Chapter 29 Vocabulary
In your own words, rewrite each definition and draw a picture to represent the idea or definition.
29.1: Fossils - Key Idea: Fossils form in several ways.
Fossil: The remains, impression, or any other evidence of life from another geologic age preserved in
rock.
Paleontology: The study of life that existed in prehistoric times
Mold: A hollow depression in rock formed when a fossil dissolves out of the rock; shows the original
shape and surface of the fossil.
Cast: An object created when minerals seep into and fill a mold, forming a copy of the original fossil.
Trace Fossil: Any indirect evidence of life preserved as an impression in rock; trails, footprints, tracks,
burrows, and bite marks.
29.2 Relative Time
Key Idea: Scientists use a number of principles and methods to determine the order of past geologic
events.
Relative Dating: The process of placing events in the sequence in which they occurred; does not identify
actual dates.
Strata: The layers of sedimentary rock that form after particles settle out of a fluid and are compressed
over time.
Unconformity: The layer or layers of rock missing from a strata sequence.
Correlation: The matching of rock layers from one area with those of another area.
Index Fossils: The fossilized remains of organisms that lived and died within a particular time segment of
Earth’s history and that can be used to correlate rock layers.
Key Bed: A single, widespread rock layer that is unique and easily recognizable; used to correlate rock
layers.
29.3 Absolute Time
Key Idea: Scientists use radioactive-dating methods to measure absolute time.
Absolute Time: The method of recording events that identifies the actual date of an event, such as when
a rock formed.
Radioactive decay: The process by which radioactive isotopes emit or capture tiny particles; includes
alpha decay, beta decay and electron capture.
Parent isotope: The original element that will, after radioactive decay, become an isotope of a different
element with a different atomic number.
Daughter isotope: An element that is the product of radioactive decay.
Half-life: The time it takes for half the atoms in a sample of a radioactive element to decay to a stable
end product.
Radiometric dating: A technique used to measure absolute time in which the amounts of a parent and
daughter isotope within a rock or mineral are measured and the ratio used to find the age of a rock.