Earth Science: History of the Earth Flashcards
-Puts geologic events into chronological order
-The rocks left behind are put into a sequence
-The method of reading the order is called stratigraphy
-How old something is in relation to other objects, cannot provide a specific date
I. Relative Dating
Two kind of relative dating
- Laws of Stratigraphy
- Unconformities
-From deposits of pre-existing rocks of once-living organism
-Buried underground
-Include sandstone, limestone, and shale
-Sediments carried in rivers and deposited in lakes and oceans
-Once buried, the sediments lose water and become cemented to form rock
Sedimentary Rocks
-Stacked-up layers of sedimentary rock
Strata
-Sinking of the ground because of underground material movement
-Ground water holds up the soil
-Once withdrawn, the rock and soil sink
Subsidence
-“The laws of nature are constant but the rates and intensities of change have varied through time”
-Constant change
-Some changes are faster and some slower
Actualism (Modern Uniformatism)
-The patterns in which rock layers are deposited
-The order
- Laws of Stratigraphy
-Estimate whether an object is younger or older than other things found
-Does not offer specific dates
Relative Dating Methods
-Subatomic particle with a positive electrical charge
-Found in atomic nucleus of every element
Protons
-Subatomic particle with a neutral electrical charge or uncharged
-Only hydrogen lacks a neutron
-Found in atomic nucleus of every element
Neutrons
-Subatomic particle with a negative electrical charge
-Can be either bound or free to an atom
-Found in atomic nucleus of every element
Electrons
-First to realize that the Earth’s crust contains a chronological history of geologic events
-History of the earth could be deciphered by study of fossils and strata
Nicolas Steno (1638-1686)
-Oldest Layer = bottom
-Youngest Layer = on top
Principle of Superposition
-Sedimentary rocks always form in horizontal layers
-Stacked on top of each other horizontally
Principle of Original Horizontality
-Rock layers are continuous unless encountered by deposition
-Layers are on the same level but a piece is taken out
Principle of Lateral Continuity
-Rocks that cut across is younger than those it cut across
-A younger rock that cuts old rocks
Principle of Cross-cutting Relationships
-Discovered that different stratified formations in England contain distinctive assemblages/collection of fossils
-Kinds of fossils are unique to a particular layer
-Added two more to the relative dating methods
William Smith (1769 – 1839)
-Any rock fragments that are included in a rock must be older than the rock in which they are included
-Rock A – Older
-Rock B - Younger
Law of Inclusion / Principle of Inclusions
-Assemblages of fossil contained in strata are unique to the time they lived
-Can be used to correlate rocks of the same age
-Despite being spread around the world
-Despite wide geographic distribution
Law of Fossil Succession
-A surface within several layers of sediment where there is a missing sedimentary layer
-Contact between sedimentary rocks that are significantly different in age
-Boundary between rock, caused by period of erosion or pause in sediment accumulation
-Rock layers that were eroded forming a gap in the layer sequence
-Break in time in a continuous rock record
Unconformities
-Sedimentary rocks form, then tilted and eroded
-New sedimentary rocks are laid on top
Angular Unconformity
-Nonsedimentary rocks (From solidified magma)
-Line between sedimentary and nonsedimentary rocks
Nonconformity
-Sedimentary rocks form, then eroded
-New sedimentary rocks are laid on top
Disconformity
-Strata are parallel to each other
-The contact is simple bedding plane indicative of a continuous deposition
-Little or no evidence of erosion
-Difficult to detect
Paraconformity
