Lecture 8b: Absolute Dating + Hadean-Archean Time Scales

Vocabulary flashcards covering key terms from Lecture 8b on absolute dating and early Earth time scales.

Absolute dating

Determines numerical age of rocks/minerals using radioactive decay rather than relative age alone.

Radiometric dating

Method within absolute dating that uses decay of unstable isotopes to calculate age.

Half-life

Time required for half of a radioactive parent isotope to decay into its daughter.

Zircon

A durable mineral (ZrSiO4) that incorporates uranium and is used for U–Pb dating.

Parent isotope

The unstable radioactive isotope that decays to a daughter isotope.

Daughter isotope

The product formed when a parent isotope decays.

Carbon-14

Radioactive carbon isotope used to date organic material; half-life ~5730 years.

Potassium-40

Radioactive isotope that decays to Argon-40; used to date older rocks.

Argon-40

Daughter product of Potassium-40 decay; used in K–Ar dating.

Uranium-238

Radioactive isotope that decays to Lead-206; half-life ~4.5 billion years.

Lead-206

Daughter product in the Uranium-238 decay series.

Uranium-235

Radioactive isotope that decays to Lead-207; half-life ~710 million years.

Lead-207

Daughter product in the Uranium-235 decay series.

Hadean

Earliest Earth eon (about 4.6–4.0 Ga) with differentiation and Moon formation.

Archean

Geologic eon (about 4.0–2.5 Ga) featuring crust formation and early plate tectonics.

Phanerozoic

Eon from about 541 Ma to the present, marked by abundant visible life.

Eonothem

Chronostratigraphic term for the eon-level interval of time.

Erathem

Chronostratigraphic term for the era-level interval; corresponds to a major rock-formation interval.

System

Chronostratigraphic term for the period-level interval in the timescale.

Series

Chronostratigraphic term for the epoch-level interval (a subdivision of a period).

Stage

Chronostratigraphic term for the age-level interval within a Series.

GSSP

Global Boundary Stratotype Section and Point; reference section defining a boundary.

Chronostratigraphic chart

International chart mapping time divisions (eon to stage) to rock units.

Komatiite

Ultramafic volcanic rock common in Hadean–Archean; very high melting temperature.

Greenstone belt

Archean metamorphosed volcanic-sedimentary belts linked to early crust formation.

Acasta Gneiss

Oldest rock in Canada (~4.04 Ga); provides evidence for early crust.

Shield

Ancient, stable interior of a continent consisting of Precambrian crystalline rocks.

Platform

Younger sedimentary cover over a shield, forming the continental platform.

Craton

Stable interior of a continent comprising shield plus platform.

Nebular hypothesis

Theory that the Solar System formed from a rotating solar nebula, leading to planet formation.