Earth History
Terms
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- Gneiss
- A rock in that intense pressure causes segregation of minerals into light and dark bands
- Phyletic Gradualism
- Gradual evolution, eventually rejected
- Silicate Minerals
- Always have silicon-oxygen tetrahedron
- Quartz
- No cleavage, varies in color, very durable
- Phanerozoic Eon
- 3 - Visible life, shelled organisms.
- Trace Fossils
- Evidence of the organisms activity
- Ferrous Iron Environment
- Due to high percentage of unoxidized organic matter, indicated lack of oxygen, ferrous iron
- Cement
- A chemical precipitate that crystallizes in the voids between grains following deposition.
- Geologic Time Scale
- Originally based on relative dating, type sections correlated world wide
- Divergent Plate Boundaries
- Two plates moving away from each other creating a ridge
- Chert
- Composed of microscopic quartz crystals
- Pyroxene
- 2 directions of perpendicular cleavage, dark green to black color
- Tectonic System
- Changing plates
- Chert
- Made of quartz, fossils, forms in the deep sea and limestone
- Porphyritic
- When phenocrysts are present in a matrix of smaller crystal. Represents a slow cool changing to a fast cool.
- Partial Melting
- Melting of ultra mafic mantle, happens on the ocean crust, creates mafic basalt
- Conglomerate
- Made of pebbles
- Casts
- A cavity left behind after an organism decays and is then filled in with new mineral material
- Continental Slope
- Bathyal
- Limestone
- Calcite, often forms from shells of marine organism, but may form inorganically as well
- Luster
- This is the way minerals reflect lights.
- Crystal Shape
- The shape a mineral may take as it grows, result of crystal structure.
- Calcite
- 3 directions of cleavage, color variable, and reacts with HCl
- Metamorphic Rocks
- Form due to pre-existing rocks changing due to temperature and pressure, chemically active fluids may be involved, no melting
- Perminalization
- Pores in the original hard part are filled with newly precipitated mineral material.
- Cratons
- The stable interior of a continent
- Scour Marks
- Currents flow across beds of sand creating scour marks.
- Pelagic Realm
- Nekton and Plankton
- The Core
- 2900 km to center
- Subduction Zone
- The area where one plate is being submerged under the other
- Infauna
- Living in the seafloor
- Hardness
- A measure of stregnth of the chemical bonds within the crystal structure. Measured using Moh's Hardness Scale
- Lithosphere
- Solid, rigid, thickness varies
- Recystallization
- Aragonite shells recrystallize to calcite
- Calcite
- 3 directions of cleavage, effervesces with HCl, many colors usually looks chalky
- Vestigal Structures
- Reduced structures inherited from ancestors
- Deep Sea Trenches
- Hadal
- Sphericity
- Degree of approach of a particle to a sphere
- Species
- Ability to breed and reproduce fertile offspring, variation exists within a species, difficult to apply to fossils
- Matrix
- Material deposited with the clast and then pressure caused it to squish together
- Radiometric Dating
- Uses half life to figure out age, decay generates heat. Parent to daughter isotope.
- Mohorovicic Discontinuity
- An area 5 - 70 km below the earth, wave velocity will increase as it passes through this area.
- Athenosphere
- Layer of soft and molten rocks, like silly putty
- Nekton
- swimmers
- C-14 Clock
- Half life of 5370 years, good for recent (50,000 or less) organic minerals
- Principle of Faunal Succession
- Fossils occur in the rock record in chronological order
- Plagioclase Feldspar
- Striations
- Orogenic Belts
- Elongated regions that border the craton
- Hydrologic System
- Erosion and deposition by water
- Feldspars
- A category of mineral with 2 directions of cleavage, color variable
- Mafic Silicates
- Dark color, higher density than felsic silicates, and it crystallizes at a high temperature
- Carbonate Sedimentary Rocks
- Form from the shells and skeletons of invertebrates found in warm shallow water.
- Rounding
- smoothing of edges and corners
- Facies
- A part of a rock that has characteristics from which we can infer the depositional environments
- Quartz
- Variable color, very durable, crystalline
- Mudcracks
- Sign of an area where there was once water
- Gutenberg Discontinuity
- Core/mantle boundary 2900 km below surface.
- Igneous Rocks
- Form from magma, first rocks to form
- Eolian
- Environments where wind is the agent of sediment transport and deposition
- Walther's Principle
- The vertical succession of facies corresponds to the later succession
- Pyrite
- Metallic, "fools gold," very heavy
- Rhyolite
- Extrusive and igneous, fine grain with microscopic crystals, light color
- Barrier Island
- Ocean side is high energy with sand, other side has silt and clay
- Hematite
- Brown streak color, despite outside color
- Mineral
- Naturally occuring, inorganic solid with a definite chemical formula, specific internal structure, crystalline solids
- Relative Dating
- Putting stuff in order based on principles of geology
- Convergent Plate Boundaries
- Two plates colliding and creating either a mountain range (2 continental) or a subduction zone (2 oceanic), or trench (oceanic and continental)
- Dolomite
- Similar to calcite, low effervescence
- Continental Slope
- Boundary between true continent and oceanic plate
- K-Ar Clock
- K -> Ar, Argon is a noble gas, 1/2 life of 1.25 billion years. Useful for dating old ass rock with K rich minerals
- Lord Kelvin
- Theory: Earth was originally all molten, tried to calculate age by how long it took to cool.
