Modules 9-12 Flashcards
Uniformitarianism
Processes active in the environment today have operated since the beginning of earth’s history
Relative Time
Sequences based on the relative position of rocks above/below each other
Relative Dating
Can determine the order of events based on relative position of rocks
Principle of Superposition
In undisturbed strata of sediment or rock, the bottom later is oldest, the top layer is youngest
Principle of Original Horizontality
Sediments are deposited in horizontal layers; tilting and deformation happen later
Principle of Lateral Continuity
Layers initially extend in all directions; later events (e.g. erosion, faulting) can separate layers
Principle of Cross-Cutting
Intrusions, erosion, or faults are younger than the rock they cut through
Principle of Faunal Succession
Some fossil species occur in unique time intervals, age of rock may be determined from those fossils
Absolute Time
The actual time elapsed (usually in millions of years, for geologic time), most commonly measured using radiometric dating
Radiometric Dating
Some isotopes of some elements cannot stay together indefinitely; they undergo radioactive decay, determine age by measuring the amount of “parent” atoms relative to the amount of “daughter” atoms
Radioactive Decay
The nucleus of a “parent atom” decays to “daughter atoms” (releasing radioactive energy in the process)
Half-Life
The time needed for half of the parent atoms to decay
Geologic Time Scale
Summary timeline of Earth’s hsitory
Eon
The largest unit of geologic time, divided into eras, then periods, then epoch
Priscoan Eon
Began with Earth’s formation, part of the Precambrian supereon
Archaean Eon
Single-celled organisms developed, part of the Precambrian supereon
Proterozoic Eon
Current geologic eon (last 540 million years; roughly 12% of Earth’s history), began with Cambrian explosion: the appearance of abundant animal fossils
Paleozoic Era
(“old life”) the appearance of fish, amphibians, reptiles, vascular plants. Part of the Phanerozoic eon
Mesozoic Era
(“middle life”) dominated by dinosaurs and conifers; earliest birds, mammals, and flowering plants. Part of the Phanerozoic eon
Cenozoic Era
(“recent life”) age of mammals. Part of the Phanerozoic eon
Quaternary Period
Last 25 million years. Glacial and interglacial periods; anatomically modern humans. Divided into Pleistocene epoch and Holocene/Anthropocene epoch
Rock
Assemblage of minerals bound together
Mineral
Naturally occurring, inorganic substance with specific chemical formula, physical properties, and crystalline structure
Crystalline Structure
Atoms arranged in a repeating pattern, often visible to the naked eye
Mineralogy
Study of the composition, properties, & classification of minerals
Silicate Minerals
Contain silicon (Si) and oxygen (O). Makeup 95% of the earth’s crust. Rocks formed from silicates are usually strong and relatively resistant to weathering and erosion
Quartz
Made of silica (SiO₂); the second most common mineral in Earth’s crust. Color is often transparent or white, can be many colors. Common in granite rock, gneiss rock, and beach or desert sand. Common silicate mineral
Feldspar
Most common class of mineral in the earth’s crust. Contain aluminum, potassium, sodium, or calcium. Color is usually pink, cream, or grey. Common silicate mineral
Mica
Family of minerals that breaks into flakes and sheets. Shiny, partly transparent; clear, silvery-grey, green, brown, or black. Common silicate mineral
Mafic Minerals
Contain magnesium or iron, plus Silicon (Si) and Oxygen (O). Usually dark-colored. Common silicate mineral
Carbonate Minerals
Contain carbonate CO₃ (Carbon and 3 Oxygen atoms) bonded with another element. Commonly a cream or grey color; sometimes clear
Oxide Minerals
Contain Oxygen bonded with a metallic element, like iron, copper, or titanium
Sulfate Minerals
Contain sulfate SO₄ (Sulfur and 4 Oxygen atoms) combined with some other element
Sulfide Minerals
Metallic element and sulfur atom. Commonly form in veins of ore
Salt Minerals
E.g., halite (NaCl, table salt); fluorite (CaF₂, calcium fluoride)
Chemical Composition
Every mineral has a specific chemical composition. However, in some cases, two or more different minerals may have the same particular combination of elements
Mineral Properties
Hardness, cleavage/fracture, color and streak, luster, magnetism, feel, odor or taste, and chemical reaction
Luster
Surface sheen of a mineral
Color
Most easily observable property of a mineral
Streak
Color of powdered form when scraped against a porcelain plate. Usually consistent for a specific mineral
Hardness
Each mineral can scratch certain other minerals, but not vice versa
Mohs Hardness Scale
The hardness of a mineral can be tested by trying to scratch it with a known object or known mineral
Cleavage
The tendency of minerals to break along plane surfaces
Fracture
When minerals do not break on a clean plane but break in some other characteristic way
Magnetism
A few minerals are attracted to magnets and/or will attract a compass needle to them. E.g., magnetite, pyrrhotite
Chemical Reactions
Certain carbonate minerals ‘fizz’ if they are exposed to acid. E.g., hydrochloric acid or acetic acid (vinegar))
Fluoresence or Phosphorescence
Some minerals glow when exposed to black light, or after being exposed to sunlight
Taste or Feel
