Pearson Prentice Hall Chapter 12 Vocabulary
Terms in this set (18)
The physical, chemical, and biological laws that operate today have also operated in the geologic past; they have been at work for a very long time.
(12.1) Relative Dating
Identifying which rock units formed first, second, third, and so on; the sequence in which they occurred, but not how long ago they occurred.
(12.1) Law of Superposition
In an undeformed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below it.
(12.1) Principle of Original Horizontality
The layers of sediment are generally deposited in a horizontal position.
(12.1) Principle of Cross-Cutting Relationships
When a fault cuts through rock layers, or when magma intrudes other rocks and crystalizes, we can assume that the fault or intrusion is younger than the rocks affected.
A long period during which deposition stopped, erosion removed previously formed rocks, and then deposition resumed.
Matching up rocks of similar age in different regions to develop a geologic time scale that can be applied to the entire Earth.
The remains or traces of prehistoric life; important components of sediment and sedimentary rocks.
(12.2) Index Fossil
Fossils that are widespread geographically, limited to a short span of geologic time, and occur in large numbers.
The process in which nuclei are unstable and spontaneously break apart or decay.
The amount of time necessary for one half of the nuclei in a sample to decay to its stable isotope; a common way of expressing the rate of radioactive decay.
(12.3) Radiometric Dating
The procedure of calculating the ages of rocks and minerals that contain radioactive isotopes.
(12.3) Radiocarbon Dating
A method in which carbon-14 is used to date recent events.
(12.4) Geologic Time Scale
A collection of units that represent specific amounts of time, all from Earth's 4.56 billion year history.
The greatest expanses of time; for example, Phanerozoic Eon which began about 540 million years ago.
A subdivision of an Eon.
A subdivision of an Era
A subdivision of a Period
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