Anaerobic: An oxygen-free environment.
Anthropocene: The proposed name for our current geologic epoch based on human-driven climate change.
Argon-argon (Ar-Ar) dating: A chronometric dating method that measures the ratio of argon gas in volcanic rock to estimate time elapsed since the volcanic rock cooled and solidified. See also potassium-argon dating.
Atom: A small building block of matter.
Bezoars: Hard, concrete-like substances found in the intestines of fossil creatures.
Biostratigraphy: A relative dating method that uses other plant and animal remains occurring in the stratigraphic context to establish time depth.
Bya: Billion years ago.
Chronometric dating: Dating methods that give estimated numbers of years for artifacts and sites.
Continental drift: The slow movement of continents over time.
Coprolite: Fossilized poop.
Cultural dating: The relative dating method that arranges human-made artifacts in a time frame from oldest to youngest based on material, production technique, style, and other features.
Deep Time: James Hutton’s theory that the world was much older than biblical explanations allowed. This age could be determined by gradual natural processes like soil erosion.
Dendrochronology: A chronometric dating method that uses the annual growth of trees to build a timeline into the past.
Electron spin resonance dating: A chronometric dating method that measures the background radiation accumulated in material over time.
Element: Matter that cannot be broken down into smaller matter.
Eon: The largest unit of geologic time, spanning billions of years and divided into subunits called eras, periods, and epochs.
Epochs: The smallest units of geologic time, spanning thousands to millions of years.
Eras: Units of geologic time that span millions to billions of years and that are subdivided into periods and epochs.
Fission track dating: A chronometric dating method that is based on the fission of 283U.
Fluorine dating: A relative dating method that analyzes the absorption of fluorine in bones from the surrounding soils.
Foraminifera: Single-celled marine organisms with shells.
Fossilization: The process by which an organism becomes a fossil.
Fossils: Mineralized copies of organisms or activity imprints.
Geomorphology: The study of the physical characteristics of the Earth’s surface.
Glacial periods: Periods characterized by low global temperatures and the expansion of ice sheets on Earth’s surface.
Holocene: The geologic epoch from 10 kya to present. (See the discussion on “the Anthropocene” for the debate regarding the current epoch name.)
Hominin: The term used for humans and their ancestors after the split with chimpanzees and bonobos.
In matrix: When a fossil is embedded in a substance, such as igneous rock.
Isotopes: Variants of elements.
Kya: Thousand years ago.
Law of Superposition: The scientific law that states that rock and soil are deposited in layers, with the youngest layers on top and the oldest layers on the bottom.
Lithification: The process by which the pressure of sediments squeeze extra water out of decaying remains and replace the voids that appear with minerals from the surrounding soil and groundwater.
Luminescence dating: The chronometric dating method based on the buildup of background radiation in pottery, clay, and soils.
Megafauna: Large animals such as mammoths and mastodons.
Mitochondrial DNA: DNA located in the mitochondria of a cell that is only passed down from biological mother to child.
Mya: Million years ago.
Paleopathology: Study of ancient diseases and injuries identified through examining remains.
Periods: Geologic time units that span millions of years and are subdivided into epochs.
Permineralization: When minerals from water impregnate or replace organic remains, leaving a fossilized copy of the organism.
Petrified wood: A fossilized piece of wood in which the original organism is completely replaced by minerals through petrifaction.
Potassium-argon (K-Ar) dating: A chronometric dating method that measures the ratio of argon gas in volcanic rock to estimate time elapsed since the volcanic rock cooled and solidified. See also argon-argon dating.
Pseudofossils: Natural rocks or mineral formations that can be mistaken for fossils.
Radioactive decay: The process of transforming the atom by spontaneously releasing energy.
Radiocarbon dating: The chronometric dating method based on the radioactive decay of 14C in organic remains.
Relative dating: Dating methods that do not result in numbers of years but, rather, in relative timelines wherein some organisms or artifacts are older or younger than others.
Sediment cores: Core samples taken from lake beds or other water sources for analysis of their pollen.
Stable isotopes: Variants of elements that do not change over time without outside interference.
Stratigraphy: A relative dating method that is based on ordered layers or (strata) that build up over time.
Taphonomy: The study of what happens to an organism after death.
Trace fossils: Fossilized remains of activity such as footprints.
Uniformitarianism: The theoretical perspective that the geologic processes observed today are the same as the processes operating in the past.
Unstable isotopes: Variants of elements that spontaneously change into stable isotopes over time.
Uranium series dating: A radiometric dating method based on the decay chain of unstable isotopes of 238U and 235U.