Geologic Time and Change

Endogenic systems involve internal processes – Tectonics, Earthquakes, Volcanoes.

Flows of heat and material are deep below the surface, with radioactive decay being the main energy source.

Exogenic systems involve external processes – Weathering, Erosion, Rivers, Oceans, Glaciers.

Powered by solar energy & gravity

Absolute vs. Relative timescale:

Relative – Sediment at the top is younger than the sediment at the bottom (Stratigraphy)

Absolute – uses radioactive decay of isotopes to find the exact age

Uniformitarianism – physical processes operating today operated in the past

Catastrophism – Compressed timescale for Earth’s existence

Punctuated Equilibrium – Periods of stability interrupted by dramatic changes

We are in the Cenozoic and Quaternary.

Core:

Inner Core – solid iron

Outer Core – Molten Iron

Mantle:

Guttenberg discontinuity – Line in between Mantle and core

80% of Earth’s surface

Lithosphere: Rocky, rigid layer made up of crust and upper mantle

Asthenosphere: is a plastic layer below the crust; drives plate tectonics

Minerals are a natural compound having a specific chemical formula and crystalline structure.

Rocks are a bunch of minerals cemented together.

Igneous (was molten)

Sedimentary (from sediment)

Metamorphic (changed by heat/pressure)

Silicates: common mineral family (quartz, feldspar, gemstones)

Oxides: Oxygen + other metal (iron oxide, calcium oxide)

Carbonate: Carbon + Oxygen + Metals (Calcite: CaCO3)

Igneous: forms from magma found below the earth’s surface.

Intrusive – forms within the earth’s crust. Cools slowly. (granite)

Extrusive – molten material above the earth’s surface. Cools quickly. (lava/basalt)

Sedimentary: Rocks formed from sediment

Existing rock -> weathering; erosion; deposited and buried

Fragments of other rocks -> transport by water

Sandstone (sand), Shale (mudstone), Limestone (CaCO3), Coal (plants)

Metamorphic: Rocks put under intense heat and/or pressure, altering the chemical composition

Regional metamorphism – sediment collecting in broad depression

Contact metamorphism – heating due to rising magma

Foliated = wavy striations, non-foliated = homogenous

Shale (clay) -> Slate, Granite -> Gneiss; Basalt -> Schist; Limestone -> Marble; Sandstone -> Quartzite.

Hydrologic cycle – erosion, transportation, deposition

Rock cycle – 3 basic rock types

Tectonic cycle – moves material between the surface and mantle

Continental crusts light, ocean floor dense

Shapes of continents, geology, fossils suggest close past proximity

Geodetic measurements in Greenland indicated movement

sea floor spreading: undersea mountain ranges

mid-ocean ridges: upwelling magma: crust fractures, spreads and cools

magnetic reversals – particles align themselves with prevailing magnetic field

youngest crust: spreading center; oldest oceanic crust at subduction zones (208 mya)

Relief – Vertical elevation differences in the landscape | Topography – Describes earths surface

Crustal orders of Relief:

1st order: Huge continental platforms/ocean basins

2nd order: Mountain masses, plains, lowlands

3rd order: Individual mountains, valleys and cliffs.

Hypsometry – distribution of Earth’s surface and elevation in relation to sea level

Earth’s Topographic Regions: Plains (ie: Great Plains), High Tablelands (ie: Colorado Plateau), Hills/Low Tablelands (ie: Appalachians), Mountains (ie: Sierra Nevada), Widely Spaced Mountains (ie: Great Basin Mountains), & Depressions (ie: Snake River)

Crustal Formation:

Residual Mountains and stable continental cratons, formed from inactive remnants of ancient tectonic activity

Tectonic Mountains and landforms, produced by folding, faulting, and crustal movements

Volcanic features, formed by surface accumulation of molten rock from eruptions of subsurface materials

Rocks are subjected to stress due to tectonic forces, gravity, and pressure from overlying rocks.

Three types of stress: Tension, compression, and shear

Strain is how rocks respond to stress à expressed in rocks folding or faulting

Anticline – ridge of a fold, slope downward away from axis

Syncline – trough of a fold, slope downward towards the axis (trough)

Thrust fault – overturned folds

Warping – greater in extent; ie: isostatic rebound (Canada)

Faulting: when the stress is so great, the crust breaks

Normal Fault – Pulling rocks apart (tension fault)

Reverse Fault – Compression pushing against rocks (thrust fault), one part of crust overruns the other

Strike-Slip Fault – Stress applied is in a shearing direction and you get a break.