Renatas questions Flashcards
Uniformitarianism
The principle that the processes shaping Earth today (such as erosion, sedimentation, and volcanic activity) have worked in the same way throughout Earth’s history.
Key Idea: “The present is the key to the past.”
Proposed By: James Hutton in the late 18th century.
Example: Rivers eroding valleys today are assumed to have eroded valleys in the past in the same manner.
Importance: It provides a consistent framework for understanding Earth’s geological history.
actualism
A refinement of uniformitarianism, actualism states that the natural laws and processes we observe today have always been constant, but their rates or intensity may have varied over time.
Key Idea: While processes like erosion, deposition, and plate tectonics are consistent, their effects can differ based on circumstances (e.g., climate, tectonic activity).
Example: Erosion rates may have been higher during periods of heavy rainfall in Earth’s past compared to today.
Importance: It acknowledges that variations in environmental conditions can influence the outcomes of natural processes.
catastrophism
The theory that Earth’s features were shaped primarily by sudden, short-lived, and large-scale catastrophic events, such as earthquakes, volcanic eruptions, and floods.
Proposed By: Initially advocated by Georges Cuvier in the early 19th century.
Example: The formation of the Grand Canyon attributed to a massive, rapid flooding event (a catastrophist interpretation).
Modern View: While catastrophism once suggested these events were the only forces shaping Earth, modern geology recognizes catastrophes as significant but not exclusive contributors to Earth’s evolution.
James Hutton
A Scottish geologist (1726–1797), known as the “Father of Modern Geology.”
Contributions:
Developed the concept of uniformitarianism, proposing that the Earth’s features are the result of long-term processes that continue to operate in the present, like erosion, sedimentation, and volcanism.
Introduced the idea of a rock cycle, emphasizing that rocks are constantly recycled through natural processes.
Wrote the seminal work Theory of the Earth.
Importance:
Revolutionized geology by shifting the focus from catastrophism to processes observable today.
His work laid the foundation for understanding Earth’s immense geological timescale.
charles lyell
Who He Was: An English geologist (1797–1875), a key proponent of Hutton’s ideas, and a pioneer in geology’s development as a science
Contributions:
Popularized uniformitarianism in his book Principles of Geology, which influenced generations of scientists, including Charles Darwin.
Advocated that geological changes occurred gradually over millions of years, as opposed to sudden, catastrophic events.
Provided evidence for the continuity of geological processes, emphasizing that small, incremental changes shape Earth over time.
Importance:
His work helped establish geology as a discipline grounded in evidence-based science.
Played a crucial role in linking geology with evolutionary biology through his influence on Darwin.
Alfred wegener
A German meteorologist and geophysicist (1880–1930).
Contributions:
Proposed the theory of continental drift in 1912, suggesting that continents were once joined in a supercontinent called Pangaea and have since drifted apart.
Provided evidence such as:
The fit of continents (e.g., South America and Africa).
Fossil distribution (identical species on continents now separated by oceans).
Similar rock formations and mountain ranges across continents.
His ideas faced criticism during his lifetime due to the lack of a mechanism (later resolved with plate tectonics).
Importance:
Although initially dismissed, Wegener’s theory became the foundation of plate tectonics, one of the most significant scientific revolutions in geology.
Formation of Igneous Rocks
Igneous rocks form when magma (molten rock below the Earth’s surface) or lava (molten rock that reaches the surface) cools and solidifies. The process is categorized into two types depending on where the cooling occurs:
intrusive
extrusive
Intrusive (Plutonic) Igneous Rocks:
Formed from magma that cools slowly beneath the Earth’s surface.
Slow cooling allows large crystals to grow, resulting in a coarse-grained texture (e.g., granite, diorite).
Extrusive (Volcanic) Igneous Rocks
Formed from lava that cools quickly on the Earth’s surface.
Rapid cooling prevents large crystals from forming, resulting in a fine-grained or glassy texture (e.g., basalt, rhyolite, obsidian).
mafic rocks
Composition:
Low in silica (~45-55%).
High in iron (Fe) and magnesium (Mg).
Dominated by dark-coloured minerals like pyroxene, olivine, and plagioclase feldspar.
Characteristics:
Dark in colour (black or greenish).
Higher density.
Examples:
Intrusive: Gabbro.
Extrusive: Basalt.
Formation: Associated with oceanic crust and divergent boundaries (e.g., mid-ocean ridges).
felsic rocks
Composition:
High in silica (~65-75%).
Rich in aluminum, potassium, and sodium.
Dominated by light-colored minerals like quartz, feldspar, and mica.
Characteristics:
Light in color (white, pink, or pale gray).
Lower density.
Examples:
Intrusive: Granite.
Extrusive: Rhyolite.
Formation: Associated with continental crust and convergent boundaries (e.g., subduction zones).
metamorphism
is the process by which rocks undergo physical, chemical, and mineralogical changes due to heat, pressure, and chemically active fluids, typically without melting. The original rock (protolith) can be igneous, sedimentary, or another metamorphic rock.
Types of Metamorphism: contact metamorphism
Cause: High temperature from nearby igneous intrusions (magma)
Characteristics:
- Occurs in the contact zone around magma (baking effect)
- Produces non-foliated rocks due to a lack of significant pressure.
Examples:
Limestone → Marble
Shale → Hornfels
Types of Metamorphism: Regional Metamorphism:
Cause: High pressure and temperature over large areas, often due to tectonic plate collisions
Characteristics:
- Occurs at convergent plate boundaries.
- Associated with mountain building and subduction zones.
- Produces foliated rocks with banded or layered appearances.
Examples:
Shale → Slate → Schist → Gneiss (progressive metamorphism).