- Varves
- Layers in sedimentary rocks show season variations
- Lagoon
- May be hypersaline or brackish, low energy, low diversity
- Graded Bedding
- Flowing water sorts particles by size
- Principle of Original Horizontality
- Sedimentary rocks and some extrusive igneous rocks are originally formed as layers
- Halite
- SALTTTT
- Homologous Structure
- Body parts having the same origin but adapted for different purposes
- Sandstone
- Made of sand
- Sorting
- The geologic term for the degree to which sedimentary rocks are uniform by particle size.
- Angular Uncomformity
- Rock layers and erosion surfaces do not parallel each other
- Slate
- Clay minerals in a shale re-align and recrystallize into new minerals
- Platforms
- Regions where ancient shield rocks are covered by flat lying or gently warped sedimentary layers
- Taphonomy
- The study fossil preservation
- Radiometric Dating
- Using the decomposition of Radioactive Isotopes to determine a rocks age. Decay generate heat. 1/2 life determines the age. Parent --> Daughter
- Formation
- A distinctive rock unit that has recognizable characteristics with other distinctive units above and below
- Epifauna
- living on seafloor
- Plankton
- Floaters
- Benthic Realm
- Epifauna and Infauna
- Regional Metamorphism
- Over a wide area, wide range of temperature and pressure, associated with mountain building
- Phanerozoic Eon
- Visible life, shelled organisms. Lasted from 542 to present. 3 Eras: Paleozoic, Mesozoic, and Cenozoic. (3)
- Onlap Sequence
- Coarser sediments are covered by finer ones
- Specific Gravity
- Mineral specimens feel heavier than others.
- Lacustrine
- Lake deposits with low energy and fine sediment (PLAYA lake)
- Amphibole
- 2 directions of cleavage at 60 degrees and 120 degrees, green ---> black
- Principle of Inclusions
- A rock in a rock is older than the rock it is inside of
- Ocean Floor
- Abyssal
- Transforming Plate Boundaries
- Two plates passing by creating fault lines
- Mantle Plume
- A very hot flare from the earths core that creates volcanoes or mass
- Proterozoic Eon
- 2 - 2.5 billion to 542 million years ago. Free oxygen accumulates, extensive glaciation, progression of evolution
- S waves
- Particles perpendicular to wave directions do not move through liquids, secondary waves
- Ice Layers
- Snow compresses after each season into ice layers.
- Coal
- Composed of carbon from buried plant material
- Unaltered Soft Parts
- Extremely rare, usually temporary
- Unaltered Hard Parts
- Bones, etc, usually changed in some way.
- Poor Sorting
- Broad range of particle size
- Halley and Joly
- Theory: Ocean as old as the earth, believed that the ocean started out freshwater and tried to calculate the earths age by determining how long it took it to get salty.
- Benioff Zone
- Area in subduction zone where deep focus earthquakes come from
- Felsic Silicates
- Light color, low density, crystallizes out of magma at low temp, especially abundant in continental crust
- Evaporite Minerals
- 3 directions of cleavage, salt etc
- Polymorphism
- 2 minerals with the same chemical structure but different crystal structures.
- Principle of Uniformitarianism
- Present is key to the past, James Hutton
- Biotite Mica
- One direction of cleavage, dark
- Punctuated Equilibrium
- Stasis punctuated by suddent appearance of new species, new species arise as gradual change occurs to isolated population
- Offlap Sequence
- Coarser nearshore sediment tends to lie above finer sediments
- Continental Shelf
- Sublittoral and littoral
- Paleozoic Era
- Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pensylvanian, Permian (Campbells Onion Soup Delights Many Poor People)
- Gypsum
- Fire retarded, white, soft, chalky
- The Mantle
- Below crust to 2900 km
- Ferric Iron Environment
- oxygen rich environment colored brown or red
- Crystal Shape
- The geometric shape which reflects its internal crystal structure.
- Vesicular
- Formed from bubbling lava that cools rapidly
- Archean Eon
- 4b-2.5b, evolution of life, continents form. (1)
- Discomformity
- Sedimentary layers followed by erosion and more sedimentary layers
- Carbonization
- Volatile elements are driven off leaving Carbon behind
- Cross Bedding
- Layers deposited at angles
- Geologic Time Scale
- Originally based on relative dating, type sections correlated world wide
- Shield
- A large area of exposed ancient crystalline rocks
- Pre-Archean Eon
- 0 - Formation of the earth (4.6 billion years ago) to formation of first rocks (4 billion years ago)
- Olivine
- Olive green hard material
- Shale
- Made of compressed layers of mud
- Streak
- The color left on the streak plate by minerals which are softer than 7 on the Moh's Hardness Scale. No matter the color minerals always have the same streak.