E.g., halite (sodium chloride) is main component of table salt, e.g., sylvite has a bitter taste, e.g., bentonite (a volcanic clay) has a creamy feel
Sound
E.g. phonolite has distinct sound when struck with a hammer
Igneous Rocks
Rocks formed directly from magma or lava (Ignis=”fire”)
Sedimentary Rocks
Rocks that have formed from the deposition and compression of rock and mineral fragments or by precipitation of material in solution, Sedimentum= “settling” (Latin)
Metamorphic Rocks
Rocks that have been created from transformation by heat and/or pressure from existing rocks
The Rock Cycle
Describes transitions between the 3 types of rocks
Magma
High-temperature molten rock, below surface
Lava
Molten rock, that has spilled onto surface
Intrusive Igneous Rocks
Formed from magma that cools and solidifies slowly, below the surface
Extrusive Igneous Rocks
Formed from lava that has reached the surface, as lava flows or volcanic eruption; cools quickly
Igneous Rocks are Classified Based on:
Mineral composition and grain size
Felsic Minerals
FELdspar and SIliCa; High in silica, aluminum, potassium, sodium; Low melting points, light-colored, and less dense
Mafic Minerals
MAgnesium and FerrIC (Iron) compounds; High in magnesium and iron, with some silica; High melting point, dark-colored, and more dense
Ultramafic Minerals
Very high in magnesium and iron
Large Grain-size
Intrusive igneous rocks cool slowly
Small Grain-size
Extrusive igneous rocks cool quickly
Obsidian
An extrusive igneous rock that cools very quickly (by contact with cold seawater), resulting in glass-like rock with no visible grains
Pumice
An extrusive igneous rock that has air pockets formed when gases escape from lava giving it a frothy texture; very lightweight; floats in water
Pluton
Any body of intrusive igneous rock
Batholith
Massive, irregular-shaped pluton, that melted and assimilated much of the rock structure it invaded
Sill
Magma spread between pre-existing strata, forming horizontal layers
Dike
Magma cut across pre-existing strata of rock, forming a vertical wall
Laccolith
Magma filled underground chamber, pushed overlying strata up forming a lens-shaped body of rock
Lithification
Process of cementation, compaction, and hardening that turns loose sediment into rock
Clastic Sedimentary Rock
Made from fragments or clasts of rocks which are compacted and cemented together
Chemical Sedimentary Rocks
Formed from dissolved minerals that are transported in solution and then recrystallize out as rocks
Organic Sedimentary Rocks
Contain deposits of plant or animal remains
Compaction
As layers of clastic sediment accumulate, lower layers are compressed by the weight of upper layers; amount of pore space decreases, as air and water are expelled
Cementation
Dissolved minerals precipitate out of solution, recrystallizing in pore spaces and forming a natural cement that holds the clasts together
Clasts
Fragments of rock or mineral; size determines how far they are transported before being deposited (large clasts settle out first)
Evaporites
Rocks that form as water evaporates, leaving salts behind; e.g., halite (table salt), gypsum, epsomite
Contact Metamorphism
Intruding magma heats and transforms (but doesn’t completely melt) adjacent rock
Regional Metaphorism
Tectonic activity creates intense pressure, altering the mineral structure
Rock Cycle: Below Surface
Heat and pressure
Rock Cycle: Above Surface
The exposed rock is weathered, transported, and deposited as sediment
Burial and Pressure
Compression and cementation, forming sedimentary rock
How to Tell Rock Types Apart: Igneous
Grains interlock, minerals look fused or crystallized together
How to Tell Rock Types Apart: Clastic Sedimentary
Grains touch but don’t interlock, held together by cement
How to Tell Rock Types Apart: Chemical Sedimentary
Interlocking grains, the difference from igneous in the types of minerals
How to Tell Rock Types Apart: Foliated Metamorphic
Twisted, folded, or swirled, or breaks into-thin layers
How to Tell Rock Types Apart: Non-Foliated Metamorphic
Harder to ID: often based on mineral groupings
Seismic Tomography
Image earth’s interior using earthquake waves
Inner Core
Solid (due to high pressure, in spite of high temp), mostly iron and nickel
Outer Core
LIquid (slightly lower pressure allows melting at high temp), mostly iron, with a little nickel
Earth’s Magnetism
Caused by the flow of liquid outer core around the solid inner core
Polar Wandering
The slow, erratic movement of magnetic poles, relative to the rotation axis
Lower Mantle
Solid, rigid rock- due to pressure
Upper Mantle
Solid, but not completely rigid
Asthenosphere
Plastic rock (solid, but deforms and flows like dough), some molten hot-spots (syrupy consistency)
Uppermost Mantle
Solid and rigid; part of lithosphere, less then 100 km thick
Crust
Outermost layer of earth
Oceanic Crust
Denser than continental crust, mostly basaltic rock
Continental Crust
Less dense than oceanic crust, more granitic rock, with some basaltic rock
Lithosphere
Outer shell of rigid rock, includes all of the crust, plus the uppermost mantle. Thicker under continents, thinner under oceans
Lithosphere/Asthenosphere Boundary
Based on rigid vs. plastic consistency. The rigid ____ moves around atop ____ is plastic
Crust/Uppermost Mantle Boundary
Based on a sharp change in density. The ___ is less dense than the ____.
