Chapter 8 Flashcards
Age of the Earth
prior to 19th century age of Earth was based on religious beliefs: bible says approximately 6000 years, and Chinese and Hindu beliefs say its old beyond comprehension
James Hutton
“father of geology,” realized geologic processes require vast amounts of time
Charles Lyell
popularized Hutton’s concepts in book Principles of Geology
Relative Age
the order of events or objects from oldest to youngest: original horizonality, superposition, lateral continuity,
cross-cutting relationships, inclusions, uncomformities, and correlation
Numerical Age
the age of events or objects expressed as a number or numbers: determined using radiometric dating
Radiometric Dating
determining how much radioactive decay of a specific element has occurred since a rock formed or an event occurred
Contacts
surfaces separating successive rock layers (beds)
Formations
bodies of rock of considerable thickness with recognizable characteristics allowing them to be distinguished from adjacent rock layers
Original Horizonality
beds of sediment deposited in water are initially formed as horizontal or nearly horizontal layers
Superposition
within an undisturbed sequence of sedimentary or volcanic rocks, layers get younger from bottom to top
Lateral Continuity
original horizontal layer extends laterally until it tapers or thins at its edges
Cross Cutting Relationships
a disrupted pattern is older than the cause of the disruption: intrusions and faults are younger than the rocks they cut through
Baked Contacts
contacts between igneous intrusions and surrounding rocks, where surrounding rocks have experienced contact metamorphism
Inclusions
fragments embedded in host rock are older than the host rock
Uncomformity
a surface (or contact) that represents a gap in the geologic record
Disconformity
an unconformity in which the contact representing missing rock layers separates beds that are parallel to each other
Angular Uncomformity
an unconformity in which the contact separates overlying younger layers from eroded tilted or folder layers
Nonconformity
an unconformity in which an erosional surface on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rock: plutonic and metamorphic rocks exposed by large amounts of erosion, and it typically represents a large gap in the geologic record
Correlation
The determination of the time-equivalency of rock units, matching of rocks of similar ages in different regions
Physical Continuity
physically tracing a continuous exposure of a rock unit
Similarity of Rock Types
assumes similar sequences of rocks formed at same time, and can be inaccurate if very common rock types are involved
Correlation by Fossils
fossil species succeed one another through the layers in a predictable order
Fossils
Evidence of past life, traces or remains of prehistoric life now preserved in rock. They are generally found in sediment or sedimentary rock (rarely in metamorphic and never in igneous rock)
Paleontology
study of fossils