Types of Metamorphism: Hydrothermal Metamorphism
Cause: Interaction of rocks with hot, chemically rich fluids.
Characteristics:
- Common near mid-ocean ridges and geothermal areas.
- Alters rock composition through the introduction or removal of elements.
Examples:
Basalt → Serpentinite
Feldspar-rich rocks → Clay minerals
Types of Metamorphism: Burial Metamorphism
Cause: Increased pressure and temperature from deep burial of sediments in basins.
Characteristics:
- Occurs at depths of several kilometers.
- Often results in low-grade metamorphism (mild changes).
Examples:
Shale → Slate
Sandstone → Quartzite
Types of Metamorphism: Dynamic Metamorphism (or Fault-Zone Metamorphism)
Cause: High shear stress and pressure along fault zones.
Characteristics:
- Localized, affecting narrow zones.
- Produces rocks with a mylonitic texture due to intense deformation.
Examples:
Rocks in fault zones may become crushed or recrystallized into mylonite.
Types of Metamorphism: Shock Metamorphism (or Impact Metamorphism)
Cause: Sudden, intense pressure and heat from meteorite impacts.
Characteristics:
- Produces unique minerals like coesite and shocked quartz.
- Often forms glassy rocks called impactites.
Examples:
Quartz → Coesite
Rocks at Meteor Crater, Arizona.
Joint
Definition: A joint is a fracture in rock where there has been no significant movement of the rock on either side of the fracture.
Formation: Caused by stress such as cooling, unloading, or contraction in rocks.
Stress Types:
Tensile stress: Rocks are pulled apart, often leading to fractures in cooling lava or unloaded sedimentary layers.
Where They Occur:
Common in areas of cooling igneous rocks (e.g., columnar joints in basalt).
Found in sedimentary rocks due to unloading and erosion.
Fault
Definition: A fault is a fracture or zone of fractures in rock where there has been significant displacement of the rock on either side of the fracture.
Formation: Caused by differential stresses in the Earth’s crust, leading to the breaking and movement of rocks.
Stress Types:
Tensional stress: Pulling apart causes normal faults.
Compressional stress: Squeezing together causes reverse or thrust faults.
Shear stress: Lateral sliding causes strike-slip faults.
Where They Occur:
Plate boundaries:
Divergent boundaries: Normal faults (e.g., rift valleys, mid-ocean ridges).
Convergent boundaries: Reverse/thrust faults (e.g., subduction zones, mountain belts).
Transform boundaries: Strike-slip faults (e.g., San Andreas Fault).
Tensional Stress
Pulls the crust apart.
Creates normal faults.
Common in divergent plate boundaries (e.g., East African Rift).
Compressional Stress:
Squeezes the crust together.
Creates reverse faults or thrust faults.
Found in convergent boundaries (e.g., Himalayas).
Shear Stress:
Moves the crust in opposite lateral directions.
Creates strike-slip faults.
Found in transform boundaries (e.g., San Andreas Fault).
fault types
Normal Fault:
Hanging wall down
Tensional (pulling apart)
Divergent boundaries
East African Rift Valley
Reverse Fault:
Hanging wall up
Compressional (pushing together)
Convergent boundaries
Rocky Mountains
Thrust Fault:
Low-angle reverse fault
Compressional
Convergent boundaries
Himalayas, Andes
Strike-Slip Fault:
Horizontal motion (left/right)
Shear (lateral sliding)
Transform boundaries
San Andreas Fault
Oblique-Slip Fault:
Combination of vertical/horizontal
Mixed stress
Complex regions
New Zealand oblique faults
Anticline
An anticline is a fold where the rock layers arch upward into an “A”-shaped structure. The oldest rock layers are found at the core of the fold.
Appearance:
The limbs of the fold dip away from the crest.
Commonly forms ridges or elongated hills.
Cause: Compressional forces cause layers of rock to buckle and push upward.
Syncline
A syncline is a fold where the rock layers arch downward into a “U”-shaped structure. The youngest rock layers are found at the core of the fold.
Appearance:
The limbs of the fold dip towards the trough.
Commonly forms valleys.
Cause: Compressional forces cause layers of rock to sag downward.
Specific Categories of Folds
Based on Orientation:
Symmetrical Fold:
The limbs dip at equal angles on both sides of the fold axis.
Asymmetrical Fold:
One limb dips more steeply than the other.
Overturned Fold:
Both limbs dip in the same direction, but one limb is inverted.
Recumbent Fold:
The fold axis is nearly horizontal, and the limbs are almost parallel to each other.
Based on Scale:
Microfolds: Small-scale folds visible in thin sections or outcrops.
Mesofolds: Medium-scale folds seen in a single cliff or hillside.
Macrofolds: Large-scale folds that shape entire mountain ranges.
Based on Geometry:
Open Fold:
Broad and gently dipping limbs.
Tight Fold:
Closely spaced limbs with a sharp hinge.
Chevron Fold:
Angular folds with well-defined hinges.
Box Fold:
Folds with nearly flat tops and bottoms and steep limbs.
strike
The compass direction of a horizontal line on the surface of a tilted rock layer. It is perpendicular to the dip.
dip
The angle at which the rock layer inclines from the horizontal, measured perpendicular to the strike.
geologic-time table Eons Eras Periods
EON: Precambrian 4.000-543 m.y.a
- Archean 4.000- 2.500
4.000-3.400–> early
3.400-3.000–> middle
3.000-2.500–> late
- Proterozoic 2.500-543
2.500- 1.600–> early
1.600-900–> middle
900-543–> late
EON: Phanerozoic 543-now
- Paleozoic 543-248
- mesozoic 248-65.0
- cenozoic 65.0-now
