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Geologic time scale

Earth Science

QuestionAnswer
Eon measured in billions of years, is the longest time unit of the geologic time scale
Era defined by the differences in life-forms found in rock and measured in hundreds of millions to billions of years, is the second-longest span of time on the geologic time scale
Period measured in tens of millions of years before present. are defined by the life-forms that were abundant or became extinct during the time in which specific rocks were deposited
Epochs smaller divisions of geologic time and are usually measured in millions of years to tens of millions of years
Relative dating estimating the dates of rocks and fossils according to the other rocks and fossils around it
Absolute dating Determining the age of rocks and fossils by doing tests to get the exact age
Uniformitarianism states that processes that have been occurring today such as weathering and mountain building have been occurring since the Earth formed
Methods for relative dating: 1.Law of Superposition 2.Cross-cutting relationships 3.Unconformity 4.Correlation
Law of Superposition In a rock sequence, the oldest rocks are located at the bottom and the youngest are at the top
Cross-cutting relationships states that an intrusion or a fault is younger than the rock it cuts across
Unconformity is a gap in the rock record usually caused by an erosional surface becoming buried by the deposition of younger rocks
Correlation the matching of outcrops of one geographic region to another
Absolute dating methods 1.Radioactive Decay 2.Radiometric Dating 3.Half-life 4.Tree Rings 5.Seasonal Climatic Changes 6.Distinctive Sediment Layers
Fossils Evidence of once living material
Altered hard parts When the Hard parts of an organism have been removed and replaced with minerals
Molds the impression that organisms leave in rocks
Casts when molds are filled in with minerals
Index fossil the remains of a plant or animal that can be used to correlate rock layers or to date particular rock layers
Trace fossils Indirect evidence of plant and animal life
Created by: elarocco
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