Geology and Continental Drift Quiz

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Questions and Answers

What geological feature is primarily formed due to tensional forces at the ridge crest?

Submarine canyons

Continental slopes

Oceanic trenches

Rift valleys (correct)

What causes oceanic crust to sink beneath a continent or island arc?

Cooling and increased density of rock (correct)

Decrease in rock density

Subduction of continental margins

Formation of abyssal plains

What is the primary function of submarine canyons in oceanic systems?

Forming mid-ocean ridges

Creating new oceanic crust

Delivering continental sediments to abyssal fans (correct)

Reducing ocean sediment temperatures

What is characterized by gently sloping wedges of sediment extending from the base of the continental slope?

Continental rise Signup and view all the answers

Which of the following best describes abyssal plains?

Extremely flat ocean floor areas beyond the continental rise Signup and view all the answers

What is the primary implication of paleoclimate belts in relation to continental drift?

Paleoclimate belts suggest polar wandering as evidence for continental drift. Signup and view all the answers

Which theory explains the distribution of land-dwelling reptiles across separated continents?

The existence of land bridges connecting the continents. Signup and view all the answers

What was a significant criticism of Wegener's proposed mechanism for continental drift?

It relied heavily on centrifugal forces, which were deemed unconvincing. Signup and view all the answers

Which of the following statements best describes the concept of polar wandering?

It suggests that the poles remain constant while continents drift. Signup and view all the answers

Which supercontinent included South America, Africa, Antarctica, Australia, and India?

Gondwanaland Signup and view all the answers

During which geological period were coal beds deposited in northern continents, indicating warm swampy environments?

Late Paleozoic Signup and view all the answers

How can polar wandering be explained in relation to continental drift?

By both polar movement and continental drift occurring simultaneously. Signup and view all the answers

Which of these factors was NOT typically cited to explain skepticism toward continental drift?

A clear absence of fossil records supporting continental drift. Signup and view all the answers

What is the main significance of paleomagnetism in the study of continental drift?

It assists in determining the historical positions of continents. Signup and view all the answers

Which evidence suggests that continents were once joined together as Pangaea?

Identical glacial striations found across continents. Signup and view all the answers

How does seafloor spreading support the theory of continental drift?

It demonstrates the conveyor belt movement of tectonic plates. Signup and view all the answers

What role do steeper dip angles play in paleomagnetic studies?

Suggesting proximity to the magnetic poles during formation. Signup and view all the answers

What primary geological feature is associated with the concept of deep mantle convection?

Mid-oceanic ridges. Signup and view all the answers

What is the estimated time frame during which continents have been in motion?

2 to 4 billion years. Signup and view all the answers

What does the term 'apparent polar wander' refer to?

The perceived movement of continents in relation to magnetic poles. Signup and view all the answers

What geological evidence supports the fitting of continents into a combined landmass?

Similar isotopic ages and sequences of rock types. Signup and view all the answers

Study Notes

Endogenic Processes of the Earth

Endogenic processes are internal processes that shape Earth's surface.
Plate tectonics is a unifying theory.
Earth's surface is composed of several large, thick plates that move slowly changing in size.
Plates interact at boundaries, engaging in intensive geological activity (moving away, towards or past each other).
The theory is based on continental drift and seafloor spreading hypotheses.
Alfred Wegener observed similar late Paleozoic rocks and fossils in South America, Africa, India, Antarctica, and Australia.
Evidence also includes Glossopteris, Lystrosaurus, and Cynognathus fossils found on five continents.
Pangaea was a supercontinent proposed by Wegener.
Laurasia was the northern supercontinent.
Gondwanaland was the southern supercontinent.
Evidence includes glacial patterns on southern continents and coal beds in northern continents.

Plate Tectonics: The Unifying Theory

Plate tectonics encompasses the movement of Earth's lithospheric plates.
Plates move relative to one another, interaction at their boundaries impacting geologic activity.
The major plates are: North American, South American, Pacific, African, Eurasian, Australian-Indian, Antarctic, and various smaller plates.
Plate boundaries are classified as divergent, convergent, and transform boundaries based on plate movement.

Evidence from Paleomagnetism

Paleomagnetism studies ancient magnetic fields.
Magnetite mineral in cooling lava preserves the Earth's magnetic field direction.
The angle of the magnetic field lines, known as inclination, indicated the distance to the magnetic North pole.
Rocks with increasing age indicate magnetic poles increasingly far from present locations.
Polar wander curves for different rocks provide additional information regarding continental movement.
Matching polar wander paths supports the concept of continental drift.

