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-Once withdrawn, the rock and soil sink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
-Method of measuring the age of an object/event in years by analyzing isotopes of remaining radioactive elements
II. Absolute Dating
-Unstable isotopes that decay into other forms to achieve stability
Proton + = Same
Neutron O = Diff (mass)
-Parents Isotopes (Unstable) - Radioactive
-Daughter Isotopes (Stable)
Radioactive Isotopes
Parent Isotopes = ?
Parent Isotopes = (Unstable) - Radioactive
-Time needed for half of a substance sample to undergo radioactive decay
-In every half-life, the amount of parent material decreases by half
-Ex. Sample isotope with a ——– of 10,000 years
Half-Life
Daughter Isotopes = ?
Daughter Isotopes = (Stable)
-In which an unstable parent nucleus emits two protons and two neutrons
Alpha Decay
-In which an electron is emitted from a neutron in the nucleus
Beta Decay
-In which a proton captures an electron and is thereby converted to a neutron
Electron Capture
-Determining the absolute age of a sample based on the ratio of the parent material to daughter material
-Ratio of parent to daughter
Radiometric Dating
What is the formula of radiometric dating
Age = 3.322log((p + d)/p)
RELATIVE DATING AND ABSOLUTE DATING
DIFF AND SIM
RELATIVE
-Determines the order of formation of remains using stratigraphic methods
-Qualitative method of dating (Characteristics)
ABSOLUTE
-Determines the age of remains using radiometric methods
-Quantitative method of dating (Numbers AKA Isotopes)
SAME
-Provides the order of formation of remains
-Provides the age of remains
-System of chronological measurement
-Relates stratigraphy and time to any geologic events
Geologic Time Scale
(Millions of years)
Age
(Tens of millions of years)
Epoch
(100 million years)
Period
(Several hundred million years)
Era
(Half a billion years or more)
Eon
-Remnant of any ancient animal or plant that has been preserved in rocks
Fossils
-Age of fossil = Age of rock on which it is found?
True
-Hard parts which favor fossilization
-At least lived for a short period of time
-Before it evolved into a different creature
-Good distribution and lived all over the world
-Features characteristics found in a particular geologic event
Index Fossils
