chondrite—a type of stony meteorite containing chondrules, roughly spherical bodies containing pyroxene or olivine embedded in the matrix

chronostratigraphy—the branch of stratigraphy that studies the absolute age of rocks

cool early Earth—hypothesis that the surface of Earth cooled relatively quickly after the formation of the core and the Moon, such that oceans and conditions hospitable for life could exist by 4.3 Ga

Copernican—the lunar geologic period from about 1.1 Ga ago to the present

Cretaceous/Tertiary boundary—on Earth, the boundary between rocks of the Cretaceous and Tertiary periods, about 65.5 million years ago, around the time of a major extinction event

cumulates—igneous rocks formed by the accumulation of crystals from a magma

detrital zircons—zircon crystals found in erosional deposits. Some grains are as old as 4.4 Ga and are the oldest known samples of Earth

differentiated planetary body—a planetary body whose interior is formed of separate internal geologic units with distinct mineralogical characteristics, e.g., core, mantle, crust

Erastosthenian—the lunar geologic period from 1.1 Ga to 3.2 Ga ago

ESMD—NASA’s Exploration Systems Mission Directorate

EVA—extravehicular activity

Exosphere—the highest layer of an atmosphere

feldspathic—pertaining to rocks rich in feldspar minerals

Ga—one billion years

geochronology—determination of the time at which a rock crystallized, usually by radioactive decay of parent-daughter isotope pairs: U-Pb, Sm-Nd, K-Ar, or Rb-Sr

hyperthermophile—microorganisms that live in hot environments, above 60°C

igneous rocks—rocks crystallized from a magma

ISRU—in situ resource utilization

Isua greenstone rocks—a geological formation in southwestern Greenland (Isua) composed of ancient surface rocks

KREEP—lunar basalts and breccias that are rich in potassium (K), rare-earth elements (REE), and phosphorus (P)

Kuiper Belt—a region of the solar system distributed in a roughly circular disk extending from 40 to 100 astronomical units from the Sun