Geologic Evidence for Continental Drift

Fitting continents, isotopic ages, glacial striations, and rock types provide geologic evidence for continental drift.
Paleomagnetic data details the direction and rate of movement.
Pangaea broke apart approximately 200 million years ago, but the movement of continents is a long historical process.

Seafloor Spreading

Seafloor spreading is the concept of the seafloor moving like a conveyor belt.
Hot mantle rocks rise beneath mid-oceanic ridges.
Decompression melting occurs, resulting in the movement of molten rock away from the ridges.
Rift valleys form at the crest of the ridge due to tensional forces.
Rocks cool and become denser, sinking back into the mantle at oceanic trenches.
The overall young age of sea floor rocks (<200 million years) supports this model.

Fracture Zones and Transform Faults

Mid-oceanic ridges are offset by fracture zones.
Transform faults are fracture zone segments located between offset ridge crests.
Relative motion along these faults is a consequence of seafloor spreading from adjacent ridges (strike slip movement).

Measuring Plate Motion Directly

Plate motion can be measured using satellites, radar, lasers, and global positioning systems.

Divergent Plate Boundaries

Plates move apart at divergent boundaries.
These boundaries are typically marked by rifting, basaltic volcanism, and eventual ridge uplift.
New oceanic crust is created at divergent boundaries.
Examples include the mid-Atlantic ridge.

Transform Plate Boundaries

Plates slide past each other at transform boundaries.
Transform faults often connect two offset segments of mid-oceanic ridge.
Found in between the mid-oceanic ridge and trenches.
The movement is predominantly horizontal and parallel to strike of the fault plane.

Convergent Plate Boundaries

• Plates move toward each other at convergent boundaries.

Three types based on plate types: ocean-ocean, ocean-continent, continent-continent
Result in features like oceanic trenches, Benioff zones, volcanic arcs, and mountain belts.

Do Plate Boundaries Move?

Plate boundaries can change over time, migrating toward or away from subduction zones or abruptly jumping to new positions in response to changes in plate motion.

Can Plates Change Size?

Plates can change size over time.
New seafloor is added to the trailing edge as seafloor spreads, increasing the size of certain continents.
Other plates might get smaller as their leading edges are subducted.

What Causes Plate Motions?

Mid-oceanic ridges are hot and elevated, while trenches are cold and deep.
Ridge crests have tensional cracks.
Subducting plates move downward into the mantle.
Mantle convection sets up a ridge-push and slab-pull mechanism—driving plate movement and affecting formation of mid-ocean ridges and trenches.

Ridge Push, Slab Pull, and Trench Suction

Ridge Push – new plate cools and thickens away from the divergent plate boundary; gravity pulls it downward.
Slab Pull – Subduction of cold, dense oceanic lithosphere pulls trailing part of the plate into the mantle, due to gravity.
Trench Suction – force pulling plates into trenches due to dense sinking plate segment in the mantle and pulling on overlying plates.

Mantle Plumes and Hot Spots

Mantle plumes are narrow columns of hot mantle rock.
Mantle plumes rise through the mantle and cause stationary hot spots at the Earth's surface.
These spots lead to volcanic activity.
Examples include Hawaii and Yellowstone.
Rifting and divergent boundaries can be new forms of plates and/or the movement of existing plates.

Hot Spot Volcanism

Mantle plumes create chains of volcanoes as the plate moves over a stationary mantle plume.
The age of the volcanoes tracks the direction and rate of plate motion.
An example is the Hawaiian Island chain.

Emperor Seamounts of Hawaii

This chain shows the movement of the Pacific plate over a period of millions of years.

Earth's Interior & Geophysical Properties

Earth’s interior must be studied indirectly due to it's vastness and inaccessibility.
Geophysical property information is used to understand the structure of the Earth's interior.

How Is Earth's Interior Studied?

Indirect methods are used to study the Earth's interior.
Seismic wave analysis provides valuable data on Earth's structure and composition.
Seismic wave analysis includes seismic reflection, and seismic refraction properties to help interpret.

Evidence from Seismic Waves

Seismic waves, caused by earthquakes, pass through the Earth and provide evidence about the interior's composition and structure.
Reflection and refraction of Seismic waves create differing paths through layers of the Earth, depending on the seismic velocity.

