Earth Lecture 2 + 3

Relative Dating 

Determining the order in which rock layers formed relative to the layer around them 

Absolute Dating

Determining an absolute (Number) age for a rock unit

Principle of Original Horizontally

All rocks were originally sediment and were deposited horizontally

Principle of Superposition

Each layer has its own history. Oldest at bottom, youngest at top

Principle of lateral continuity 

Sediment extends laterally in all directions until it thins or terminates against basin edge 

Deep time 

Materials furnished from the ruins of former continents. Rock cycle, long timescale 

Uniformitarianism

Assumes that the some laws and processes we observe today apply to the past

Principle of cross-cutting relationship

Igneous intrusions of fault are younger than the rocks they intrude of displace

Unconformities

Breaks in the rock record where there is time missing between laters. Three types: Disconformity , angular unconformity, and nonconformity 

Angular 

Rocks at an angle beneath horizontal 

Nonconformity

Non sedimentary beneath sedimentary

Disconformity

Dislike because tricky to identify sedimentary beneath sedimentary, time missing

Principle of inclusions

when one rock constraints pieces of inclusions of other rocks, the included rock is older than the host rock 

Principle of fauna/fossil succession

fossils can be used to correlate rocks of the same age across a wide geographic range 

Isotopic or radiometric dating

Uses the principles of radioactive decay to determine how many times the parent isotope has decayed into the daughter isotope

Varve dating

Using lakes of deposits

Weathering 

Process that turns rock into sediment 

Mechanical Weathering

Pressure expansion, frost wedging, root wedging, salt expansion

Chemical Weathering

Carbon acid, hydrolysis, dissolution, oxidation

Erosion

Taken that sediment and moving it away. Usally driven by wind, water, gravity, or ice

Erosional feature 

Over time erosion can create feature such as hoodoos, alcoves, windows, and arches 

Making Hoodoos

Combinations of first wedging and chemical dissolution

Cliff dwelling

Long house was excavated and stabilized