Geologic Terms

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Orogeny

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42 Terms

1

Orogeny

Period of mountain building in which tectonic forces cause rocks to be faulted, folded and/or metamorphosed

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2

Shield

Ancient cores of continents made of Precambrian igneous & metamorphic rocks

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3

Mold

Empty cavity formed when the hard parts of a buried organism are dissolved/reacted away

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4

Trace Fossil

Indirect evidence for ancient life such as footprints, trails or burrows

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5

Dendrochronology

Study of tree rings to calculate dates of past events and to determine climatic changes in the past

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6

Varves

Alternating bands of light- and dark-colored sediments deposited respectively during summer and winter in large lakes

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7

Paleozoic

Era of "Ancient Life"

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8

Mesozoic

Era of "Middle Life"

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9

Cenozoic

Era of "Recent Life"

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10

Phanerozoic

Eon of "Visible Life"; Eon of multicellular organisms with hard parts

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11

Proterozoic

Eon of one-celled organisms

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12

Archean

Eon of "Ancient" Time

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13

Hadean

Eon of "Hellish" Time

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14

Geologic Time Scale

Chart used to describe earth's history by dividing it into various eons, eras, periods & epochs, originally based only on the fossil record

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15

Cast

A 3-D copy of the hard parts of an organism formed when the hard parts of a buried organism are dissolved/reacted away and the resulting cavity is filled with sediments

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16

Stromatolites

The most common Precambrian fossils (of algae) found in numerous places around the world and dating back hundreds of millions to billions of years

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17

Mass extinction

When many types of living things (species) disappear from earth at the same time

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18

Evolution

Change in living things through time

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19

Paleontologist

Scientist that studies fossils and ancient organisms

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20

Petrified

Turned to stone; fossilized in rock

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21

Principle of Superposition

In undisturbed sedimentary rocks, the oldest rocks are on the bottom and the youngest are on the top

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22

Principle of Cross-Cutting Relationships

Younger features cut across or through older features

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23

Principle of Contact Metamorphism

Rocks metamorphosed by the magma are older than the intrusion or lava flow, unmetamorphosed rocks are younger than the lava flow

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24

Principle of Fossil Succession

Fossils and the rocks they are found in can be arranged in a definite order according to their age

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25

Principle of Original Horizontality

Sediments are deposited in originally flat layers

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26

Daughter Isotope

Isotope formed from the decay of an unstable isotope

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27

Uniformitarianism

Fundamental principle of geology that states the processes which occur on Earth today are the same processes that occurred in the past; the present is the key to the past

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28

Correlation

Matching a rock layer or rock unit in one place with the same rock layer in another place using rock type, thickness, fossils, etc.

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29

Unconformity

Any break in the rock record when erosion took place instead of deposition

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30

Relative Date

The age of a rock formation or event compared to the surrounding rock formations or events

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31

Fossils

Remains or traces of ancient life

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32

Index Fossils

Fossils that are widespread over a large area of earth and only existed for a short amount of time and are used to give approximate numerical dates to rock formations and geologic events

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33

Radiometric Date

The absolute age of a rock or mineral calculated using the ratios of parent and daughter isotopes

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34

Absolute Date

Date that gives the number of years that have passed since a rock formed or an event occurred

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35

Radioactive Decay

The spontaneous breaking apart of nuclei of atoms through time to form new & different atoms

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36

Parent Isotope

An unstable isotope that has not yet decayed

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37

Half life

The time it takes half the atoms of a parent isotope to decay into atoms of the daughter isotope

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38

Isotope

Atoms that have the same number of protons, but different numbers of neutrons

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39

Eon

The largest time expanse in geologic time consisting of 100s of millions of years

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40

Epoch

The smallest time expanse in geologic time consisting of millions of years

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41

Era

The second largest time expanse in geologic time consisting of many tens of millions of years

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42

Period

The second smallest time expanse in geologic time consisting of tens of millions of years

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