The Geologic Time Scale

Comprehensive vocabulary flashcards detailing the Geologic Time Scale, major historical contributors to stratigraphy, time subdivisions, and the fundamental principles of relative dating.

Geologic Time Scale

An organized and standardized system used to study the history of Earth based on specific time intervals or periods using rocks, fossils, and other geologic formations.

Nicolaus Steno (1699)

A pioneer in geology who described two basic principles: sedimentary rocks are deposited horizontally, and younger rock layers rest on top of much older rocks.

James Hutton (1875)

A scientist whose ideas centered on uniformitarianism, asserting that geologic processes operate uniformly in both frequency and magnitude across time.

Uniformitarianism

The principle stating that Earth's geologic processes are uniform in both frequency and magnitude throughout time.

William Smith (1815)

A surveyor and geologist who created a geologic map of England and demonstrated the principle of faunal succession.

Eon

The largest and broadest category of time in the Geologic Time Scale, which is further subdivided into eras.

Age (Geologic Time Scale)

The smallest commonly used hierarchical division within the Geologic Time Scale.

Phanerozoic

The current geologic eon in which we currently live.

Cenozoic

The current geologic era in which we currently live, beginning after the mass extinction of the dinosaurs.

Mesozoic

The geologic era widely recognized as the "Age of Dinosaurs," concluding with a massive dinosaur extinction event.

Epoch

A subdivision of a geologic period defined by notable events and specific planetary characteristics, such as the Paleocene.

Quaternary Period

The youngest period of the Cenozoic Era, spanning the last 2.6 million years, characterized by ice ages that influenced plant and animal distribution alongside human civilization.

Neogene Period

A Cenozoic Era period lasting 23 million years, subdivided into the Miocene and Pliocene epochs, marked by significant climate shifts, organismal evolution, and ecosystem changes.

Paleogene Period

A Cenozoic Era division following the Late Cretaceous that spanned from 66 to 24 million years ago, divided into three epochs.

Cretaceous Period

A division of the Mesozoic Era split into Early and Late Cretaceous, characterized by the breakup of the supercontinent Pangaea and the evolution of the first flowering plants.

Jurassic Period

A Mesozoic period occurring between 201 and 145 million years ago, divided into Early and Late Jurassic, highlighted by the dominance of dinosaurs and the appearance of the first birds.

Triassic Period

A Mesozoic division occurring between 252 and 202 million years ago, split into Early and Late Triassic, marked by the earliest evolution of dinosaurs and mammals.

Permian Period

A Paleozoic Era division lasting between 292 and 253 million years ago, noted for the tectonic assembly of Pangaea and a major decline in marine animal life.

Pennsylvanian Period

A subperiod of the Carboniferous lasting between 323 and 299 million years ago, defined by dense vegetation, warm and moist global conditions, and high oxygen levels.

Mississippian Period

A subperiod of the Carboniferous lasting between 359 and 324 million years ago, noted for the emergence of the first land-dwelling vertebrates, such as early tetrapods.

Devonian Period

A Paleozoic division lasting between 419 and 360 million years ago, famously referred to as the "Age of Fisheries."

Silurian Period

A Paleozoic Era division lasting from 443 to 420 million years ago, notable for the evolution of the first vascular plants and the subsequent colonization of land.

Ordovician Period

A Paleozoic Era division lasting between 485 and 444 million years ago, characterized by primitive fishes, hard-shelled organisms, and the widespread development of shallow tropical seas.

Cambrian Period

The earliest Paleozoic period (541 to 486 million years ago), during which the first continents formed alongside an evolutionary explosion of diverse life.

Cambrian Explosion

A geologically rapid diversification and evolutionary radiation of multicellular organisms during the Cambrian Period.

Fossils

Preserved remains or traces of once-living or extinct organisms found across various rock strata, providing crucial records of Earth's biological history.

Relative Dating

The methodological process of establishing whether a rock unit or geologic event is younger or older compared to others without calculating numerical absolute ages.

Stratigraphy

The scientific branch that studies the succession, distribution, and layering of sedimentary rocks.

Superposition

The stratigraphic principle stating that within undisturbed sequences of sedimentary rocks, older layers lie at the bottom and younger layers form on top.

Original Horizontality

The principle stating that layers of sediment are initially deposited in an essentially horizontal arrangement under the influence of gravity.

Lateral Continuity

The principle stating that sedimentary layers initially extend outwards laterally in all directions across a depositional basin.

Cross-cutting Relationship

The geologic principle indicating that an igneous intrusion or fault cutting through existing rocks is inherently younger than the rocks it cuts across.

Principle of Inclusion

The relative dating concept stating that rock fragments or inclusions contained inside a rock body must be older than the host rock that envelops them.

Principle of Fossil Succession

The principle stating that fossil assemblages follow one another through time in a definite, identifiable order, meaning strata containing specific fossils reflect the time period in which they lived.