Earth's Internal Structure

The Earth has three main layers: crust, mantle, core.
The crust, thin, forms Earth's surface.
The mantle is a transition layer between the crust and the core.
The core is the center of the Earth and composed of iron and nickel.

Earth's Internal Structure: The Crust

Oceanic crust has an average thickness of 7 km.
Seismic waves travel at 7 km/sec through oceanic crust.
Oceanic crust is composed of mafic rocks like basalt.
Continental crust has an average thickness of 30 to 50 km.
Seismic waves travel at 6 km/sec through continental crust.
Continental crust is composed of felsic rocks like granite.

Earth's Internal Structure: The Mantle

The mantle contains dense, ultramafic rocks.
The crust and the upper mantle make up the lithosphere.
The lithosphere is the solid, brittle outer shell of the Earth.
The mantle has a plastic low-velocity zone—the asthenosphere—allowing plate movement, located beneath the lithosphere.

Seismic Shadow Zones

Earthquake vibrations produce seismic waves which follow predictable paths through the Earth.
Seismic waves are refracted and reflected at boundaries.
Some areas have no direct seismic waves; these regions are the seismic shadow zones, which show differing behavior when passing through the Earth.
Studying the absence of seismic waves helps scientists determine the properties of the Earth's core.

Earth’s Internal Structure: The Core

The Earth’s core is an iron-nickel alloy with traces of lighter elements.
Its density is approximately 10-13 grams/cubic centimeter.
Both astronomical and seismic wave data support its composition.

The Core-Mantle Boundary

The D” layer marks the base of the mantle.
Seismic velocities, density, and temperature differ significantly across this layer.
An example of this is the Ultralow-velocity Zone (ULVZ).

Earth’s Temperature and Geothermal Gradient

Temperatures increase with depth into the Earth.
The rate of temperature increase with depth is known as the geothermal gradient.
The gradient is steady beneath the lithosphere.

Heat Flow

Heat flow is the gradual loss of heat from the Earth's surface.
Sources of heat include original heat and radioactive decay.
Heat flow is higher near the surface where magma is present.
Magma produces heat, and radioactive decay within crust generates heat

Geologic Structures

Geologic structures are patterns formed within the Earth due to forces like stresses within the Earth.
Changes in rock shapes or orientation are evident due to stress and/or strain.
Structural geology studies the arrangement of rock, forces, and causes of the shapes.

Tectonic Forces at Work

Stress is force acting per unit area.
Types of stress are compressive, tensional, and shear.
Strain is a change in size or shape due to stress.
Geologic structures indicate the type and rate of stress.

How Do Rocks Behave When Stressed?

Rocks can behave as elastic, ductile, or brittle.
Properties of materials (elasticity, ductility, or brittleness) depend on factors such as stress application levels, and rate of stress change.
Rocks respond differently to stress depending on the type of rock, temperature, and pressure.
Elastic limit is the stress limit at which materials that were deformed return to their original shapes.

Folds

Folds are wave-like bends in layered rocks.
Types of folds include anticlines (upward-arching) and synclines (downward-arching).
Folds form due to stresses usually from compression.
Folds, when observed in context with other geologic formations, indicate stress, strain or direction of forces and magnitudes within geologic layers.
Key features like the axial plane, hinge lines, and limbs help interpret folds.
Plunging folds deviate from a horizontal hinge line.

Geometry of Folds

Domes and basins are geological structures showing how rocks have been stressed.
Domes have beds dipping outward from a central point—sometimes a doubly plunging anticline.
Basins have beds dipping towards a central point— sometimes a doubly plunging syncline.

Interpreting Folds

Open folds have gently dipping limbs.
Isoclinal folds exhibit parallel limbs.
Overturned folds display limbs dipping in the same direction.
Recumbent folds are overturned folds that are horizontal or very close to horizontal.

Joints

Joints are fractures in bedrock without discernible movement.
They form due to various forces, including stress release and contraction during cooling.
Types of joints include columnar joints (from cooling lava flows) and sheet joints (from pressure release).
Joint sets are groups of parallel or closely spaced joints.

Faults

Faults are fractures in bedrock and rocks where movement has occurred, due to tectonic forces.
Dip-slip faults have motion parallel to the dip of the fault plane— vertical motion of fault blocks.
Examples of dip-slip faults are normal and reverse faults.
Strike-slip faults have predominantly horizontal motion along the strike of the fault plane.
An example is oblique-slip faults exhibiting both vertical and horizontal movement.

