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
Geologic Importance of Fossils
They aid in interpretation of the geologic past, serve as important time indicators, and allow for correlation of rocks from different places
William Smith
noted that sedimentary strata in widely separated area could be identified and correlated by their distinctive fossil content
Fossil Succession
fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content
Index Fossil
geographically widespread fossil that is limited to a short span of geologic time
Geologic Time Scale
It is a worldwide relative time scale, it subdivides geologic time based on fossil assemblages, and is divided into eons, eras, periods, and epochs
Precambrian
represents 87% of geologic time
Paleozoic Era
“Old Life” notes the appearance of complex life
Mesozoic Era
“Middle Life” dinosaurs were abundant and the era was ended by mass extinction
Cenozoic Era
“New Life” mammals and birds are abundant, the most recent ice ages occurred during the Pleistocene Epoch of the Quaternary Period
Numerical Dating
puts absolute values (e.g., millions of years) on the ages of rocks and geologic time periods: it uses radioactive decay of unstable isotopes, and has only possible since radioactivity was discovered in 1896
Nucleus
made up of protons, positively charged particles with mass, and neutrons, neutral particles with mass
Electrons
negatively charged particles that orbit the nucleus
Atomic Number
Element’s identifying number and is equal to the number of protons
Mass number
Sum of the number of protons and neutrons
Isotope
variant of the same parent atom, differs in the number of neutrons, results in a different mass number than parent atom
Radioactivity
Spontaneous changes (decay) in the structure of atomic nuclei
