Geologic Timescale Lecture Flashcards

Vocabulary terms and definitions from Lecture 9 covering absolute dating, relative dating, and the geologic timescale.

Absolute Dating

Techniques that provide the number of years since an object, such as a rock or fossil, formed.

Relative Dating

Representing time as an ordinal sequence of events placed in order without providing an actual date in years.

Radiometric Dating

A technique that uses known decay rates of unstable radioactive isotopes trapped in objects to determine their absolute age.

Isotope

Varieties of an element that differ in the number of neutrons in the nucleus and thus have different atomic weights.

Alpha Decay

The emission of an alpha particle consisting of two protons and two neutrons from an unstable nucleus.

Beta Decay

A process where a neutron changes into a proton and an electron, with the electron emitted as a beta particle.

Gamma Decay

The emission of electromagnetic radiation (gamma ray) during alpha or beta decay.

Decay Chain

A series of radioactive decays that occur when the daughter product of a previous decay is also unstable.

Half-life ($t_{1/2}$)

The constant amount of time required for $50\%$ of the unstable atoms in a sample to decay.

Zircon ($ZrSiO_4$)

A mineral common in granites that incorporates Uranium atoms ($U^{235}$ and $U^{238}$) during crystallization, used for radiometric dating.

Closed System

A necessary condition for radiometric dating where there is no escape or addition of parent or daughter atoms from the outside.

Lithostratigraphy

A relative dating method based on the stratigraphic succession of rock units.

Biostratigraphy

A relative dating method based on the stratigraphic succession of fossil taxa.

Magnetostratigraphy

A relative dating method based on the stratigraphic succession of Earth's magnetic reversals.

Geodynamo

The generation of Earth's magnetic field by electric currents flowing in the rotating, liquid outer core.

Remnant Magnetization

The orientation of the magnetic dipole "frozen in" to lava as it solidifies into rock.

Detrital Zircons

Zircon crystals that weather out of igneous rocks and are incorporated into sedimentary rocks, used to determine maximum depositional age.

Ages/Stages

The shortest nested interval used to subdivide geologic time.

Eras/Erathems

The very long nested intervals of geologic time that contain periods, epochs, and ages.

Carbon-14 ($C^{14}$)

A radioactive isotope with a half-life of $5,730$ years, applicable to dating geologically young biological material.