Earth Science 1G03 Midterm 1

Concentric Layers of The Earth

Crust, Mantle, Outer Core, Inner Core

Crust

0-40km thick, thickness of an apple skin vs total earth size

Continental Crust

20-40km thick, granitic rocks, rich in Si, Al, Na, and K (light elements)

Oceanic Crust

2-10km thick, basaltic rocks, denser than continental crust, rich in Fe and Mg

Isotasy

The condition of balance or equilibrium in which the crust floats on the mantle

Mantle

~2900km thick, molten, comprises most of the earths volume and mass, source of all crust and rich in Fe and Mg

Outer Core

~2240Km thick, molten, mostly Fe and Si

Inner Core

~1230km thick, solid, metallic core mostly Fe and Ni

Innermost Planets

Small and Rocky

Differentiation

Process of zonation (heavier metals sinking, lighter materials such as Si and O rising) due to accretion of debris and gravitational compression

Stromatolites

oldest evidence of life on earth, similar to algae (preserved in rock records)

Climate System

Atmosphere and Hydrosphere

Plate Tectonic System

Lithosphere, Asthenosphere, Deep Mantle

Geodynamo System

Outer Core, Inner Core

Convection Currents

Heat rises up, then cools and returns to bottom, creates new crust at mid ocean ridges

Lithospheric Plates

Crust and uppermost mantle

Theory of Plate Tectonics

Earth is divided into rigid plates which are in constant motion

Alfred Wegner

(1880-1930) proposed that continents drifted from one supercontinent (Pangea, 300-200MY ago)

Evidence of Continental Drift

Perfect puzzle fit, mesosaurus fossil in both South America and Africa, Climatic evidence from glacial formation

Mid Ocean Ridges

Submerged mountain regions usually characterized by a deep central rift valley

Central Rift Valleys

Tensional features formed by stretching of oceanic crust (long cracks)

Faults

fractures in bedrock along which rocks move relative to each other

Sea floor spreading Hypothesis

Ocean crust is created at mid ocean ridges, spreads laterally, descends back into the mantle at the deep sea trenches

Seismic Belts

Plate boundaries

Plates

Regions encircles by seismic belts are thin, rigid slabs of crust

Asthenosphere

Plates about 100Km thick glide over this part of the upper mantle

Divergent Boundaries

two plates moving away from one another (e.g mid oceanic ridges, crust created), volcanoes active, earthquakes common

Convergent Boundaries

two plates are colliding with another (crust is recycled)

Transform Boundaries

two plates sliding by one another horizontally; crust is neither created nor destroyed- usually high amounts of friction, pressure builds up and strong earthquakes common

Types of Convergent Boundaries

Ocean-Ocean, Ocean-Continent, Continent-Continent

Ocean-Ocean Convergence

Cooler oceanic plate subducts underneath island arcs, creating a deep sea trench. Partial melting generates magma, rises and flues island arc volcanoes

Ocean-Continent Convergence

Ocean crus subducts at shallow angle, volcanoes on bordering continental crust, creates mountains (i.e the andes)

Continent-Continent Convergence

Leads to extremely high topography (mountains), makes thick crust, volcanoes rare

Earthquake

Shock waves or vibrations within the Earth

How are earthquakes triggered?

Sudden slippage of rock along fault planes in the crust or mantle- release of accumulated strain energy

Types of Stress

Shear Stress, Tensional stress, compression stress

Foreshocks

Small, early quakes as rocks begin to fracture

Aftershocks

rocks along the fault adjust to transfer and strain

Focus

The centre point of an earthquake, underneath the epicentre

Epicentre

The point on the surface directly above the focus

Types of Waves

Body Waves (Primary and Secondary), Surface Waves (Love and Rayleigh)

P Waves

Travel through solid and liquid, series of expansions and compressions, fastest waves

S Waves

Travel through solid only, slower than P waves, rock vibration perpendicular to transport direction (do not penetrate beyond mantle)

Love waves

Side to side motion

Rayleigh Waves

convections in the rock, produces up and down motion on surface

Seismograph

Records seismic waves (surface waves are significantly larger than p and s waves on the seismogram)

Locating Earthquake Epicentre

P waves arrive before S waves, difference in arrival time increases with distance from the epicentre. Need at least 3 stations.

Richter Magnitude Scale

Logarithmic (i.e magnitude 5 is 10 times stronger than magnitude 4), energy released increases 32 times for each magnitude.