Normal Faults

Normal faults form due to tensional stress.
The hanging-wall block moves downward relative to the footwall.
Graben is a fault block that drops between two normal faults.
Horst is a fault block that rises between two normal faults.

Features of Normal Faults

Grabens are fault blocks bounded by normal faults that drop down due to tensional stress.
Rifts form grabens associated with divergent plate boundaries due to tensional stress.
Horsts are fault blocks uplifted between normal faults.

Reverse Faults

Reverse faults form due to compressional stress.
The hanging-wall block moves upward relative to the footwall.
Thrust faults are reverse faults with dip angles less than 30 degrees from horizontal.

Strike-Slip Faults

Strike-slip faults have horizontal movement, parallel to the fault's strike.
Two types are right-lateral and left-lateral, describing the offset direction when viewing the fault.

The Sea Floor

The seafloor is the bottom of the ocean and comprises various features like ridges, trenches, and plains.

Origin of the Oceans

Oceans originated primarily from volcanic degassing of water vapor.
As the Earth cooled, water vapor condensed and fell as rain, creating the oceans.

Features of the Sea Floor

Passive continental margins comprise the continental shelf, slope, and rise extending to the abyssal plain.
Active continental margins consist of continental shelves and slopes that extend to a deep oceanic trench.
Mid-oceanic ridge systems are undersea mountain chains, mostly formed of basalt.
Seamounts are conical seamounts rising from the deep ocean.

Continental Shelves and Slopes

Continental shelves are gently sloping, shallow platforms.
Continental slopes are relatively steeper slopes extending from the shelf into the abyssal plains.
Young sediments commonly cover the continental shelves, while sedimentary deposits and turbidity currents sculpt the slopes.

Submarine Canyons

Submarine canyons are V-shaped valleys that run across continental shelves and continental slopes.
They deliver continental and/or sediment to abyssal plains due to turbidity currents which can be initiated by various triggers and associated erosion.

Passive Continental Margins

Passive margins contain a continental shelf, slope, and rise extending to the abyssal plain.
The continental rise is a gently sloping region of accumulated sediments from continent and turbidity currents, extending downward to the abyssal plane.
The continental rise ends at the abyssal plain.
The abyssal plain is a flat region beyond the continental rise.
Characterized by very shallow slopes, nearly absent slope, and abundant turbidity currents.

Active Continental Margins

Active continental margins include a shelf, slope, and oceanic trench.
Oceanic trenches are narrow, deep troughs that are parallel to the edge of continents.
These are the deepest parts of oceans.
The Benioff zone is an area of earthquake foci, located at trenches.
Volcanoes often are found atop the Benioff Zone.
Typically coincide with low heat flow and large negative gravity anomalies.

Mid-Oceanic Ridges

Mid-oceanic ridges are giant undersea mountain ranges.
They encircle the globe, resembling seams on a baseball.
They have a rift valley down the crest (characteristic tensional stress).
The ridges are mostly made from young basalt flows.
Seismic activity (shallow earthquakes), extreme heat flow and presence of hydrothermal vents and unique communities of biological organisms are associated with oceanic ridges.

Reefs

Reefs are wave-resistant ridges formed by coral, algae, and other calcareous organisms.
Coral reefs are found in warm, shallow, sunlit, sediment-poor waters.
Three types of reefs are observed: fringing reefs (encircle islands), barrier reefs (parallel coastlines), and atolls (rim lagoons).

Sediments of the Sea Floor

Terrigenous sediments are land-derived sediments that reach the seafloor.
They comprise continental rises and abyssal plains.
Pelagic sediments are fine-grained sediments derived from the ocean (wind, and organisms).
These are rarely found in mid-ocean ridges.

The Age of the Sea Floor

Deep-sea floor rocks are less than 200 million years old.
Continents have rocks older than 4 million years.
Seafloor spreading is a key element in the theory of plate tectonics helping to explain the formation and movement of seafloor, along with its age.

Reference

Plummer, C., D. Carlson, and L. Hammersley. Physical Geology, 17th ed. McGraw Hill.

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Test your knowledge on geological features and the concept of continental drift. This quiz covers various aspects of geology, including oceanic systems, sediment wedges, and paleoclimate implications. Challenge yourself with questions about tectonic forces and historical supercontinents.