- Symmetrical Ripple Marks
- Indicates wave
- Granite
- Coarse with visible crystals, light color, intrusive
- Catastrophism
- Multiple creations, multiple floods
- Contact Metamorphism
- Heat and fluids escape from cooling magma
- Quartzite
- Forms when tiny quartz in quart sandstone recrystallize to larger ones
- Streams and Rivers
- Clastic sedimentary rocks from conglomerate to shale deposited on stream
- Diorite
- Course with visible crystals, intrusive, medium color
- Mold
- Impression of original organism, internal and or external
- Follation
- In metamorphic rocks, this process creates parallel alignment of mineral grains indicate high pressure
- P waves
- Compressional waves, lower velocity in H20
- Aragonite
- Polymorph of Calcite, secreted by many shelled organisms, less stable than calcite
- Ichnology
- The study of trace fossils
- Halley and Joly
- Theory: Ocean was originally freshwater and is as old as the earth, tried to calculate age by how long it took the oceans to become saltwater
- Metastable Minerals
- Minerals formed under different temperature and pressure regimes than that at the earth's surface, and slowly decompose once at surface level.
- Color
- Unreliable as it varies widely.
- Lord Kelvin
- Theory: Earth was once all molten rock, tried to calculate age by determining cooling rate
- Mesosphere
- Very high pressure to 2900 km
- Glacial
- Environment where there is fine sediment, drop stones
- Principle of Super Position
- Old rock layers on bottom, new ones on top.
- Limestone
- Very variable, composed of calcite
- Principle of Cross Cutting Relations
- Igneous intrusions, faults, and uncomformities are younger that rocks they cut.
- Clay Mineral
- Tiny sheet silicates, absorbent
- Pre Archaen
- (0) formation of the earth (4.6 billion) to formation of first rocks (4 billion). No record
- Archaen Eon
- 1 - 4 billion to 2.5 billion years ago. Evolution of life and forming of continents
- Crystal Structure
- The way elements are bonded together within the mineral.
- Proterozoic Eon
- 2.5-542, (2) Free Oxygen accumulates, marked by extensive glaciation, evolution progresses
- Asymmetrical Ripple Marks
- Indicates current (ex ancient river bed)
- Uncomformities
- Buried erosion surfaces, interpretation of past events can e based on absence of layers as well.
- Surface Waves
- Less depth, particles move in circular motion, travel slowly on earth's surface.
- Obsidian
- Glassy, extrusive, dark black color
- Varves
- Layers found in sedimentary rocks that show seasonal variations
- Basalt
- Dark, fine with microscopic cystals, mafic silicate
- Muscovite Mica
- 1 direction of cleavage, light color in thin sheet
- Fracture
- This is the way a mineral breaks when it does not have cleavage
- Schist
- Large, aligned platy minerals give it a shiny layered look
- Deep Sea Environment
- Extremely fine clastic sediment, microscopic shells, dropstones
- Marble
- Forms when tiny calcite crystals in limestone recrystallize to larger ones
- Rock Units
- Bodies of rock having distinctive features without regard to to time boundaries
- Fragmental
- Volcanic ash and glass, happens in explosive erruptions
- Alluvial Fan
- Stream transported materials accumulate quickly when rapidly flowing streams emerge from a mountainous area onto a flat plain
- Cleavage
- When a mineral breaks, it breaks along planes of weakness in its crystal structure.
- Delta Environment
- Accumulations of sediemnt that form where a stream flows into relatively quiet water
- Tuff
- Pyroclastic, fragmental, volcanic ash and glass
- Absolute Dating
- Find exact age of rock due to radioactivity by the breaking down of isotopes
- Sedimentary Rocks
- Form from physical and chemical weathering of pre-existing rock, have clast
- Clasts
- Individual particles or fragments derived from the breakdown of existing rocks
- Nonconformity
- Rocks below the erosion surface are intrusive igneous or metamorphic
- Pumice
- Vesicular, extrusive, and light color
- Replacement
- New mineral material replaces old
- K-AR Clock
- Decomp. of Potassium (K) to Argon (Ar) 1/2 life of 1.25 billion years, useful for old rocks with K minerals
- Grain Orientation
- Aligned grains give clues to current directions
- Orthoclase Feldspar
- 2 directions of cleavage, perthites (feathery lines)
- Turbidites
- Deposits left by turbidity currents
- Ice Layers
- Snow compresses into ice every season, shows relatively recent environment info
- C-14 Clock
- Carbon dating clock, half life of 5370 years, good for recent (50,000 years or less) organic minerals
- Scoria
- Vesicular, extrusive, and dark color
- The Crust
- Outermost layer, made up of the highest elements
- Muscovite Mica
- One direction of cleavage, light