Geology ch 2

The processes of planet formation created tremendous quantities of heat, which fundamentally changed Earth. The heat that transformed Earth came primarily from:

1. Impact energy(heat of accretion). 2. Decay of radioactive isotopes. 3. Gravitational energy. 4. Differentiation into layers (heat of differentiation).

Radioactive isotope definition

Unstable element containing excess subatomic particles that are emitted to achieve a smaller, stable atom.

Actualism

Using the actual processes operating on Earth today to interpret the past; not inventing unrecognized processes to explain the past. Concept basically the same as uniformitarianism; don't use supernatural causes to explain away problems.

Magnetism

A group of physical phenomena associated with moving electricity.

Ridge

A volcanic mountain range that lies along the spreading centers on the floors of the oceans.

The layered Earth (physical composition)

AHLAMOI. Atmosphere (gas), hydrosphere (liquid), lithosphere (solid), asthenosphere ("soft plastic"), mesosphere ("stiff plastic"), outer core (liquid), inner core (solid). See diagram on p. 26 for labels.

Divergent boundaries

Aka constructive boundaries. Continental rifts and "mid-ocean" ridges--hot mantle material wells up, pulls it apart. Decompression melting.

Materials

Gas and liquids are both fluids, but a gas is capable of indefinite expansion, while a liquid is a substance that flows readily and has a definite volume but no definite shape. A solid is firm, offers resistance to pressure and doesn't easily change shape.

Tidal friction

Gravitational attraction between Earth, Moon, and Sun stretches the solid mass of the Earth and converts some energy from Earth's rotation into heat.

Lateral spreading aided by?

Gravity, buoyancy, and convection. Gravity pulls material downward and outward (spreading). The lateral spreading is aided by the push of positive buoyancy at spreading ridges and may be aided by convection cells of mantle heat, which rise and move laterally beneath the lithosphere before descending.

Characteristics of divergent-boundary EQs: Mid-Atlantic Ridge

Lots of EQs. All VERY shallow. Almost all weak. Bc lithosphere is new, hot, thin, ductile, weak.

Subduction-zone EQ characteristics

Lots of EQs. All depths. Weak to strongest. Bc lithosphere is old, cold, thick, brittle, strong.

Transform fault EQ characteristics

Lots of EQs. All shallow. Weak to strong. Bc lithosphere is mature, but "normal" thermally--lower crust is hot & ductile. Little to no volcanism.

Increasing temp & pressure into the Earth result in?

Physical (mechanical) layering. Increasing temp melts stuff, increasing pressure keeps stuff solid. Both increase -- sometimes pressure wins, sometimes temp wins. Different layers/materials have different melting temps.

Plate interiors

Plate interiors are relatively quiescent, but there are some earthquakes and volcanoes in plate interiors.

Single greatest aggravating circumstance for disasters:

Poverty.

Grand Unifying Theory

Pretty much everything covered above. How plate-tectonic action happens.

Solar radiation

Sunshine. Energy emitted from the Sun mostly in infrared, visible light, and ultraviolet wavelengths.

The recycling of the upper few 100 km of Earth is called?

Tectonic cycle. New lithosphere forms at oceanic volcanic ridges, the lithospheric plates spread apart to open ocean basins, and then the oceanic plates are reabsorbed into the mantle at subduction zones. Has been adapted by geologists as the term tectonics, which describes the building of topography and the deformation and movement within the Earth's outer layers.

Plastic

The behavior of a material that flows as a fluid (liquid) over time, but is strong (solid) at a moment in time. Mantle is plastic

Atmosphere

The gaseous envelope around Earth, composed chiefly of nitrogen and oxygen.

Key concepts 06--plate tectonics

The lithosphere--the stony, hard, brittle outer shell of the Earth--is the "thermal boundary layer" between the hot interior of the Earth and the cold of space. The lithosphere is divided into thin, areally large plates. The plates move, driven by convection. Interactions at plate boundaries are responsible for much of the geologic activity at the Earth's surface--and the hazards!

Mesosphere

The mantle from the base of the asthenosphere to the top of the core.

Continental drift

The movement of continents across the face of the Earth, including their splitting apart and recombining into new continents. Changes of Pangaea include deformation during the process of rifting, growth of river deltas, volcanoes, coral reef masses, erosion of the continents, and land movements.

