living beings depend on the protein content in their bodies. The changes in this content in their bodies help determine the relative age of these fossils.