Isostasy
The equilibrium state of the lithosphere floating on the asthenosphere
Mid-Ocean Ridge
Forms from upwelling magma, two sides of seafloor spread laterally apart
Subduction Zone
Ocean crust sinks under some other crust
Seafloor Spreading
As plates diverge, new oceanic crust will be continually added at the mid-ocean ridge
Theory of Plate Tectonics
Encompasses continental drift, sea-floor spreading, and movement of crustal plates
Divergent Plate Boundary
Plates spread apart; magma rises, forming new crust. Continental crust is uplifted and stretched; forms rift valley and block mountains
Convergent Plate Boundary
Plates collide, crust destroyed, mountain building
Transform Plate Boundary
Plate move past each other, crust neither formed nor destroyed
Continental Shields
Large, ancient, low-lying expanses of crustal rock that form the core of continental landmasses
Orogenic Belts
Regions of current or former mountain-building along margins of continental shields
Orogenesis
Process of mountain building along a n active continental margin, via volcanism and tectonic activity
Volcanism
Extrusion of magma at earth’s surface
Tectonic Activity
Bending (folding) and breaking (faulting) of the lithosphere, usually causing metamorphism
Orogeny
A mountain-building episode (over millions of years)
Active Continental Margins
Where two plates converge; tectonically active
Passive Continental Margins
Where continental crust and oceanic crust are on the same plate
Geomorphology
The study of the formation and evolution of earth’s landforms and landscapes, through endogenic and exogenic processes
Landform
A single, typical unit that forms part of the general topography. E.g., a hill, a mountain, a valley, a dune
Landscape
A collection of landforms (often the same type of landforms). E.g., mountain chain, series of ridges and valleys, a string of dunes
Endogenic Processes
Driven by internal forces of heat and convection in the earth; raise continental surfaces up
Exogenic Processes
Driven by external forces like rivers, waves, ice, and wind; Usually lower continental surfaces
The Geologic Cycle
Includes interactions among the hydrologic cycle, the rock cycle, and the tectonic cycle
Hydrologic Cycle
Movement of water; drives weathering, erosion, transportation, and deposition of rocks and minerals
Tectonic Cycle
Recycling and renewal of earth’s crust; the crust is destroyed at subduction zones, new crust is created at the rift zones and by upwelling
Rocks are subjected to 3 types of stress, which are expressed at the surface in different ways. The three types are:
Tension(or extension), Compression, and Shear
Whether a rock breaks depends on:
Composition of the rock and the amount of stress
Folding
Bending and deformation of beds (or layers) of rocks resulting from compressional forces
Monocline
Landform in which deformation results in beds that are inclined in a single direction, in a step-like bend; Occurs because of relatively small amount of compression
Anticline
Folded rock layer in arch- or ridge-like structure; Layers slope downward from central axis
Syncline
Folded rock layers in rough- or valley-like structures; Layers slope upward from central axis
Symmetrical Folds
Axial plane is vertical
Asymmetrical Folds
Beds in one limb dip more steeply than those in the others
Overturned Folds
Both limbs dip in same direction but one limb has been tilted beyond vertical
Four Combinations of Anticlines and Synclines
Anticlinal valley, anticlinal ridge, synclinal valley, and synclinal ridge
Identifying ridge of valley is based on:
Surface topography
Identifying an anticline or syncline requires:
Looking at the layers of rock, not just the surface topography
Plunging Folds
The axis (ridge of trough) of the fold dips (or plunges) downward at an angle
Hogsback Ridges
Sharp ridge formed from edge of gently tipped, resistant rock that overlies softer rock; the softer rock erodes, forming a steep cliff
Fault
A fracture in crustal rock, involving slippage of rock on one side of the fracture relative to the other side; Results when rock is stressed beyond its ability to remain a solid unit
The Resulting Fault of Compression Stress
Reverse or thrust fault
The Resulting Fault of Tension Stress
Normal or tension fault
The Resulting fault of Shear Stress
Strike-slip or transform fault
Reverse (Thrust) Faults
Caused by compression; causes shortening of crust as one block rides over the other; hanging wall is thrust up above the footwall; exposed part of hanging wall will typically erode.
Normal (Tension) Fault
Causee by tension (pulling); causes lengthening of crust as blocks pull outward; hanging wall is thrown down relative to the footwall.
Fault Scrap
Cliff formed by faulting
Overthrust Fault
A reverse/thrust fault in which the fault plane is nearly horizontal
Horst or Graben Landscape
Blocky landscape resulting from multiple normal faults acting in concert; often occurs in rift-zones with tension stresses on landscape
Horst
Upward-faulted block
Graben
Downward-faulted block
Strike-Slip Fault (Transform Fault)
Caused by lateral shearing; movement is lateral; horizontal layers are not displaced on opposite sides of fault
Left Strike-Slip Fault
Opposite side shifts to left
Right Strike-Slip Fault
Opposite side shifts to right