Epicenter

The point on the surface of the Earth directly above a fault movement (ie, earthquake location). Depths of epicenters increase toward continents. Can connect the dots of these epicenters to outline the edges of the tectonic plates.

The flow of energy from Earth's interior to its surface comes mainly from what sources?

1. Impact energy, 2. Gravitational energy, 3. Ongoing decay of radioactive isotopes (also additional energy from tidal friction)

Convergent boundaries

Aka destructive boundaries. Subduction zones and collisional mountain belts. Continent-continent collision (mountain-building).

Where do earthquakes at depth commonly occur?

Along inclined planes adjacent to deep-ocean trenches.

Plumes

An arm of magma rising upward from the mantle.

To summarize, where does evidence for plate tectonics come from?

Ancient magnetic fields; ages of rocks, sediments, and fossils, as well as the depth of water, all increase away from the oceanic ridges.

Earth history

As Earth was formed, the gravitational force may have pulled more metallic pieces toward the center. Iron has a higher melting point, so liquid iron was pulled in. This released a lot of gravitation energy that converted to heat, which produced widespread melting and likely caused low-density materials to rise and form: 1. a crust of low-density rocks at the surface of the Earth, 2. large oceans, 3. a denser atmosphere.

Subduction-zone volcanism process

As plate moves across ocean basin, sediment gets left upon it. At depth, the oceanic crust undergoes weathering, rocks become minerals that absorb water. Volatiles get through subducting plate, go into mantle, lower the melting temp of the rocks (at convergent boundaries, undergoes flux melting), flux melting forms magma, magma goes into surface.

Distinctions in plate-boundary types

Each plate-boundary type has distinctive processes and patterns of seismicity (earthquakes) and volcanism

As a result of differentiation...

Earth is chemically (compositionally) layered. Dense stuff sinks, as a result we get iron in the core, then iron silicates in the mantle and crust.

Different deformations stress can produce

Elastic (recoverable) deformation, eg bending an eraser that returns to original form. Ductile (plastic) deformation, eg squishing Play-Doh and the change is permanent. Or brittle deformation, when it fractures, eg shattering ice.

Energy flow leads to...

Energy flow--disturbances (fluctuations)--hazards--disasters.

Radioactive isotopes

Energy is released from radioactive isotopes as they decay. There's a declining output of radioactive heat inside the Earth, so the flow of energy from Earth's interior is on a slow decline heading toward zero.

Plate tectonics & volcanoes

Explains global volcanism. Most volcanoes are on the divergent plate boundaries.

When are volcanoes formed

If an oceanic plate goes beneath another oceanic plate at a convergent plate boundary, an island arc of volcanoes next to a trench can form. If the subducting oceanic plate is pulled beneath a continent-carrying plate, the top of the down-bending oceanic plate forms a trench, and a line of active volcanoes builds on the continent edge.

Impact energy & gravitational energy

Impact energy of masses colliding w the growing Earth produced heat. Gravitational energy was released as Earth first pulled into an increasingly dense mass. This energy converted to heat. All this heat during the formation of the Earth didn't readily escape bc rock conducts heat v slowly. Some of this early heat is still flowing to the surface today.

Theory of the Moon's origin

Impact of Earth w another body, the resultant dust and vapor condensed to form the Moon. Suggests that the Moon is made mostly from Earth's rocky mantle.

Breakdown the lithosphere

Broken into thin, areally large pieces called plates. The study of the movements and interactions of the plates is known as plate tectonics. The plates pull apart during seafloor spreading at divergence zones, slide past at transform faults, or collide at convergence zones. These plate-edge interactions are directly responsible for most earthquakes, volcanic eruptions, and mountains on Earth.

Key parts of a hazard

Recognition (what's the hazard?), avoidance (stay away from the hazard!), mitigation (minimize/recover from the disaster).

Yield stress

The stress difference at which permanent deformation first occurs.

Rift

The valley created at a pull-apart zone. Term commonly describes the valley that occurs along the axis of volcanic mountain ranges of seafloor spreading centers.

Hydrosphere

The waters of the Earth, including the oceans, lakes, and rivers.

Convergence zone

A linear area where plates collide and move closer together. This is a zone of earthquakes, volcanoes, mountain ranges, and deep-ocean trenches.

Divergence zone

A linear zone formed where plates pull apart, as at a spreading center.