Factors influenceing destructiveness

Depends on depth of focus, rock types, proximity to population centres, types of structures, time of day, etc.

Mid Ocean Ridge Quakes

Shallow due to tensile stress

Transform Boundary Quakes

Shallow due to shear stress

Ocean-Continent Convergent Quakes

Compressive stress, shallow, medium and deep earthquakes

Composite Volcano

High silica content, stiff, viscous lava, highly explosive. Cone shape results in debris falling out of the vent near the volcano. Explosiveness due to buildup of high silica magmas (rhyolitic)

Shield Volcano

Low silica content, low viscosity, runny lava placid eruptions

Explosiveness of Lava

Viscosity is directly related to silica content. Basaltic magma (low silica) is less viscous, meaning less pressure. Rhyolitic magma (high silica) is more viscous, leading to more buildup and a larger explosion.

Mantle Plumes

Plume of hot mantle which rises and forms volcanoes on the surface

Hot Spot

Area of volcanic activity produce by a plume of magma rising from the mantle

Seamounts

Volcanoes below sea level

Guyots

Flat eroded top, was/is above sea level

Magnetic Reversal

A switch in the Earth's magnetic field, can be tracked by scientists

Felsic Volcanoes

Island arc, continental volcanic belt

Mafic Volcanoes

Mid ocean ridges, Active volcano over a hot spots

Flood Basalts

Very fluid basaltic lava that erupts on flat terrain and spreads out in sheets

Pahoehoe

ropy or smooth basaltic lava

Minerals

Naturally occurring, solid crystalline substances, inorganic, with definite chemical compositions and orderly internal atomic arrangements

Main Rock Forming Minerals

Oxygen and Silicon

Crystal Seed

mineral grows outward from seed- attachment of atoms to crystal face

Uninhibited Growth

Mineral grows in preferred crystal shape- euhedral

Inhibited Growth

Irregular Shape- anhedral

Hardness

Resistance to scratching

Cleavage/Fracture

How minerals cleave along parallel planes or how they fracture irregularly

Lustre

How a crystal face reflects light

-metallic, glassy, silky, dull

Colour

Not dependable, may vary even within the same mineral (trace elements)

Streak

the colour of the powder of a mineral when scratched on a porcelain plate

Density

ratio of a mineral's weight compared to an equal volume of water

Solidification

minerals will crystallize from magma when the conditions are right (temperature)

Precipitation

atoms dissolved in water bond together and separate out

Solid State Diffusion

movement of atoms to arrange into new minerals (metamorphic rocks)

Sedimentary rocks importance

constitute only 7% of the Earth's crust by volume but covers approximately 75% of the Earth's surface

Process of Sedimentary Rock formation

weather->transport->deposition->lithification

Weathering

physical and chemical alteration of rocks exposed to the atmospheric influences on the Earth's surface

Physical Weathering

Bedrock is broken into smaller fragments, composition of the minerals remains unchanged

Chemical Weathering

water and dissolved ions react with solid rock to eventually produce materials of different compositions

Transport

mechanisms through wind, water, glacial ice, coarsest particles closest to source area, finest particles travel farthest; greater distance resutls in smoother/rounded grains

Frank Slide

Rapid deposition of all sizes of particles=poorly sorted

Glacial Deposition

Continual deposition of all sizes of particles

Stream deposition

most efficient, particles get sorted into different sizes by the water

Lithification

the conversion of sediment into rock

Compaction

reduction in volume of sediments resulting from weight of newly deposited sediments above

cementation

a process by which precipitates bind together the grains of a sediment, converting it into a sedimentary rock

Beds/Strata

visually distinguishable layers of sedimentary rocks (youngest on top, oldest on the bottom)

Clastic Sediments

breccia, conglomerate, sandstone, siltstone, shale

Conglomerate

smooth, rounded grains, water transport

Sandstone

grains of sand held together with carbonate or quartz cement

Shale

platy, fine grained rock, splits along bedding planes

Chemical rocks

usually form as a result of metabolic activity of organisms (i.e carbonate reefs, limestones)

Rift Valleys

Rifting creates a topographic gradient, erosion of highlands into newly formed valley results in layers of sediment deposited in right valley

Continental Shelves

deposition of clastic sediment from continental rivers, margins of continents after rifting

Abyssal Plains

in the open ocean, a blanket of sediment covers the igneous rocks of the oceanic crust

Uniformitarianism

The present is the key to the past- laws that hold true today held true in the past