Hot spots

A place on Earth where a plume of magma has risen upward from the mantle and through a plate to reach the surface. Produce more heat, causing hotter rocks w lower density. These masses of buoyant hot rock rise upward as plumes through the mantle, begin to melt near the top of the overlying asthenosphere, and pass up through the lithosphere as magma. Hot spots have active volcanoes above them on Earth's surface. When moving plates carry volcanoes away from their hot-spot source, they become extinct.

Magnetic field

A region where magnetic forces affect any magnetized bodies or electric currents. Earth is surrounded by a magnetic field.

Magnetization patterns on the seafloors

A relationship exists between the time of reversals of magnetic polarity (as dated from a sequence of solidified lava flows) and the widths of alternately polarized seafloor.

Transform fault

A strike-slip fault that connects the ends of two offset segments of plate edges, such as spreading centers or subduction zones.

Pangaea

A supercontinent that existed during Late Paleozoic time when all the continents were unified into a single landmass. Idea based on continental drift. Hypothesis only accepted when scientists realized that the lithosphere decouples from the asthenosphere and moves laterally, and that the relatively small, low-density continents, set w/in the oceanic crust, could be carried along as incidental passengers.

Nuclear fusion

Combining smaller atoms to make larger atoms, with a resultant release of energy.

How the heat moves through different layers

Conduction in inner core bc metal. Outer core is convection. Mesosphere is some convection (slow), some conducting. Asthenosphere is convection (what drives plate tectonics).

Transform faults

Conservative boundaries. Also on continents.

The plates movement is driven by what?

Convection in the asthenosphere

The layered Earth (chemical composition)

Core (metallic), mantle (heavy rock), crust (low-density rock). Densest material pulled toward the center. Least dense substances escaped to the surface. The entire core is rich in iron. Surrounding the core is the rocky mantle. Then, oceans and atmosphere. Both temp and pressure inc continuously from Earth's surface to the core.

Strike-slip fault

Fault where most of the movement is horizontal or slide-past in character

Complexities in the magnetic field

Fluctuates with regions of turbulence in the flow of fluid iron in the outer core. The magnetic field exists to protect Earth from much of the incoming solar and space radiation. The change in orientation of the magnetic field leaves its imprint in rocks.

Hypocenter

Focus of the earthquake, the point below where the earthquake happens. Earthquakes really occur at hypocenters. Hypocenters are on the subducting plate.

Radioactive-decay process is measured by what

Half-life, the length of time needed for half the present # of atoms of a radioactive isotope (parent) to disintegrate to a decay (daughter) product.

Hotspots

Have mantle plumes. As the plate moves, the hot spot is fixed in mantle, so volcanoes keep being formed as the older ones become inactive. Think Hawaiian islands. Some hotspots lie on ridges (Iceland).

Mantle

Largest zone of the Earth. Comprises 83% of Earth's volume and 67% of its mass.

Lava flow

Lava flows pile up as sequences of stratified (layered) rock, and the magnetic polarity of each rock layer can be measured. Many of the volcanic rocks contain minerals w radioactive isotopes that allow us to determine the age of the volcanic rock, or how long ago the lava solidified.

Crust & lithosphere IMPORTANT DISTINCTION THAT WILL BE ON THE EXAM

Lithosphere = crust PLUS uppermost mantle. INCLUDES THE CRUST.

Ocean mountain ranges and deep trenches

Long and continuous mountain ranges are seen to form at spreading centers where plates pull apart and magma rises to fill the gaps.

Mid-Atlantic Ridge

Lots of shallow, weak earthquakes.

Paleomagnetic time-scale

Magma is injected into the oceanic ridges where it is imprinted by Earth's magnetic field as it cools to form new rock. Then the seafloor/ocean crust/lithosphere is physically pulled away from the oceanic ridges as if they were parts of two large conveyor belts going in opposite directions.

Lava

Magma that flows on the Earth's surface. As the lava cools, minerals begin to grow as crystals. When lava cools below the Curie point, the lava becomes a magnetic field.

Origin of the Sun and planets

Matter collided within a rotating cloud of gas and dust. As central mass grew larger, temp increased, and the process of nuclear fusion began. On Earth, we feel the energy results of nuclear fusion as solar radiation.

Simplify the tectonic cycle

Melted asthenosphere flows upward as magma and cools to form new ocean floor/lithosphere. New lithosphere slowly moves laterally away from the zones of oceanic crust formation on top of the underlying asthenosphere (aka seafloor spreading). When the leading edge of a moving slab of oceanic lithosphere collides w another slab, the older, colder, denser slab turns downward and is pulled by gravity back into the asthenosphere (subduction, weak plastic convects), while the less-dense, more buoyant slab overrides it. Finally, the slab pulled into the mantle is reabsorbed.

Key concepts 07--plate boundaries

Most of the "action" of plate tectonics (EQs, volcanoes, mountain-building, basin formation) takes place at plate boundaries. Plate interiors are relatively quiescent, but there are some EQs and volcanoes in plate interiors. Each plate-boundary type has distinctive processes and patterns of seismicity (EQs) and volcanoes.

Motion of plates measured in?

Motions are in cm/yr (full spreading rate).

Systematic increases in seafloor depth (age)

Moving away from the oceanic ridges, ocean water depths increase systematically with seafloor age. This is due to the cooling and contraction of the oceanic crust w a resultant increase in density.

Ocean basins

Much younger than the Earth, bc the ocean basins are young features that are continuously being formed and destroyed. Along the oceanic ridges, volcanism is active, and new seafloor/oceanic crust is forming. Moving away from oceanic ridges, the seafloor volcanic rocks and islands become progressively older. Also, the older the seafloor, the more time it has had to accumulate a thick cover of sand, silt, clay, and fossils.

Conservative boundary process (continental as well as oceanic)

One lithospheric plate slides past another. No hot material rises or cold material sinks. No heating or refrigeration. Plates are neither created nor destroyed. Also frictional.

Key concepts 08--Mid-plate EQs and volcanoes

Some EQs and volcanoes are in plate interiors (New Madrid, Yellowstone). Mid-plate EQs prob happen mostly on old "fossil" faults, building up stress in modern plate-tectonic stress system; triggers unknown. Mid-plate volcanism related to mantle plumes, columnar upwellings of hot asthenosphere material--ultimate source may be core mantle boundary.

Core

The central zone or nucleus of Earth. Made mostly of iron and nickel. Exists as a solid inner zone surrounded by a liquid outer shell. Inner core is a solid mass, extremely hot. Outer core is mostly liquid, and the viscous movements of convection currents within it are responsible for the generation of Earth's magnetic field. Earth's magnetic field originates within the core.

Uniformitarianism

The concept that the same laws and processes operating on and within Earth throughout geologic time are the same laws and processes operating today. Study the present to understand the past and then make probabilistic forecasts about the future.

Isostasy

The condition of flotational equilibrium wherein the Earth's crust floats upward or downward as loads are removed or added. Applies a principle of buoyancy to explain how the low-density continents and mountain ranges literally float on the denser mantle below. Movements up and down, v movements horizontally (plate tectonics)

Trenches

The elongate and narrow troughhs where ocean water can be more than twice as deep as usual. Trenches mark the down-going edges of subducting plates reentering the mantle.

Asthenosphere

The layer of the Earth below the lithosphere in which isostatic adjustments take place. The rocks here deform readily and flow slowly.

Origin of magnetism

The origin of Earth's magnetic field involves movements of the iron-rich fluid in the outer core, which generate electric currents that in turn create the magnetic field. Fluid iron is an excellent conductor of electricity. The molten iron flowing around the solid inner core is a self-perpetuating dynamo deriving its energy both from the rotation of the Earth and from the convection of heat released by the crystallization of minerals at the boundary of the inner and outer cores.

Buoyancy

The quality of being able to float, usually on water or rock.

Topography

The shape of Earth's surface both above and below sea level.

Spreading centers

The site where plates pull apart and magma flows upward to fill the gap and then solidifies as new lithosphere/ocean floor

Lithosphere

The stony, hard, brittle, rigid outer shell of the Earth. "Thermal boundary layer" between the hot interior of the Earth and the cold of space. Sometimes bends, sometimes breaks.

What happens when subduction stops?

Volcanism ceases--quickly. EQs continue, but largest become rarer.

Behavior of materials

When materials are subjected to sufficient stress (force) they deform or undergo strain (change) in different ways.

Seafloor spreading

Where tectonic plates pull apart, magma wells up and solidifies to create volcanic mountains, which in turn are pulled apart as new ocean floor.